Atomic Energy Control Board

,';.i ... .' .•.•...-. -.;: • . \ • •

Atomic EnergyControl Board p||f^

INVESTIGATION OF THE EXPLOSIONHAZARDS OF HYDROGEN SULPHIDE

(PHASE II) - APPENDICES

by

I.O. MoenDefence Research Establishment Suffield

I* Atomic Energy Commission de contrôleControl Board de l'énergie atomique

PO Box 1046 CP 1046Ottawa Canada Ottawa, CanadaK1P5S9 K1P5S9

Canada

INF0-0180-2A

INVESTIGATION OF THE EXPLOSIONHAZARDS OF HYDROGEN SULPHIDE

(PHASE II) - APPENDICES

by

1.0. MoenDefence Research Establishment Suffield

A research report prepared for theAtomic Energy Control Board

Ottawa, Canada

January 1986

Research report

APPENDIX A

FLAME ACCELERATION TESTS

PART I: Spherical and Hemispherical Configurations

TABLE AI - Fuel-Air Flame Acceleration Tests: Spherical and Hemispherical

Item References Configuration Fuel Flame OverpressureVelocity MaximumMaximum (bar)

(m/s)

Remarks

A l . l Dorge et a l . (1976)Wagner (1982)

Al.2 Deshaies and Leyer (1981)

Charuel and Leyer (1983)

A1.3 Lind and Whitson (1977)

Cubic containers,paper walls removedprior to ignit ion onbottom steel plate/hemispherical gridobstacles (see Fig. A l . l )(0.6 x 0.6 x 0.6 m3 max)

Hemisphericalsoap bubbles;D = 4 - 40 cmNo obstacles

C 2 H 22 <

C H 8

C,H,

1503016

534

D = 20 cm(no obstacles)

Hemispherical Balloons;5 and 10 m radiusNo obstacles(see Fig. A1.3)

C,HP3 8

CH,C 3 H 8

J oC2H-°C 2 H 2r u

20

8.912.6

22.535.417.3

3 grids1 grid1 grid

0.0024 Jet igni t ion

Plastic balloonsintact prior totests

5.5

TABLE AI Continued... il

Item References Configuration

Spherical balloons; 12 m3

{no obstacles)Homogenous mixtureStrat i f ied mixture6.3 x 6.3 x 3.15 m3cloud. No obstacles

Fuel

C2H4

C HCXc X

FlameVeloci tyMaximum

(m/s)

24

38182920

OverpressureMaximum

(bar)

0.0125

—0.0080.015

=0.001

Remarks

Balloon in tac tprior to testsBallon destroyedprior to testsEnclosuredestroyed priorto tests

A1.4 Brossard et al. (1983)Brossard et al. (1985)

Al.5 Schneider and Pfortner(1981)

Hemispherical balloons.Radii 1.53, 2.88, 5 and10 m (see Fig Al.5)No obstacles

84 0.06

Figure Al.1Dôrge et al. (1976) and Wagner (1982)

Mesh Grids60 cm x 60 cm x 60 cmC2H4, C2H2 and C3H8

Flame inside and outside gr id

Paper «rails

Oxygen

Hydrocarbon [ Nirroo»n

Gos inlet

outletMeiol-ptaiE

Fig. 1. Expérimental arrangement.

Table 1. Specification of wire screens

diameterof the grids cm

9, 14, IB

9, 14, IB

9, 18

9, 18

9

9

9

9

9

S

9

9

9 , 1«. 18. IS

mesh size 1 SOB

1 .6

2 . 8

3

6 . 3

6 . 3

3

1

£.3

10

16

S

3

1.S

v i r e dl&meter d m

0 . 8

o.e

O . 5

2

O. 8

1.5

O.2

1 .4

1 .8

1 . 8

1 .8

1 .5

O.2S

Figure Al.l Continued.

a = Velocity (outside gr1d)Velocity (inside grid)

Rew = Reynolds numberbased on laminar flamespeed and wire diameter

I5 mmto-I)

TOO BOO 900K» 2O0 SOO «OO MO «00

Fig. 2. Acceleration factor a as a function of Re for hydrocarbon-air mixtureso - / (Re . ) : • . CH^air; x. C,H«-air.

ia-\)

6.3 mm

10 mm

1000 2000 1000Re.

Fig. 3. Acceleration factor a as a function of Re. for C3Hj-air. C,H<-atr and CiH<-oxygenenriched air mixtures, a - f(.Re;O. C,H,-»ir: • . CjH^-air or dH^-oxygcn enriched air.

Figure Al .2Deshaies and Leyer (1981)Charuel and Leyer (1983)

Hemispherical soap bubbles; rad i i 2-20 cmNo obstaclesC2H4, CH4 and C3H8

.to CRO

P.P

Sparking tiec>roOes

external charge

« 200

Figure Al.3Lind and Whitson (1977)

Hemispherical balloons of rad i i 5 and 10 mNo obstacles

Sua ary of Results of Hemisphere Tests

Test

No.

57131123641110B14151817

Size,meters

55105105551010105•555

Fuel

Methane"

Propane

Ethylene Oxide"

EthyleneAcetylene

"Butadiene

Concentration,Volume X

10.010.010.04.04.05.05.05.05.07.77.76.53.57.73.5

HorizontalVelocity,

ml»

5.8... *5.2.. .b

6.1.. .*6.98.39.613.4

14.78.83.6

23.73.9

VerticalVelocity

at 3 a.

7.37.36.56.37.87.49.510.29.9

15.216.017.34.6

35.4

5.5

at 8 m.

•/•

8.9

10.6...

12.622.522.4

* Burning fuel in the instrumentation channel distorted the shape of the flame and nohorizontal velocity could be obtained.

Test performed in daylight and flame base vas insufficiently visible Cor horizontalvelocity to be obtained.

Fi gure Al.4Brossard et a l . (1983, 1985)

Spherical balloons; homogeneous and st rat i f ied mixtures of C,H -air andC2H2-air 2 *No obstacles

COMPARAISON . EXPERIENCE/ MODEUSATION D'UNE DEFLAGRATION A VITESSE CONSTANTE .

- Figure 4 _

Calculs / • E 07 o ]

V-Cte Is E10 o { Expérience

" e t rf max ' » E W » 1

fissurés

essais air • éthylène , volume * 1Z m3

m/s

E 10= T76 m/s

= 0.33

TO r ( m )

Table 2 Influence of the ch«rjt envelope

on the piessuie field

Equivalence

C j H 4 -

C 2 H 2 -

ntio of the

lir11 3

18

Miiliue

Tible 1 :

^ F

Observed Speeds

lm/>)

8.5II

2017

Vp man {mis)

II17

3238

TetlRRo

CHARLES 13(entelope destroyed bythr cxploaon lUelf)

CHARLES 14(envelope destroyed 150 nutfler i(nition)

CHARUS 1-5(envelope destroyed 100 nubefore ignition ofthe chirge!

16

6 7 ?

-

-

2 3

9 4

14

4.2

UP

74

6

9

33

4.4

4 5

6 8

2 A

mbir)

6 6

3.8

6

2 1

2 3

8 8

IS

4.5

2 2

S i

9

29

vF(-M

TK11

-

-

84

calc

87

8 2

7

<m/

me»

-

26

16

Tulc

199

23 2

15 T

Figure Al.5Schneider and Pfortner (1981)

7.5 - 2100 m3 hydrogen

•L

10 -

10 r

5 -CHT 20-26

I \ I I1 2 5 10'

Measured pressure-distance relation

of the free gas cloud testa

Figure Al.5 Continued...

TestNr. CHT

1

2

3ft

8

5

6

7

rg

(m)

1-53

1.53

1.53

1.53

1.53

2.88

2.8B

2.88

C

(voi<)

28

-

28

27

27

30

28

i l

"o<kg/m3)

0.873

0.873

0.873

0.881

0.881

0.851

0.87 30.(181

"F( k g / a ' )

0.113

0. 113

0.1130.116

0. 116

0. 108

0.113

0.116

• l(m/s)

-

2.31

2.3«

2.21

2.56

2.31

2 .?1

• 'C m / 3 )

50.0

i » 9 . i

" 7 . 9

U5.U

1 5 . 8

6 1 . 0

52.9

63.3

* max(m/a)

.

50

51

19

-

58

55

56

f T T T

_

2.77

2.83 2 - B1) 10.07

2.92

2.85

3-OS 3.08±0.09

3 - 3 "

r - radius of the balloon

c - H y concentrât ion of the mixture

P /pr - der-sity of the unburnt/burnt gas° mixture

laminar flame front velocity

s' - calculated flame front velocity

s1., - maximum measured flame frontaax velocity

Table 6: Free gas cloud tests (first series)

Te«t-Nr

CHT

20

21

22

23

24

25

26

27

39

4 0 *

11

13

34*

*) . I t

(ml

1.53

1.53

1.53

1.53

1.53

1.53

1.53

2.88

2.88

2.BB

5.0

5.0

10.0

Net I

E

(Joule)

1000

1000

1000

10

10

10

1000

314

314

150

c(Vol.I)

30.1

28.6

29.2

29.1

29.1

29.5

29.2

27.2

29.4

29.5

31.0

25.9

29.7

PL(Torr)

749

730

737

736

732

736

743

734

739

739

755

757

742

C O

10

6

9

9

9

8

8

13

6

6

6

10

10

po

0.8849

0.8918

0.8840

0.8839

0.8791

0.8825

0.B943

0.8902

0.8936

0.6925

0.9889

0.9609

u.eeoe

(I

0

0

0

0

0

0

0

0

0

0

0

0

0

°F'«/<"• )

.1075

.1114

.1098

.lioo

.1100

.1090

.1098

.1157

.1093

.1090

J 0 7

.1203

.1084

( * / • )

2.44

2.22

2 . 3 2 •

2.31

2.31

2.35

2.48

2.14

2.31

2.32

2.50

1.94

2.39

(m/.)

49.7

45.8

45.2

42.4

45.5

46.2

46.2

46.1

49.0

57.0

62.0

49 .5

72 9

n i x

-

46

46

42

41

45

39

43

50.5

54

59

48

83.6

'T

2.47

2.59

2.46

2.26

2.22

2.37

2.07

2.59

2.67

2.85

2.83

3.09

4.30

2.33

2.63

2.96

4.30

Table 7: Free gas cloud tests (balloon tests)

(second series)

Part I I : Cylindrical Configurations

TABLE AH - Flame Acceleration Tests: Cylindrical

Item Reference Configuration Fuel Flame OverpressureVelocity MaximumMaximum (bar)(m/s)

Remarks

A2.1 Moen et al. (1980)Moen et al. (1981)

A2.2 Beale (1980)Moen (1982)

A2.3 van Wingerdenand Zeeuwen (1983)

A2.4 Zeeuwen andvan Wingerden (1983)

Central ignition betweentwo plates (0.6, 1.2 and2.5 m diameter),spiral tube obstacles(see Fig. A2.1)

Central ignition betweentwo plates (0.6 m diameter)Forest of cylindricalobstacles (see Fig A2.2)

0.6 x 0.6 m2 in a 1 m3

vessel. Forest ofobstacles, (see Fig. A2.3)

1000 Kg propane.Forest of vertical pipeobstacles (0.3 and 0.6 mdiameter, 1 and 2 m high)(see Fig. A2.4)

CH,

H2S

CH,,

CH.

CH,CHCXC H2

3H8

400

50

70

60

727204052405

66

10

0.64

0.02

2.5m diameter

1.2m diameter

1.2m diameter

No top confinementTop confinementNo top confinementTop confinementNo top confinementTop confinementNo top confinement

Covered obstaclearrays (25 x 25 m2)Uncovered

...II

TABLE All Continued.

Item Reference Configuration Fuel FlameVelocityMaximum(m/s)

1030

24420

225160

=4

OverpressureMaximum(bar)

—

0.020.7

1.80.8

—

Remarks

No top confinementTop confinement

No top confinementEdge ignition withtop confinement

Top confinementTop confinement

Pancake shapedcloud on solidsurface

A2.5 van Wingerden (1984)van Wingerden andZeeuwen (1985)

A2.6 Hjertager (1984)

A2.7 Leyer (1982)

0.5 x 0.5 m2 in a 1 m3

vessel pipe rack obstaclearray.

4 m x 4 m x max 1.6 mPipe rack obstacle array(see Fig. 2.5 )

Radial disc(0.5 m radius)Pipes and flat typeobstacles (see Fig. A2.6)

Soap bubblesRadius = 9, 22, 35.5 cmHeight = 2 . 4 - 9 cmNo obstacles (seeFig. A2.7)

Figure A2.1Moen et al. {1980, 1981)

Central ignition between two platesShchelkin spiral obstaclesCH4 and H2S in air

îgn i tion Wi res

Gas Inlet

Spacer

Streak Camera

Schematic diagram of experimental selup for flame propagallon experimenis.

IGNITION WIRES

.\> / / / / / / / / / 1 1/ / / .- t:, I i\ \ 1 : • 1 ! I 1' ,'f\

Ui O! O Otri 11 / / / / 1 h / / / / /11 i /////////// 1 TT 1 /I m

GAS OUTLETGAS INLET

GAS OUTLET

schemtllc cross-stcllonil vltw of experimental chamber showing the obstacle con-figuration.

Figure A2.1 Continued.

ti

D = 2.54 cm,H = 1.27 cm, P = 3 cm,Rp = 70 m/sec

D = 2.54 cm,H = 1.27 cm, P = 3 cm,(H2S). RF = 50.4 m/sec

Figure A2.1 Continued...

R.m/t 6, m/t

r cm.FliTif ttlocli) Rf * i distance of propagation r for ilotchiotnrirV meihanr-alr Flimn

dolid runci carfe»p<md to Eq. (6) -llh o-O.Jt and p,~J7.$ tm, da»*td cvr»ei trc dra»nihri>UKh data puinl» (or x<60 cm): a) Plaiik lubt (pirali, i / - 4 ttn,/>- JOcm on boih top andKotiom plaiei, ////}-O.«7; b) plmiic lubt iptraf on bollom plair, M/J5-0.S7; c) plasiic tubetpirab. o l'ip plaît nnl) ,0 tup and bntlnm plaît, ti/t)-f).4; d> «lailk l«be »»lr«l on bottom

r cm.Flame *tlodt)' rf^ *• distance of proptpilom r tor ttoiehiomtuic mtlhan«.alr fiam^

(bolid c«r»« coftnpond to Eq. (7) «Hih « - 0 J 1 and p# »37J cm): a) copper lube spiral. «-1.2Scm. p •• 3-t cm «n toiiem ptalc, p(at(ic Itivc apiral; / / • 4<m, p» 10 m • • lap plate: W//>- 0.5Ï;h| c«pp«r tabc iplra] on bottom plate, HfD^Q.H, c) copper lube iplnl on bottom plat?.mD" 0.25: d) copper i»be tpfral en bottant plate. HtD »II.I3 fik» experimental point ai 30 cm ufrom the laboratory rnulUof Mocatd aJ. (1*M)].

Figure A2.2Beale (1980) and Moen (1982)

Central ignition between two plates 0.6 m diameterCylinders (125,2.5 cm diameter) as obstaclesCH4

Top p l a t e

Steel bandCeramic cap

\xi 111 n y / 1 1 i 1 1 /7t

I g n f t o r

O b s t a c l e

/ / / / / / / / is v / n i

111 n M 1111111 i/i i\\i 1111111 r m 111 n

C a s o u t l e t

B o t t o m p l a t e

Gas i n l e t

oo o

o oo

o • o

o ,

10 c

o 'o --o

o o "Oe.o

O O o'

Q o

10 cr

o -o o o

o ° ° ° o o o© °~°- © o o o

* o ° o ° o o oO o Q O O O O O

o o(~) " (" igni t ion Q (

BL O I U 1 1 'or.il °

° o o o o © © ' oO O O O e o ° C

o o o ° o o °

o o o o

oo o o

oo o o

o oo ° o

radial sful l fo , , , ,

o o o

~t" igni t ion

O full fore . r

_̂ r c d i a l &

i u I i l o r c t


Cyl'nriar Fane» f l»n«rI R - 0 SI H / o - 1

£

2 »

« o •

to

. 30'

OtSPLACCMCVT I c m ]

Acceleration and decay of a stoichiometric methane-airflame upon encountering obstacles . a) Planar flamein channel with a fence of cylinders of height H = 2.5 cmand diameter D = 2.5 cm providing a blockage ratio B.R. =0.S1 to the flow. The fence was placed at a distance ofSO am from the ignition source located at the closed endof the channel, b) Cylindrically expanding flame withfence of cylinders (H=D=2.5cm) placed 17 cm from thecentral ignition source, c) Planar flame in a channelwith a screen of blockage ratio B.E. = 0.60 placed 30 cmfrom the ignition end. d) Cylindrically expanding flamewith a screen of blockage ratio B.R. = 0.60 placed 7 cmfrom the central ignition source.

Figure A2.3van Wingerden and Zeeuwen (1983)

0.6 x 0.6 m2 in a i m 3 spherical vesselForest of obstaclesCH4, C2H4, C2H2 and C3H8

obstacle configuration

850779

miifliiir

1-m3 explosion vessel

Experimental set-up during small-scale experiments.

60cm

00000000-00000000-00000000000000000000000000000000OOOOOOOO00000000

top - v ie

6IWU-2

n n n n n n !

60 cm

side - view

Schematic diagram of repeated obstacles during sraall-

and large-scale tests. Not to scale. D = stick diameter,

H = stick height, P = pitch.

Figure A2.4Zeeuwen and Van Wingerden (1983)

1000 Kg propane into array of vertical obstacles, with and without topconfinementC3H8 .

1 - 1 tllllil

View of obstacle array consisting of 7 rowsof 10 sewer pipes (pitch 3 m).

IS -

20 -

15 -

10

5

obstacleorroy

• uncovered orroy -• covered orea 7*7 m̂i covered Oreo 13«13m'• completely covered orroy

0.' «J» 1.2 2.0time Is)

Flame paths measured for variousdegrees of vertical confinement

10.0

1.0

0.1

• A

D

obstacle

array j

a

w

\N

tes» no.2l 'test no.2Slest no.27test no.28

-

\

0.1 1 10R«R/lt/po)V3

Peak pressures measured in testswith top confinement

Figure A2.5van Wingerden (1984)

Van Wingerden and Zeeuwen (1985)

Pipe racks0.6 x 0.6 m^ in 1 m^ vesselC2H4

Uncovered20 mm diameter pipes (as above)C2H4

Part top confined

101.6 nm diameter pipes4 m x 4 m x l . 6 m maxC2H4

Uncovered and part top confined

Figure A2.5 (continued)

View of the small-scale obstacle array mounted in thecentre of the 1-m3 explosion vessel

View of the horizontal tubes used in the large-scale tests


h «O.I DP-7.2S0

i loryr i

i tMolt not*

100

50

0C

t

\

UA. .' V \ / ^> -̂̂ *̂— '

1 I 3

1

i 03

0.11OU

- ^ ^

Figure A2.6Hjertager (1984)

Radial dise, 0.5 m radius with obstaclesC3H8, CH4Top confined

IGNITION

PRESSURETRANSDUCE

ION PROBES

OBSTACLES

Schematic diagram of experimental set-up.

2 Û

16

12

1O

OB

06

0 *

oa

0 1

OOB

OOS

0 0 4

0 0 2

Typr * «toi

p/n

itdf o - » « * U" F t o l

: i^mn 16oww C«*^ j » ^ ^6 ? 6 2* f V ^

/

/

/ clV-"«

/ /y*

/O//1 / "

/A/// / /

03 0* 01> Of, 07 06

Maximum prtuure in ridial di«c «xpcrimenU venus block ice ritio for variouiobsUelc (hapes. -

Figure A2.7Leyer (1982)

Pancake shaped soap bubblesRadii 9, 22, 35.5 cmHeight 2.4 - 9 cmNo obstaclesC2H4

Sketch of the cylindrical charge experimental ar-rangement.

Part I I I : Channel Configurations/Partial Confinement

TABLE AIII - Fuel Air Flame Acceleration: Channels/Partial Confinement

Item Reference Configuration Fuel Flame OverpressureVelocity Maximum(m/s) (bar)

Remarks

i ) Weak I g n i t i o n :

A3.1

A3.2

A3.3

A3.4

Chan et a l . (1983)

Urtiew et a l . (1983)

Sherman et a l . (1985)Berman (1985)

Pfôrtner et a l . (1983)Orth (1983)

Channel 1.22 m long by127 x 203 m2.Repeated b a f f l e obstacles32, 50 and 76 mm high(see F ig . A3.1)

Channel 0.9 m long0.3 m high x 0.15 m high.Repeated b a f f l e obstacles35, 92 mm high(see Fig A3.2)

Channel 30.5 m long ,2.44 m h igh , 1.83 m wide.No Obstacles(see F ig . A3.3)

Lane 10 m long,3 m x 3 m cross-sect ionMo Obstacles(see Fig A3.4)

CH.CH,,CH,C\

C3H8

H,(18.4S)H?(25, 30%)H,(12-28%)H,(15-18%)H2(24.8%)

H2(36%)

160-350 0.1530-9010-15

5

20

150 0.26Trans i t ion to detonation127 0.17115 0.1Trans i t ion to detonation

Trans i t ion to detonation

Closed top8% open top23% open top50% open top

Open top(obstacles o f f groun

Closed topClosed top50% open top13% open top13% open top

Open topwi th fan

I

.../M

TABLE A l l I - Continued...



Remarks

ii) Jet Ignition:

A3.5 Schildknecht & Geiger (1982) 0.5 m x 0.5 m driver(Schildknecht et al. (1984)

Stock and Geiger (1984)

A3.6 Schildknecht (1984)

A3.7 Stock and Geiger (1985)

A3.8 Moen et a l . (1985)

with/without turbulencegenerators into4 m x l m x l m sectionwith various degreesof confinement(see Fig. A3.5)

Into lane4 m x l m x l m lane(see Fig. A3.6)

Into lane1 2 m x 3 m x 3 m(see Fig. A3.7)

Into 4 m long plastic bag2.0 m in diameter(see Fig. A3.8)

=850 (Jet) 1.3

=850 (Jet) 3.8

Plastic only onthree sides and end

Partial confinement

Transition to detonation Lane with plastic top

Transition to detonation Lane with plastic top

600 (Jet) Transition to detonation

Figure A3.1Chan e t a l . (1983)

Channel 1.22 m long by 127 x 203 mm2 cross-sectionRepeated baf f le obstaclesCH4

~tl_i i ' i i

Gas inlet

~r

• Perforated top plate

rObstacles along central axis

I I I I I I I

Schematics of experimental apparatus.

0.4

0 3

I °2cea.CEUi

MEASURED PRESSURE

PREDICTEO PRESSURE

0.1

0 010 3 0 4 0 50 6 0

TIME , m»The pressure development in a fully confined channel.

1 6 0

140

I 120

zo

100

«IIJl' 11 ,.' 11 1

1

1 1I 1

I

1 1

E

aUJIUa.tn

UJS

8 0

6 0

4 0

7020

O h * 76 mm P= 101 mmû h=76mm PM52 mm* h =51 mm P = I52 mm• h - 51 mm P*IOI mm

ëf-

20 40 60 eo 100

OEGREE OF CONFINEMENT , %Flame speed at 1 m from ignition for various de-

trees of confinement and obstacle configurations.

Figure A3.3Sherman et a l . (1985)

Berman (1985)

30.5 m x 1.8 m x 2 . 4 m channelConf ined - 50% top open

H2

FLAME facility

Illustration of the FLAME facility(FLame Acceleration Measurements andExperiments).


Experiment Conditions and Results for FLAME Test Series 1.

TestNuaierF-

12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

IB19

TopVentingArea,*

50

50

50

50

50

50

0

0

0

0

0

0

0

0

13

13

13

13

13

HydrogenHole

Fraction,*

12.4

19.7

20.8

28.0

12.6

15.5

12.0

18.4

6.9

12.3

12.9

24.7

12.0

30.0

15.4

17.6

14.9

18.1

24.B

PeakOverpressure,

kPa

2.B

17.2

3.1

1.2

26.1

1.2

3.1

95.6 & 1149

248 & 2100

3.1

10.3

EquivalentPlanar

Flame Speedm/s

7*

49*

57*

106-127

4-12

17-19

8-17

70-175

1.17*

7-12

13-34

160-374

190-1070

22-50

60-115

87-132

Coranents

limited burn

detonation

data lost

detonation

detonation

horizontal propagation velocity

Figure A3.4Pfbrtner et a l . (1983)

Orth (1983)

Lane 10 m long, 3 m x 3 m cross-sectionNo obstacles, but with fanH2

23 29 30 31 32 33 34 35 36 37 38

Ce fonction

deflagration

Top: Flame front velocity and typical pressuretime curves at 3. "# 6 and 8 m distancefrom the ignition point

Bottom: Flame speading; dashed lines: deflagration,full lines: detonation


Test Nr.

CHT 35

CHT 36

CHT 37

CHT 38

CHT m

GHT 12

GHT 13

CHT ill

CHT 15

CHT 16»

CHT <I7'

CH2Vol %

37

39

39

no

38

36

n 1

3B

ii 1

m37

DegreeofConfinement

0.65

0.72

0.72

0.72

0.72

0.72

0.72

0.72

0.72

0.72

0.72

225

225

225

113

171

171

203

203

Fan• P-

-

-

-

(1

(1.

C1.

(0.

(0.

(0.

(0.

(0.

.0)

.0)

.0)

.5)

75)

75)

9)

9)

Temp.°C

13

5

12

18

20

19

15

16

max(m/a)

161

200

196

(600)

2220

2?50

250

230

280

APnax(mbar)

120

165

200

600

1.000

20,000

300

-

1150

H80

120

Remarks

broken walla

reinforced walla

failure of ûp-measurements

*) preliminary evaluation

Lane trials (10 x 3 x 3 • ' ) , H^'-air mixture

Figure A3.5Schildknecht and Geiger (1982)

Schildknecht et al. (1984)

0.5 m x 0.5 m by 1 m long driver into 4 m x 1 m x 1 m sectionVarious degrees of confinementC2H4

Hg)x:esc^indqkeilskomero Typ HYÇAM

HYCAM Iwchlv.-eise Beoboch!von der Seite !

<=• Druckcufnehmer

O Gemischprobenenlnahme

't Zùndkerzen

Turbuienzqei'erctcr


solid wall

plastic fo i l wall

i 6

d>, \S/ /A _,

'V/JA~

r /v / / / /1

| / / ' ' ' •

y s / /s, s s /

"U

IV

VI

VII

VIII

Jet Ignition Configurations


/////////////

/

1. /% /

V,m /

/

km iPl P2 P3 1 % P6 P 7 P 8 ,

_ ] , *<•

50

c.brc: Gûsprobeneni nohme }'Seilenansicht

F o t o - B l i t z

HYCAM

J:-\V^

i

I

i

I

I

"î Pn

Konfigurationen

I-VI

- p i10 -

•tfï P2 P3 P

s s s// IBunkerwand ]

3 P P p , «-

.5. -6. ;'. }r? L

• 2 «3 j*

•v.

; zz i

Konfiguration

VII

An.75 1.25 0.75 025 0.25 0.75 1.25 1.7s[ m

1m

*—1m —

! A Ai

Lope der Oruckan fnchmrr un cl Son rt critter HochgCBChw

Konfiguration

VIII

M 1:50

r Dlickfcld

Figure A3.5 Continued..,

Zuaammenstellung der in den einzelnen Anordnungen aufgetrctenenn.oximalen Werte fiir Oberdruck und apezi fiachen Impuls

K o n f i g u r J t ] o n

r. «* m i 3 c h -

ni 11 i 5

-

0,0025

-

ohnc

0. 1

I

0 ,07

2 . 2

ischxolkc

0 ,3

I

i . a i

olmc

0, 1

V I I

. . .

m i t

0 , 3

IV

3 ,6

7 ,7

F r n s i r . , 1 , 1

olmr n, j I

0 ,1 b , 3

VIJI VIII

2.35 1

2 , 1

fm 1

free cloud

P

0,7=

0.25

distance, m

Peak overpressure in the free cloud vs. distance fromthe opening of a room where jet ignition originates,for various orifice ratios (F area of the opening,F cross «ection of the room)G


1.0

0,5

jet igni tionwi tb obstacles inside

jet ignition withoutobstacles inside

30 A0 50

i g n i t i o n by a spark outside the room

m = 0,006 bor

100

-0,01-

Pressure signals at the point of maximumoverpressure in the external cloud for jetignition and spark ignition

Figure A3.6Schildknecht (1984)

Jet ignition into 4 m long, 1 m x 1 mCross-section laneH2

O Cf(opening) ., :

(confinement)

Experimental arrangement and measurement systems(Versuchsjinlagc und Hesstcchnik) for ll-scrics oftest^ on strong jet ignition

(pipe connectors)

Rohrverbindungsklemmstucke

j

•

\\Rohr $50 mm

T

Framework of pipes for holding the gas mixturein the channel (Konstruktion zum Halten desGentisches In der Casse)


Important Hewultw af Second T*3t Mtrlrt

(2ui*uenBtcilwi9 der vlcbclçcten Verauchverfcbnls»* dec- «wvlten

Venuchi-Nr.

(ErperlaennusberJ

Offnungi-verMJtnlf(Orifice

Seltenlljigeder Oltnuntj(Length of

orifice]

c»

kritltcher Turbulent-DurchaesBer generator(CrltU.l tubedlaaeter]

(neln

(yell (nol3»

irelb»r

K,-Konientf* 11onen(H? Concentration)

Vol.» H2

(lnaldej (outilde) (Inilce) (outsldel

H 05

H OS

H 0?

H 08

H 09

H 10

H 11

o.s

0.5

0.5

0.1

0.1

0.1

0.1

35.3

35.3

35.3

15.8

15.8

15.8

15.8

16

18

le

le

18

le

le

15

3

15

1.3

1 . 1

6

0.65

15

15

2.8

1

3 * '

31

46.9

26.6

Detonation innerh*lb der Trclbcritufe (detonation J/iiide the dr ctlon.)

Detorutlon innen und «upen (detoo*tion Inoide *nd oututde.)

Cber-jifKf tue De ton* t ion in AuP«nr*u» (tr&niltlon to deton&tton In outside region.)

•comité er*t «inJçe T*çe aplter *n«ly<iert uerden, io d»P «•hnchelnllch H- «ut der CASMUS diffundiert l i t ,ci dorft* wihrend <Sei Vertucha ctecKlosctrlichea Ccniich vorçclcgcn hoien

(could onlj be aniljied « few d«yi l*tcrr io th*t the M. prob»Lbly diffused out of the çaaa man auplejduring th« «zperlarnt, the alsture «*• probably •totcfUotietric. )

beatlutt 4ui Laufxelt del Druckaigmla (detcralned bj the run tlae of th« preaaura •lgnali. f

. Mitte (Pfod linBtld19)

o rechte Wand [Pfod HinBiId19)

o linke Wond |PfodJIJinBild19J

Oeh-Welle {Pfad IV inBiid 20)

• Oruckfront cm Oruckoufnehner

o Det- Front om Druthoufnehmer

v = Ulm/sI Fttillroh\oihnl

•Distance-time diagram (trajectory) for the flame front or,respectively, the detonation front, and for the pressurefront for test H 11 (Weg-Zeit-Diagramm der Flammenfront bxv.Detonationsfront und der Druckfront)

Jet ignition into lane1 2 m x 3 m x 3 mH2

Figure A3.7Pfortner (1984)

Stock and Geiger (1985)

ICT • baarlaantafry H. flOrtnar

I Concept and axparlMnt taaifn »r lattal la frankfurt)

DrpariMnt• e .

OrlfleaRatio

Concantratlon

lni vout»

• t a a l Plpaa DOT

aa Ko Taa Mo

Nu. Pratsura Ban

Lki

IÂ2

0.1

0.1

21. ) 21.»

21 20.1

21

21.1 X1»

l . S - •

tfttonatlon

1AJ

1A4

0.1

0.3

-20.2

22.4

1.1

o.s

l t . t

dttorn ilorprffisurt

IA5 0 .3 1».» I t . » 20 0.36

Ara* of tha vantTotal araa of tlta front plata of tba eonflna*ant

EOT eccurratf at tha alpa on tba fround (eornar) half lay down tha cbannal.

COT occurred on tha fround akotit ana channal dlaaatar donnât raaa.

Figure A3.8Moen et a l . (1985)

Jet i g n i t i o n in to 4.0 m x 2.0 m diameter p las t ic bag5% C2H2

WINDOW\\

CAMERASHELTER

for

win u i ii

\/

\a

R

nIj

)\

PLASTIC BAG1T

k

2 m

T

STEEL

I

TUBE

1 ,0.03 m[

I)

CONCRETE SLAB

\

1111

]1

I filio.e m1

/ \

.38 m

\

i

O.0G m

1

IGNITION\

S

U

3 m H~"~ ! 2

SKETCH OF TEST CONFIGURATION WITH PHOTOGRAPH

7 0H

"S 5.0 -\B

P

i.o H

OETOMATION: 1670 m/s

0.5 1.0

DISTANCE (m)

TRAJECTORIES OF THE FLAME AND DETONATION FRONTS

Part IV: Tubes

TABLE AIV - Fuel-Air Flame Accelerat ion: Tubes



Remarks

i) Weak Ignition:

A4.1 Chapman and Wheeler (1926)

A4.2 Wagner (1982)

A4.3 Bartknecht (1981)


A4.5 Phillips (1982)

A4.6 Chan et al. (1981)

A4.7 Moen et al. (1982)Hjertager et al. (1984)Hjertager (1984)

2.4 m long x 50 mm diametertube with repeatedorifice plate obstacles

0.45 - 1.22 m long, CH^63 and 152 mm diameterOrifice plate obstacles(see Fig. A4.6)

10 m long x 2.5 m diameter CHMtube with orificeplate obstacles(see Fig. A4.7)

C3 H8

420

2.5 m long x 40 mm diametertube with repeated plateorifice obstacles(see Fig. A4.2)

10 m(see

longFig.

x 1.6 m diameterA4.3)

30 m long x 0.4 m diameterNo obstacles(see Fig. A4.4b)

17 m long rough tube

C3 H8

CH

S *

770

200

1402002000

1100150

550

3.9

12

0.2

10.9

Open both ends

Ignition closed end,other end open

other end openother end openDetonation

300-500

650

4

13

.0

.9

Ignition end closed,other end open

TABLE AIV Continued.., Il



Remarks

A4.8 Lee et al. (1984) 11 m long, 50 mm diameter Htube. Orifice Plates (OP) BR=0.44 0Por Shchelkin Spirals (SS) BR=0.6 OPfor initial 3 m. BR=0.44 SSBR = Blockage Ratio(see Fig. A4.8)

Transition to detonation 17ï<H2<45%Transition to detonation 30%<H2<33XTransition to detonation 17%<H2<45%

A4.9 Chan et al. (1984) Longer than 11 m, 50,150 and 300 mm diametertubes. Orifice plateobstacles first 3-5 msection (see Fig. A4.9)

C2H2

C3 H8

Transition to detonation % ?in 300 mm tube; 21%, 26% in 150, 50 mmtubes respectivelyTransition to detonation %C2H2>5.5%in 50 mm tube1000 m/s in 5 cm tube800 m/s max in al l tubes600-800 m/s max in a l l tubes

A4.10 Chan et al. (1985)

ii) Jet Ignition;


14 m long, 150 mm diametertube, 4.5 m orifice plateobstacle section. 11 mlong, 50 mm diameter tube3.0 m orifice plate obstaclesection (see Fig. A4.10)

Into 30 m long pipelines;100, 200 and 400 mm. Noobstacles (see Fig. A4.11)

C2H2

H2C 3 H

Transition to detonation XC2H2>4.75%

Transition to detonation %C2H2>5.75%

Transition to detonation

Transition to detonation %H2>16%

Transition to detonationTransition to detonationTransition to detonation

TABLE AIV Continued... /3

Item Reference Configuration Fuel Flame Overpressure RemarksVelocity MaximumMaximum (bar)(m/s)

A4.12 Wagner (1982) 40 mm diameter driver CH — 1.5section into 40, 80, 160 C2H1+ 2.5200, 300 mm diameter tubes C,H2 540 and 80 mm tube H2 7(see Fig. A4.12) CS2 2.5

A4.13 Eckhoff et al. (1980) 0.5 m diameter driver with C H8 500 2.5acceleration plates into10 m x 2.5 m diameter tube(see Fig. A4.13)

Figure A4.2Wagner (1982)

Repeated o r i f i c e plates in 2.5 m long, 50 irm diameter tubeCH4

4P

12

10

e

6

2

[bar]

/

• * • * — — — * ~

S* r

Orifice Number

10 15 19

Maximum Pressure for 3 cm Diameter Orifice withDistance of 10 cm; S cm; 2. S cm

Figure A4.3Bartknecht (1981)

10 m long x 1.6 m diameter tubeNo obstacles

— ignition at open end

length of pipe I

Pipeline with nominal diameter 1,600 mm, I = 10 m. The course of propaneexplosions (4,25% CjH8 in air)


30 m long x 0.4 m diameter tubeNo obstaclesH2> C3H8 and CH4

S- «00

iOO

200

1.2ï/I

pipeline closed at one endignition at closed end

length of pipe I

Influence of the nature of the flammable gas on the course of explosions inpipelines

Explosion velocities of flammable gases in a pipeline <t> 400 mzi.l = 30 m,one end open/completely closed. Ignition at zero turbulence by spark gip

Pipeline

Flammable gas

MethanePropaneHydrogen

one end open

vmax(m/s)

140200

2,000

vex: end of pipe(m/s)

140200

2,000

both ends

vmax(m/s)

36125

2,000

closed

vel: end of pipeim a

313 :

2.000

Orifice plates0.45 - 1.22 m long tubes63 and 152 mm diameterCH4


• Viy

ScX-Up

L-'0 = 12 0 , P/h'8 2

1./Q' 12 0 , P/fi- 10-9

02 04 06 OS iO 12

NORMALIZED DISTANCE TRO« tCNi7)0N , x / t

ovcrpr<s»u7*« otfiw-r-ncrf at various positions(x/L! in tub*» of different length to diamattrratio •


Hjertager et a l . (1984)Hjertager (1984)

10 m long x 2.5 m diameter tube with o r i f i c e plate obstaclesC3H8 and CH4

1SMITI0M/ ( > • 0)

i i

SOUKLE

1

r - p

aiFICE.

1

—1

•UTEJ'

1

t1

1 1

1 Ï 1

TD

1

D • 2 . 5 i

9 plat** ( p ' l a ) ; x = 1.43. 2 . b } . 3 . (S , 4.6S. Î .65 ,

i •!<[>• <p • 1.5a): » • 1.45. 3 .15 . *-»5, 4 .15 . 7.45,

5 a l a i » (p " Ja); « « 1.45. 3 .45 . 5.45. 7.45, 9.15»

4 plaies (p = 2.5a); s e 1.45, 4 .15 , 4.45. 9.15a

3 r l i u i : » = 1 .45. 5 .13 . 1 .33-

!

h •

<¥>

o.w

0.4

0.75a

0.5

0.71

0.37a

0.3

D . U

0.30a

0.14

0.92

O.lB

Schematic *mgnm iUuiimtlng obiudt conr«urai»at ta ih* optotior tubeTW i«ul tituac* fitMH UM nnniM •*>••«• m MM «y*» M « af » • nh« ta » f M.

Figure A4.7 Continued.,.

— 500

o£3 «00

Ï 300

i

BLOCKAGE RATIO, BB i

0.1

EMPTY TUBE. POINT ICNITION

_I | |1

. Peak overprauur* inude the lube at function of nvimbei of tint» fix biocka)ntuttBR - 0 . 1 6 , 0.3 and 0.5. Proptn*—air mUturaa.

NUMBER OF RINGS

Terminal Dune ipced (between * , " 6.6l m nnd x ( • 9.61 m) versus number ofriaf» lor vanoua bktckafe ralWM. PropsiM—*ir a i t t u n i

IWUH OVERPRESSURE I b l r )

il

5 S

jr

Ir 0

AVERAGE MAXIMUM OVERPRESSURE (b»r|

s ; S3

-

1 1

szn

1 '

ï 1

î 1>

_ P

RO

PA

NE

.Q

U3a-i

>•F»

OO3

3

(T>C L

Figure A4.8Lee et a l . (1984)

11 m long, 50 mm diameter tube;Orifice plate orShchelkin spirals for initial 3 m

- I T r » _ i i i " t^ j -

IS C * « * M U C é ù p i m W u

CONSTANT VOLUME

- O - SMCMCLMIN I P I I U L , • « • 0 - 4 4

- O - oniricE HiMot, i » « a * 4- 9 - ORIFICE RtN*l, M'D.tO

10 IS 20

Variation of thr maximum iteady-iuie flamr wlociiy with compouiion of themaure for the thiac oUiack array conHfuretxHu nu4wd

Variation of ihc maximum -nw\ pi enure with compos Don of the Hj-*u mixIUIC foi the thjM OIHTKIC «ri»y conTtfuiationi nudied.


Variai*» of fame wlodly aloof Ih* b in* tuto fat the orilk» rtnf obpuck•my "it* • UDCkap ntio BR - 0.60.

Figure A4.9Chan et a l . (1984)

11 - 14 m long tubes 50, 150 and 300 mm diameter,Or i f i ce plate obstaclesH- > C 3 H 8 ! and

2000

1500

ELCO

Id

2

U-

Z 1000sx

5 0 0

—i 1—;—i r

ORIFICE OBSTACLE

D

ISOBARICSOUND SPEED

I

5 cm TUBE B.R.-0-4415 cm TUBE B.R.- 0-39

30 cm TUBE B.R.- 0 2 8

10 15 20 25 30

% H2 IN H 2 - AIR

35 4 0 45

MAXIMUM FLAME SPEED - m/ltc

U3C

Oo


o

24

100

flOO

6 0 0

4 0 0

200

1

C j H , - AIR

ORIFICE OBSTACLE

A

? •-D 1 8

'?4 40

* • •

• • • • "

0S9

A

A A1

0 0

1

4

— 1 —

-

OAoA

A

AA

1

• . , ^

X

- 0 — TUBE

- Û - TUBE

- O - TUBE

1

1

ISOBARICSPEED

DIA D- 5cm

DIA 0> IS cm

01A D-SOcm

1

SOUND

8R-

BR.

BR>

0-

0-

0-

-

-

44

39

28

-

0-6

2 5

08 10 I'Z 1-4 1-6

EQUIVALENCE RATIO - <f>

I I I I I I I3 0 Ï 5 4 5 5 0 9-5 -6 -0 es TO

Figure A4.10Chan et al. (1985)

14 m long, 150 inn diameter and 11 m long, 50 irm diameter tubesOr i f i ce plate obstacles near i gn i t i on endH2, C2H2 and C2H4

H,-AIRTUBE DIA. -- 5 en

£UUU

5 0 0

1000

5 0 0

•

O

o

D

D

D

Dy

Po

D

O

D O '

>

°

O

° •

DD

o £

<^o '•

—DD D

>ii

o]/

o

D

O

o •

— TERMINAL VELOCITY. IN. ROUGH TUBE

— .FINAL VELOCITY . IN• ' '•- SMOOTH TUBE

1

10 20 ' -3O

H, CONCENTRATION , 7.

AO

Terminal Velocities and Final Velocities for H,-Air Mixturesin a Rough and » Snooth 5. cm Tube, Respectively ,


2000 r

e '• 1500

5% CtH,-AIH

TUBE OIA. = 5 cm

2

1000

500

OBSTACLE SECTION

0: ' • 2 • 4 •' 6 • 8 10. . 12

DISTANCE'"'FROM IGNITION , m

Flame Velocity vs. OisUnce from Ignition for 51 C?l^-Air Mixtures in i 5 cm lube

C.Hj-AIRTUBE DIA. = 5 cm

2000

1500

uO

<_ J

1000'

500

•OBSTACLE SECTION

4 . . • • 6 • • : - . ' . 8 .

•DISTANCE FROM IGNITION , . m

12.

. . FUrne Velocity vi. Distance, from Ignition for Various CjH -Air Mixtures In t 5 cm Tube


e.

>-t—

LO

CI

>

Z

_l

2000

1500

1000

0• 0

a

V

00

. •

C.H,.- AIR

TUBE DIA. = 15 cm

- 3.50 %

- 3.75 % .

- 4.00 %

- 4.25 %

- 4.50 %

- 4.75 %

- 5.00 %

- 5 . 2 5 % . , _ _

.

_

500

' OBSTACLE SECTION/ / / / / • / • ' / M / / I

o . . ; . 2 • . 4 • : }'&• ' • • s. ' i o

' . DISTANCE F R O M ' IGNITION ', m

12

Flame Velocity vs. distance from ignition for various CjHj-Air Mixtures in i 15 en tube


Jet ignition into 30 m long pipelines100, 200 and 400 mm diameterNo obstaclesH, and

("V,]

JS KD

Itar]

D 20

length of pipelne 1

M

lbo-1

01

y

O » [m]

length ot pipeline I

The course of combustion of turbulent gas/air mixtures in pipelines closed atone end. Ignition by flame jet

Pipe length for acceleration to detonation, fordifferent turbulent gas/air mixtures ignited by flame jet

Flammable gas

MethanePropaneHydrogen

Diameter of pipeline

100

12.512.57.5

Pipe lengthdetonation

200

18.517.512.5

in m forvelocity

(rnm)

400

>3022.512.5

acceleration to

Figure A4.12Wagner (1982)

Je t ignition from 40 mm diameter driver section into 40, 80, 160, 200 and300 mm diameter tubes

r,v.

• t-^zùrun pressui-c daLf.slrean cf the orifice forstcichic-.ctric ei'rwler-air niziures end différer.: :uconbiruztions. The diameters of ihe dour.z'.reem tubeere shoun in the figure.

g

0

8

e

L

2

ICH.

iCrto! o„ Zô7é"ôT»

- X

|C

rD• 1 *

i •

H i |CS 1

O £.• 1 A "

o /

HîLzimm pressures for etoichionctric fuel-air mixtureses c function of the Lsninar flams velocity r of thefuels given on the top of the figure. The tube combinetions ere: driver gee tien 40 ran dicnclcr; dounstrear:section 40 or 80 m\ diameter respectively.

ûp(bor)10

— 500/Jt/SOO— ?QOt 1/200— eo/x/80

fkLzirruti overpressure for stoichionciric propene-eirmixtures as a fune lien of Fo/Fg. The tube combinationsere giver, in the picture. X is the diencter of theorifice.

Figure A4.13Eckhoff et a l . (1980)

Jet ignit ion from 0.5 m diameter driver with acceleration plates into10 m long by 2.5 m diameter tube

i.o i.o 1. i . o I. -i.o I i.o \ A.o i. t o

AIRJNLET

15.-sa

2 m

790750 GAS EXPLOSION TUBE


2000

1000

500

200

•100

50

20

10

-

\ O

\

~ A

N \

- \ N

-

PRESENT

O " 12

A - 7

• - o

\

D \

EXPERIMENT,

ACCELERATION

% -

CLASSICAL

VENTING MODEL

S = a S 0

SQ= 0 , 6 0 m/s

, , ,

JET INITIATION

PLATES

-

O

—

A ^ \O

A^A

•a

0,2 0,4Area Ratio

0 , 6 0,8 1.0

Figure A4.13 Continued.,

A

0,5 -

X

0,2 .

JET INITIATION

O PRESENT" EXP. 12 ACCELERATING PLATES

A " " 1Q " 0

D

WAGNER et.al.26'27 C,H,,-AIR

0,10,2 0,4

Area Ratio

0,6 0,8 1,0

ANNEX B

FLAME ACCELERATION AND TRANSITION TO DETONATIONIN LARGE FUEL-AIR CLOUDS WITH OBSTACLES

by

I.O. Moenand

A. Sulmistras

UNCLASSIFIED

DEFENCE RESEARCH ESTABLISHMENT SUFFIELDRALSTON, ALBERTA

SUFFIELD MEMORANDUM NO. 1159

Flame Acceleration andTransition to Detonation

in Large Fuel-AirClouds with Obstacles

1.0. Moen

and

A. Sulmi stras*

PCN NO. 77C5O

February 1986

* Mechanical Engineering Department,Concordia University,

Montreal, Quebec

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ABSTRACT

The results of a series of flame acceleration tests performed at the Defence

Research Establishment Suffield (DRES) are reported. These tests were performed

in order to assess the potential for flame acceleration and transition to

detonation in simulated industrial environments with repeated obstacles. The

experimental apparatus consisted of a channel 1.8 m x 1.8 m in cross-section and

15.5 m long, connected to a 0.9 m diameter tube, 8 m long. The bottom of the

channel was confined by the ground, and the sides were confined by plywood or

plexiglass sheets. The only top and end confinement was due to the plastic

envelope which was used to seal the configuration to contain the explosive

gaseous mixture. Two obstacle configurations were tested, corresponding to

500 mm or 220 mm diameter tubes mounted across the channel at regular intervals.

Tests were performed with acetylene, propane and hydrogen sulphide fuels

mixed with air. For near stoichiometric acetylene-air, the flame accelerates

from an initial speed of about 20 m/s up to speeds of about 400 m/s prior to the

occurrence of localized explosions which lead to the onset of detonation. With

the larger 500 mm obstacles, the localized explosion occurs at the end of the

channel and with 220 mm obstacles transition to detonation occurs 10.7 m down the

channel. One test with acetylene-air is very interesting in that ignition due to

a hot wire at the end of the channel leads to the explosion of the end-pocket of

turbulent unreacted gas. This explosion causes onset of detonation prior to the

arrival of the main flame front.

The behavior of flames in lean acetylene (5.17% C 2H 2)-, propane- and

hydrogen sulphide-air mixtures is much less dramatic. In fact, no significant

flame acceleration was observed in these mixtures. The flame speeds observed

range from about 25 m/s up to 200 m/s, with associated peak overpressures

typically less than 50 mbar. The continuous flame acceleration seen in more

confined situations is not observed in the present configuration with these

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ABSTRACT (cond't)

fuel-air mixtures. I t is concluded that in order for damaging explosions to

occur in propane- or hydrogen sulphide-air mixtures, the cloud must be: i) more

confined than in the present tests, i i ) ignited by a stronger ignition source

( i . e . , je t ignition from a semi-confined explosion) or i i i ) immersed in a denser

obstacle f ie ld than used in the present tests. On the other hand, for near

stoichiometric acetylene-air transition to detonation can be expected to occur in

obstacle environments similar to those used in the present tests.

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SPONSORSHIP

The invest igat ion described in t h i s report is part of a project to

characterize the explosion hazards of hydrogen sulphide in a i r . The pro ject is

sponsored and funded by the Atomic Energy Control Board of Canada.

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ACKNOWLEDGEMENTS

The va luab le ass i s tance o f Gayle Hal l and Chr is Brosinsky i n p lann ing and

carrying out the f ie ld t r i a l s is gratefully acknowledged. We would also l ike to

thank the personnel of the Field Operations Section, the Electronic Design and

Instrumentation Group, and the Photo Group at DRES for their valuable assistance

during the f i e ld t r i a l s .

Finally we would l i ke to thank Dr. Paul Thibault, Dr. Stephen Murray and

Professor Jaan Saber for their input through enlightening scient i f ic and

technical discussions.

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TABLE OF CONTENTS

Page

ABSTRACT i

SPONSORSHIP i i i

ACKNOWLEDGEMENTS i v

TABLE OF CONTENTS . . . v

LIST OF TABLES vi

LIST OF FIGURES v i l

1. INTRODUCTION 1

2. FLAME PROPAGATION AND ACCELERATION 2

3. EXPERIMENTAL DETAILS 5

4. EXPERIMENTAL RESULTS 7

4.1 Summary of Results 7

4.2 Data Analyses 7

4.3 Acetyl ene-Ai r Results 8

4.4 Propane-Air Results 11

4.5 Hydrogen Sulphide-Ai r Results 12

5. DISCUSSION 13

6. CONCLUSION 15

7. REFERENCES 17

TABLESFIGURES

APPENDIX A TABULATED PRESSURE RECORD RESULTS

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LIST OF TABLES

TABLE I Combustion Properties of Selected Stoichiometric Fuel/Air Mixtures

TABLE I I Summary of Flame Acceleration Tests

A. 500 mm Obstacles

B. 220 mm Obstacles

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LIST OF FIGURES

FIGURE 1 Theoretical correlation of maximum overpressure vs maximum flame

speed for constant velocity flames in spherical and planar

goemetries.

FIGURE 2 Aerial view of test site.

FIGURE 3 Selected photographs of channel with 500 mm diameter obstacles.

a) Side view of channel

b) End view of channel

c) Obstacles: end view

d) Obstacles: side view

FIGURE 4 Side view of channel with 500 mm diameter obstacles.

FIGURE 5 Selected photographs of channel with 220 mm obstacles.

a) Obstacles: end view

b) Obstacles: side view

FIGURE 6 Side view of channel with 220 mm diameter obstacles.

FIGURE 7 Flame propagation in acetylene-air 17.8% C2H2) with 500 mm diameter

obstacles and spark igni t ion.

a) Maximum pressure and flame velocity vs distance from pressure

records

b) Time of arr ival vs distance from high-speed films

c) Velocity vs distance from high-speed films

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LIST OF FIGURES (cond't)

FIGURE 8 Flame propagation and transit ion to detonation in acetylene-air

(7.71% C2H2) with 220 mm diameter obstacles and spark igni t ion.

a) Maximum pressure and flame velocity vs distance from pressure

records

b) Time of arrival vs distance from high-speed films

c) Velocity vs distance from high-speed films

FIGURE 9 Selected frames from the 90° wide high-speed f i lm record showing

flame acceleration and transit ion to detonation in acetylene-air

(7.71* C2H2) with 220 mm obstacles and spark ign i t ion.

FIGURE 10 Pressure-time histories at various positions down the channel for

7.71* C2H2 with 220 mm diameter obstacles and spark igni t ion.

FIGURE 11 Igni t ion, flame acceleration and transit ion to detonation with

acetylene-air in a 1.8 m x 1.8 m lane, 15.5 m long.

FIGURE 12 Flame propagation in acetylene-air (7.5% C2H2) with 500 mm diameter

obstacles and spark igni t ion.

a) Maximum pressure and flame velocity vs distance from pressurerecords

b) Time of arr ival vs distance from high-speed filmsc) Velocity vs distance from high-speed films

FIGURE 13 Selected frames from the 30° high-speed f i lm record showing the

explosion and transit ion to detonation in the turbulent end-pocket ofacetylene-air prior to the arr ival of,the main flame front.

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FIGURE 14 Flame propagation in acetylene-air (5.17% C2H2) with 220 mm diameter

obstacles and spark i g n i t i o n .

a) Maximum pressure and flame ve loc i ty vs distance from pressure

records

b) Time of a r r i va l vs distance from high-speed f i lms

c) Velocity vs distance from high-speed f i lms

FIGURE 15 Two frames from the 90° t e l e high-speed f i l m record showing the flame

p r o f i l e towards the end of the channel i n lean acety lene-air (5.17%

C2H2) wi th 220 mm obstacles.

FIGURE 16 Flame propagation in propane-air (4* C3H8) wi th 500 mm diameter


a) Maximum pressure and flame ve loc i ty vs distance from pressure

records

b) Time of a r r i va l vs distance from high-speed f i l m

c) Velocity vs distance from high-speed f i l m

FIGURE 17 Flame propagation i n propane-air (4.14% C3H8) wi th 500 mm diameter

obstacles in the center only and spark i g n i t i o n . Maximum pressure

and flame ve loc i ty from pressure records.

FIGURE 18 Flame propagation in propane-air (3.95% C3H8) with 500 mm diameter

obstacles and tube i g n i t i o n . Maximum pressure and flame ve loc i ty

from pressure records.

FIGURE 19 Flame propagation in propane-air (4.32% C3H8) wi th 220 mm diameter


a) Time of a r r i va l vs distance from high-speed f i lms

b) Velocity vs distance from high-speed f i lms

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FIGURE 20 Flame propagation in propane-air (4.05% C,Ha) with 220 ram diameter

obstacles and tube igni t ion. Maximum pressure and flame velocity


FIGURE 21 Pressure-time histories at various positions down the channel for

4.05% C3H8 with 220 mm diameter obstacles and tube igni t ion.

FIGURE 22 Two frames from the 90° wide high-speed f i lm record showing flame

propagation in a propane-air mixture with 220 mm obstacles and spark

igni t ion.

FIGURE 23 Flame propagation in hydrogen sulphide-air (9.3% H2S) with 500 mm

obstacles and tube igni t ion. Maximum pressure and flame velocity


FIGURE 24a) Flame propagation in hydrogen sulphide-air (12.9% H2S) with 500 mm

diameter obstacles and spark igni t ion. Maximum pressure and flame

velocity from pressure records.

FIGURE 24b) Pressure-time histories at various positions down the channel for

12.9% H2S with 500 mm diameter obstacles and spark igni t ion.

FIGURE 25a) Flame propagation in hydrogen sulphide a i r (10.7% H2S) with 220 mm

diameter obstacles and tube igni t ion. Maximum pressure and flame

speed from pressure records.

FIGURE 25b) Pressure-time histories at various positions down the channel for

10.7% H2S with 220 mm obstacles and tube igni t ion.

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DEFENCE RESEARCH ESTABLISHMENT SUFFIELD

RALSTON, ALBERTA

SUFFIELD MEMORANDUM NO. 1159

Flame Acceleration and

Transition to Detonation

in Large Fuel-Air

Clouds with Obstacles

by

I.O. Moen

and

A. Sulmi stras

1. INTRODUCTION

Explosions resulting from the accidental spill of a variety of fuels have

occurred with increasing frequency over the past twenty years, sometimes with

devastating consequences. It has therefore become necessary to realistically

assess the potential explosion hazards associated with accidental spills of fuels

in chemical and industrial plant environments. Typically, the spill will occur

within the plant itself, in a complex obstacle configuration involving arrays of

pipes, conduits and pipe racks, as well as buildings and other confining

structures. It is known that such obstacles can have a dramatic influence on the

flame propagation through the fuel-air cloud which is produced by the mixing of

the spilled fuel with the surrounding air. In fact, it is the presence of these

obstacles and confining spaces which is thought to be responsible for producing

violent combustion and potentially damaging blast waves.

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A wide variety of experimental tests, both large and small scale, have been

performed so that there is now a considerable data base available on fuel-air

explosions and the blast waves produced by such explosions. The results of these

tests have recently been summarized by Moen and Saber (1985). Based on these

results, particularly hazardous obstacle configurations can be identified as

those whic( c^e heavily confined. In tubes, pipes and confined channels, for

example, high flame speeds and potentially damaging pressures are reached within

less than four diameters, even for insensitive mixtures of methane and air

(Moen et al., 1982). Similar flame acceleration is also observed in clouds which

are confined on top and bottom over a large area (Zeeuwen and van Wingerden,

1983; Moen et al., 1981; and Hjertager, 1984). Such clouds could be produced by

a release into an area within a plant which is covered by a roof. Explosions in

confined spaces can also serve as strong ignition sources for an external cloud,

thus enhancing the potential for violent explosion or even transition to

detonation in this cloud (Schildknecht et al., 1984). Weak spark ignition of

such a cloud in a relatively unobstructed environment is unlikely to result in a

damaging explosion, even for relatively sensitive fuels such as acetylene and

hydrogen (Lind and Whitson, 1977; Schneider and Pfôrtner, 1981; and

Brossard et al., 1985).

In partially confined regions with obstacles, which are more typical of

chemical plants, the flame acceleration is less dramatic than in heavily confined

regions and depends critically on the degree of confinement, the obstacle

configuration, the ignition source and the fuel-air mixture. In view of the

complexity of the coupled chemical and fluid-dynamic processes involved in the

propagation and acceleration of flames in obstacle environments, the nature of

such explosions cannot yet be predicted theoretically or numerically, so that

experimental tests in configurations which simulate the chemical plant

environment are required in order to assess the potential for hazardous

explosions.

The present paper reports on an experimental investigation of flame

propagation in a partially confined channel with repeated obstacles. The aim of

this experimental study is to assess the potential for flame acceleration in

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configurations which simulate a chemical plant environment with arrays of pipes

in the fuel air cloud. Tests were performed with repeated cylindrical obstacles

of two diameters (500 and 220 mm) for fuel-air mixtures based on acetylene,

propane and hydrogen sulphide fuels covering a wide range of mixture

sensitivity.

Some of the background on flame propagation and acceleration which provided

the more fundamental motivation for these tests is described in Section 2. The

experimental details are described in Section 3. Results, including flame

velocities and pressures at various positions along the channel, are described in

Section 4. Comparison with results from other investigations and îiscussion of

the results are given in Section 5, and the implications of the results for

explosion hazards evaluation are discussed in the conclusion.

2. FLAME PROPAGATION AND ACCELERATION

Deflagrations or flames are expansion waves in which both the pressure and

density decrease across the wave front. A combustible mixture is characterized

by its laminar burning velocity, S., which depends on the transport properties

and the reaction rate. Typical burning velocities for selected fuel/air mixtures

at stoichiometric compositions are given in Table I. Except for highly reactive

fuels (i.e., C2H2) and mixtures with high transport rates (i.e., H 2 ) , the laminar

burning velocity for fuel/air mixtures is about 0.5 m/s. The expansion across

the flame reaction-zone will generate a flow velocity, U, ahead of the flame, so

that the observed flame speed is U + S,. For flame speeds much less than the

sonic speed in the unburned mixture, the pressure drop across the flame can be

neglected. The density ratio (Pl/p2) across the flame in this approximation is

between 6 and 8.5 for the stoichiometric fuel-air mixtures included in Table I.

The corresponding laminar flame speeds, calculated assuming zero velocity of the

burned gas, is given by Pi/p2 \> These laminar flame speeds are also given in

Table I. For the test performed in the present test series the laminar flame

speeds range from 12.1 m/s for stoichiometric acetylene/air to 1.5 m/s for lean

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hydrogen sulphide/air. The pressures produced by such flames are much too smallto cause any blast damage.

The pressure produced by constant velocity flames has been calculated by

several investigators (Kuhl et al., 1973; Guirao et al., 1976; Lee et al., 1976

and Strehlow et al., 1979). Typical calculated results for fuel-air flames in

planar and spherical geometries are shown in Figure 1. From these results it can

be seen that flame velocities in excess of 120 m/s (70 m/s) are required in

spherical (planar) geometry to produce pressures above 150 mbar, which is the

approximate threshold for major structural damage (Baker et al., 1983).

Considerable flame acceleration must therefore occur, even in acetylene/air

mixtures, in order for damaging blast waves to be produced. Such flame

acceleration has been observed with repeated obstacles in tubes, in confined

channels and in clouds confined between two solid surfaces (Moen, 1982). In

these configurations, a positive feedback mechanism is established whereby the

turbulence produced by the flame-induced flow over the obstacles increases the

rate of burning, which in turn increases the flame induced flow and turbulence,

thus further enhancing the rate of burning. This feedback mechanism can lead to

the continual acceleration of the flame in a repeated obstacle environment

(Moen et al., 1981).

The strength of the positive feedback mechanism depends on the geometry, the

obstacle configuration, the degree of confinement and the fuel-air mixture.

Laboratory experiments in channels with repeated obstacles have shown that if one

of the sides of a channel is even partially open, the acceleration of the flame

is reduced dramatically (Chan et al., 1983). The present test series was

designed to study the acceleration of flames in channels open on the top with

repeated obstacles, in order to assess the potential for flame acceleration in

simulated chemical plant environments on a larger scale and for various fuel/air

mixtures. The fuel/air mixtures were chosen to cover a wide range of laminar

flame speeds as well as detonation sensitivity. The critical tube diameter of

the mixtures range from 0.115 m for stoichiometric acetylene/air to an estimated

value of 3.5 m for lean hydrogen sulphide/air mixtures. The critical tube

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diameter, the minimum detonation energy and the detonation velocity for selected

stoichiometric fuel/air mixtures are included in Table I for comparison.

3. EXPERIMENTAL DETAILS

The experimental test series was performed at the DRES fuel-air facility.

An aerial view of the facility showing the test pad, instrumentation and

fuel-flow control trailers, and high-speed camera shelters is included in

Figure 2. The facility, which is described in detail by Funk et al., (1982), is

centered around a 18.3 m x 7.6 m concrete test pad onto which the experimental

apparatus can be mounted. For the present tests, the test section consisted of a

channel, 1.8 m x 1.8 m in cross-section and 15.5 m long, constructed with a

support frame of aluminum tubing 60 mm in diameter. The sides of the channel

were confined by plywood or plexiglass sheets and the bottom was confined by the

pad itself. The plexiglass and plywood sheets were hinged to the frame in such a

manner that they would swing out prior to being destroyed by the explosion. The

only top confinement was due to the plastic envelope which enclosed the channel

and joined it at one end to a 0.9 m diameter tube, 7.6 m long. The configuration

was sealed to contain explosive gases by a plastic sheet at the end of the tube

and by wrapping the plastic around an inlet pipe at the end of the channel. Side

and end views of the channel, wrapped in the plastic envelope, are shown in

Figure 3a and b, respectively. Two obstacle configurations were tested,

corresponding to 500 mm and 220 mm diameter tubes mounted across the channel at

regular intervals. Photographs illustrating the 500 mm obstacle configuration

are shown in Figure 3c and d. A sketch illustrating this obstacle configuration

is shown in Figure 4. The corresponding photographs and sketch for the 220 mm

obstacles are shown in Figures 5 and 6, respectively. As seen in Figures 3d

and 5b, both the 500 and 220 mm obstacles were hollow pipes which were not sealed

at the ends. During the tests these obstacles therefore also contained explosive

mixture. The obstacles were mounted at regular intervals in Sections 2-11,

inclusive, with no obstacles in the first or last section of the channel, as

illustrated in Figures 4 and 6.

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Tests in each obstacle configuration were performed with acetylene (C^H2),

propane (C;jHb) and hydrogen sulphide (H2S) fuels mixed with air. The test gases

were mixed with the initial air in the test volume by a multipath recirculation

system using a high-capacity centrifugal blower. The composition and mixture

homogeneity in the test volume were monitored by continuously analyzing samples

taken from two ports in the channel and one port in the tube. The maximum

uncertainties in fuel concentrations in the test volume for the different fuels

were +0.25% H2S, +0.05% C 2H 2 and +0.05% C3Ha, respectively.

Once the desired fuel-air composition had been attained, ignition of the

flame was achieved either at the far end of the tube by one spark or by four

sparks mounted across the channel at the tube end. The latter form of ignition

was used to simulate line ignition which would produce approximate

two-dimensional flame propagation and flow down the channel. The total energy

{h CV2) supplied to the four sparks was 8.4 Joules. In selected tests, the

plastic confinement at the end of the channel was removed just prior to ignition

using a hot wire to cut the plastic envelope.

The arrival and pressure profile of the wave were monitored at up to ten

positions along the bottom of the channel by piezoelectric pressure transducers.

The positions of these transducers are shown in Figures 4 and 6. In selected

tests, two pressure transducers were also mounted in the tube. Three high-speed

cameras (~3000 frames/sec) were used to record the flame propagation down the

channel. Two cameras were placed 90° to the channel axis, one providing a view

of the whole channel (90° WIDE) and the other providing a more detailed view of

the last 8 m of flame propagation (90° TELE). The third camera was placed at a

30° angle to the channel axis giving a different view of the flame propagation.

Since hydrogen sulphide and the main product of combustion, sulphur dioxide,

are both highly toxic, the special safety procedures developed during previous

critical tube diameter tests (Su!mi stras et al., 1985) were followed in carrying

out the tests involving H2S.

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4. EXPERIMENTAL RESULTS

4.1 Summary of Results

The experimental results from the twelve tests performed are summarized

in terms of average and maximum flame speeds, and peak overpressures in Table II.

From this table it can be seen that the only potentially damaging explosions

observed were those associated with transition to detonation in near

stoichiometric acetylene-air mixtures. The behaviour of flames in lean acetylene

(5.17%. C 2H 2)-, propane- and hydrogen sulphide-air is much less dramatic. In

fact, no significant flame acceleration was observed in these mixtures. The

flame speeds ranged from about 25 m/s up to 200 m/s, with associated peak

overpressures typically less than 50 mbar. Although, the maximum flame speeds

observed were 15-20 times the laminar flame speeds, the continuous acceleration

observed in more confined situations is not observed in this configuration with

these fuels.

4.2 Data Analyses

More detailed results from each test are given in Figures 7-25. Theseresu l t include peak overpressures and velocities obtained from the pressurerecords, and time-of-arrival and velocity data obtained from the high-speedfilms. Frames from the high-speed film records and pressure-time histories arealso included for selected tests. The peak pressures, flame time-of-arrival andvelocity data obtained from the pressure records are tabulated in Appendix A.The time-of-arrival of the flame is assumed to coincide with the peak inpressure, typically observed just prior to the decay into a negative pressurephase which indicates that the main flame front has passed. The time-of-arrivaland velocities obtained in this manner are in good agreement with those obtainedfrom the high-speed film records. Unfortunately, analysis of the high-speed fi lmrecords was only possible for the tests with acetylene and for selected testswith propane. In H2S/air mixtures the flame was not visible, so that the flamedevelopment was obtained solely from the pressure records.

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The high-speed film records obtained from the two 90° cameras (90° WIDE

and 90° TELE) were analyzed by monitoring the time-of-arrival of the leading

flame front vs position along the channel, and the flame velocity was deduced

from this data. Although the flame zone was observed to be wrinkled, folded and

relatively thick, the flame was observed to propagate as a thick turbulent flame

brush extending from the bottom to the top of the channel (see Figures 9, 11, 15

and 22). Except for local variations in the velocity of the leading front as it

propagates around the obstacles, the flame velocity reported corresponds to the

velocity of this flame brush.

The venting out the top as the plastic was torn and the motion of the

plywood and plexiglass side confinement were also observed on the high-speed

films. In the acetylene/air tests with transition to detonation, the plastic top

was removed before the arrival of the flame and the sides were blown out some

distance after the flame front, thus providing complete top venting and some side

venting of the burned gases (see Figures 9 and 11). In all the other tests, the

tearing of the plastic coincided approximately with the arrival of the flame, and

the sides either remained intact or blew-out long after the flame had passed (see

Figures 15 and 22). Complete side confinement with top venting of the burned

gases can therefore be assumed in these tests.

4.3 Acetylene-Air Results

Tests with stoichiometric acetylene/air were performed in the two

obstacle configurations. In both cases, the flame continuously accelerates down

the channel and reaches a speed between 250 and 400 m/s prior to the occurrence

of a localized explosion and the onset of detonation. With the larger 500 mm

obstacles (Figure 7), the flame appears to propagate in a sporadic manner through

the obstacle field (Figure 7c). This is due to the jetting of the flame as it

propagates between the obstacles and the slow-down of the leading flame front in

the wake of the obstacles. The general trend is for the flame to accelerate.

This acceleration is particularly dramatic during the last 7 m of propagation.

The flame reaches the end of the channel with a velocity of about 400 m/s, at

which time a localized explosion near the bottom of the channel triggers

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detonation of the remaining unburned mixture. The peak pressure reaches about

150 mbar at 2 m. Similar peak pressures are recorded out to 4 m, beyond that the

records are off-scale indicating pressures larger than 150 mbar.

For stoichiometric acetylene/air with the smaller 220 mm obstacles,

transition to detonation occurs about 10.7 m down the channel, again due to a

localized explosion at ground level. The development of the flame is

characterized in Figure 8. Notice that the flame speed reaches about 250 m/s

prior to a rapid acceleration phase which starts 9 m down the channel and results

in a full-fledged detonation with a velocity close to 1800 m/s at about 13 m.

Selected frames from the 90° wide high-speed film record showing the flame

propagation and transition to detonation are included in Figure 9. The first two

frames (Frames a and b) show the flame during the rapid acceleration phase. In

Frame c, a localized explosion can be seen at ground level. The growth of this

explosion seen in the next two frames (Frames d and e) results in the detonation

shown in Frame f. The pressure-time histories at various positions are shown in

Figura 10. Prior to the rapid acceleration phase, the peak pressure is less than

2 bar. The peak pressure quickly increases to detonation pressure of almost

15 bar at 10.6 m.

The two tests described above illustrate the classic mechanism of flame

acceleration in an obstacle environment, with localized explosions somewhere in

the turbulent flame brush leading to the onset of detonation (Lee and Moen, 1981;

Urtiew and Oppenheim, 1966). The test with 7.5% C2H2 (Test #14) illustrates

another mechanism for transition to detonation. In this test, ignition of the

turbulent pocket at the end of the channel by the hot wire used to cut the end

plastic, leads to transition to detonation prior to the arrival of the main flame

front. The phenomena involved are illustrated by the sequence of photographs

shown in Figure 11. Ignition by four sparks at the tube end at 0 ms produces a

flame which propagates down the channel as shown in the next five frames

(25-125 ms). Ignition at the far end of the bag due to the hot wire occurs at

150 ms when the main flame front is about 10 m down the channel. The burning in

the turbulent end-pocket triggers an explosion which leads to the onset of

detonation at 171 ms, at which time the main flame has reached 13.3 m. By 175 ms

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this detonation has propagated through the remaining unburned mixture, partially

destroying the apparatus as shown in the last frame at 200 ms.

The development of the main flame-front prior to the onset of

detonation is characterized in terms of peak pressure, time-of-arrival and

velocity in Figure 12. The maximum flame velocity is 180 m/s with an associated

peak pressure of 132 mbar. Such pressures are much too small for shock

reflections to be responsible for the onset of detonation. However, the

flame-induced flow produces a pocket of turbulent flow at the end of the channel.

As shown by the selected frames from the 30° high-speed film record in Figure 13,

it is the ignition of this turbulent pocket which leads to a localized explosion,

with subsequent transition to detonation. The burning in this pocket, triggered

by the hot-wire, seen in the first two frames (Frames a and b) results in the

explosion near ground level seen in Frames c and d. The subsequent detonation of

the remaining unburned mixture prior to the arrival of the main flame-front can

be seen in Frames e and f. These phenomena are similar to those observed by

Moen et al., (1985) in a 5% C2H2/air mixture, except that ignition of the

turbulent pocket is due to a hot wire rather than a flame tongue as observed by

Moen et al.

The three tests described above, which were performed with sensitive,

near-stoichiometric, acetylene/air mixtures, clearly illustrate the potential for

flame acceleration and transition to detonation given the appropriate boundary

conditions and obstacle configuration. In the present configuration, the

propagation of flames in less sensitive mixtures is much less dramatic. The

results with lean 5.17% C2H2/air are shown in Figure 14. This mixture has a

critical tube diameter of 0.5 m, almost five times larger than that for

stoichiometric C2H2/air, and a laminar flame speed less than 7.4 m/s. As seen in

Figure 14, the flame in this mixture propagates down the channel with a velocity

between 60 and 100 m/s producing an overpressure less than 55 mbar. Although

there are some fluctuations in flame velocity as the flame propagates through the

obstacle field, no continuous acceleration is observed. Two frames from the 90°

tele high-speed film record showing the flame profile in the channel are included

in Figure 15.

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4.4 Propane-Air Results

Flame velocities and pressures similar to those in lean acetylene/air

are observed in stoichiometric propane/air mixtures. The results with 500 mm

obstacles and ignit ion by four sparks are given in Figure 16. In this case, the

maximum flame speed of 62 m/s is observed about half way down the channel. By

the end of the channel, the flame has slowed down to 30 m/s. The peak pressure

of 86 mbar is observed at 1.76 m prior to the tearing of the plastic envelope.

Once the envelope is torn, allowing top venting of the burned gases, the peak

pressure remains below 30 mbar. A test with only central 500 mm obstacles gave

sl ight ly higher flame velocities of 60-70 m/s, with peak pressures less than

12.4 mbar (Figure 17). As seen in Figure 18, ignit ion at the end of the tube

with a fu l l complement of 500 mm obstacles produced a relat ively high i n i t i a l

velocity of 200 m/s in the channel. However, the flame rapidly slows down to

speeds similar to those observed with spark igni t ion. The peak pressures are

also similar to those observed with spark igni t ion. I t should be pointed out

that there are no obstacles to accelerate the flame in the tube so that speed of

the flame emerging from the tube is relat ively low. With much stronger ignit ion

by a fast flame j e t , larger flame velocities and pressures would be expected, at

least near the exit from the tube.

The results in near stoichiometric propane/air with the smaller 220 mm

obstacles for spark and tube ignit ion are shown in Figures 19 and 20,

respectively. With spark ign i t ion, the flame speed fluctuates between 55 and

90 m/s over the last half of the channel, in a manner very similar to that

observed with the larger obstacles. The flame velocities and pressures obtained

with tube ignit ion (Figure 20) again show relatively tame flame propagation with

a maximum velocity of 90 m/s and peak pressures less than 52 mbar.

The flame propagation with near stoichiometric propane/air in the

channel does not di f fer dramatically in the two obstacle configurations tested,

nor does spark or tube ignit ion produce signif icantly different results. Typical

pressure-time histories from these tests are shown in Figure 21. Notice the

build-up of pressure prior to the arrival of the flame, associated with the peak

UNCLASSIFIED

UNCLASSIFIED 12.

in pressure, and the subsequent decay into a negative phase once the flame has

passed.

The two frames from the 90° wide high-speed camera record shown in

Figure 22 illustrates the typical flame propagation observed in propane-air

mixtures. As seen in this figure, the plastic envelope tears just ahead of the

flame producing essentially complete top venting of the burned gases. The

plexiglass and plywood sides remain in place long after the flame has passed, so

that the sides of the channel are essentially completely confined during the

explosion. Similar motions of the envelope and sides are also observed for flame

propagation in hydrogen sulphide-air mixtures.

4.5 Hydrogen Sulphide-Air Results

In H2S/air mixtures the flame is not visible so that no high-speed film

analysis was possible and the flame propagation is obtained solely frm the

pressure records. The results from the three tests are presented in

Figures 23-25. Figure 23 shows the pressure and flame velocity .in a lean

9.3% H2S/air mixture, with the large 500 mm obstacles, ignited from the tube.

The flame speed is less than 50 m/s and the peak pressure of 44.8 mbar is

recorded near the beginning of the channel. Both the flame speed and pressure

begin to decrease after about 8 m and at 12 m the peak pressure is less than

3 mbar. This decrease is likely due to the increased venting of burned gas out

the top as the plastic envelope is torn. The results with 12.9% H2S in the same

obstacle configuration with spark ignition are shown in Figure 24a. In this case

the flame speed is slightly higher (40-80 m/s) and the peak pressure appears to

settle down to about 10 mbar, 8 m down the channel. The pressure records at

various positions along the channel are shown in Figure 24b. As shown in

Figure 25, similar pressures are observed with tube ignition of a 10.7% H2S

mixture in the 220 mm diameter obstacle configuration. In this case the flame

velocities appear to be a little smaller, but the peak pressures and

pressure-time histories are very similar to those observed with spark ignition.

UNCLASSIFIED

UNCLASSIFIED 13.

Although the flame speeds observed in the H2S/air tests are up to 30

times the laminar flame speed, no significant flame acceleration was observed as

the flames propagated down the channel. In fact, there is some indication that

the flame slows down toward the end of the channel. The pressures and flame

velocities observed in H2S/air are typically smaller than those observed in

C3H8/air. This is likely a reflection of the smaller laminar flame speeds

characteristic of the H2S/air mixtures (see Table II).

5. DISCUSSION

The propagation of fl i in obstacle environments with partial confinement

typical of that found r & chemical plant is a >tery complex phenomenon, involving

the interaction of the flame with the turbulent flame-induced flow around

obstacles and the pressure waves reflected from nearby surfaces. The present

tests with near stoichiometric acetylene-air mixtures clearly illustrate the

potential for flame acceleration and transition to detonation in such

environments. Although stoichiometric acetylene-air is a relatively sensitive

mixture with a high laminar flame speed, the flame in large unconfined clouds of

this mixture without obstacles reaches a maximum speed of only 35.4 m/s (Lind and

Whitson, 1977). It can therefore be concluded that the flame acceleration

observed in the present tests is due to the obstacles and the partial

confinement.

The flame acceleration observed in stoichiometric acetylene-air is analogous

to that observed with less sensitive fuels in confined channels and tubes with

obstacles (Moen 1982; Moen et al., 1982; and Hjertager et al., 1984), and in

clouds confined between two solid surfaces (Moen et al., 1981; Hjertager, 1984;

and van Wingerden and Zeeuwen, 1985). The acceleration mechanisms in this

mixture is therefore strong enough to overcome the effect of top venting of the

burned gases. For the other fuel-air mixtures tested (5.171 C2H2, C3H8 and H2S

in air) the acceleration mechanisms are overcome by the top venting and no

continuous flame acceleration is observed. Similar effects of top venting on

methane-air flame acceleration in a laboratory scale channel with obstacles were

UNCLASSIFIED

UNCLASSIFIED 14.

observed by Chan et al., (1983). In their tests, the maximum flame speed

decreased from 350 m/s with a closed top to about 5 m/s with a 50% open top. A

dramatic influence of top venting on flame acceleration was also observed by

van Wingerden and Zeeuwen (1985) in their tests with ethylene-air in a 4 m x 4 m

pipe-rack obstacle array. With complete top confinement they observed flame

acceleration to flame speeds of 420 m/s, whereas maximum flame speeds of only

24 m/s were reached with the top removed.

The effect of the venting of burned gases is to decrease the flame-induced

flow ahead of the flame. It is the interaction of the flame with the turbulent

flame-induced flow over the obstacles which is responsible for the increased rate

of burning. A positive feedback mechanism leading to flame acceleration is

established only if this increase in rate of burning produces a higher

flame-induced flow velocity ahead of the flame. In the present tests, except for

those with near stoichiometric acetylene-air, a balance between the flow ahead

and that vented out the top is established such that there is no continuous flame

acceleration.

In stoichiometric acetylene-air mixtures, the high rate of burning overcomes

the effect of top venting, the flame accelerates and reaches high enough

velocities to trigger localized explosions which lead to the onset of detonation.

It is important to note that the pressure waves observed prior to the localized

explosions are relatively weak U p < 2 bar) so that shock reflections alone

cannot account for the onset of detor.ation. In one test, ignition of the

turbulent end-pocket is sufficient to trigger onset of detonation. In this case,

the pressure is less than 140 mbar prior to the explosion in the end pocket.

Similar transistion to detonation, in a less sensitive mixture (5% C2H2-air), has

been reported by Moen et al., (1985). In their test, a fast flame emerging from

a tube produced violent burning and turbulence in a cloud contained in a plastic

bag, and a flame tongue triggered the explosion in a turbulent pocket.

Transitions to detonations in hydrogen-air clouds ignitied by a flame-jet

have also been observed (Schnildknecht, 1984; and Stock and Geiger, 1985), and

Pfortner et al., (1983) reported transition to detonation in a hydrogen-air cloud

UNCLASSIFIED

UNCLASSIFIED 15.

in which a fan was used to produce turbulence. Sherman et al., (1985) havereported transition to detonation in hydrogen-air mixtures contained in an almosttotally confined channel (13$ top venting).

All of the above observations of transition to detonation are associatedwith fast flame propagation. The presence of obstacles, confinement and otherperturbations enhances the probability of detonation. However, flame speeds muchlarger than the laminar flame speeds are required to produce the conditions fortransition to detonation. Such flame speeds can be produced by strong jetignition or by the acceleration of a flame ignited by a weak energy source. Withstrong jet ignition, transition to detonation in a lean acetylene-air mixturewhich is only slightly more sensitive than propane-air mixtures has been observed(Moen et al., 1985). Transition to detonation in even less sensitive fuel-airmixtures can therefore not be ruled out. In a chemical plant, fast flames andstrong ignition sources can be produced by explosions in confined channels suchas corridors, hallways and elevator shafts or in areas covered by a roof.

6. CONCLUSIONS

The results of a series of field tests on the propagation of flames in anopen-top channel with repeated obstacles have been reported. Tests wereperformed with acetylene, propane and hydrogen sulphide fuels mixed with air. Innear stoichiometric acetylene-air, the flame accelerates as it propagates downthe channel and reaches speeds up to 400 m/s prior to the occurrence of localizedexplosions which trigger the onset of detonation.

The behaviour of flames in lean acetylene-, propane- and hydrogensulphide-air mixtures is much less dramatic. The flame speeds observed rangefrom about 25 m/s up to 200 m/s, with associated pressures typically less than50 mbar. The continuous flame acceleration seen in more confined configurationsis not observed in the present configuration with these fuel-air mixtures.

UNCLASSIFIED

UNCLASSIFIED 16.

Based on these results i t can therefore be concluded the potential for flame

acceleration and t rans i t ion to detonation in the more open areas of a chemical

plant is much smaller than in the heavily confined areas. The fac t that flames

in stoichiometric acetylene-air do accelerate and produce detonations in these

obstacle environments shows that the potential for damaging explosions does

ex i s t . However, in order for such explosions to occur in the less sensit ive

propane-air or hydrogen sulphide-air mixtures, the cloud must be: i ) more

confined than in the present t es t s , i i ) igni ted by a stronger ign i t i on source

( i . e . , j e t i g n i t i o n ) , or i i i ) in an obstacle environment with more closely spaced

obstacles.

UNCLASSIFIED

UNCLASSIFIED 17.

7. REFERENCES

- Andrews, G.E. and Bradley, D. (1972a), "Determination of Burning Ve loc i t i es :

A C r i t i c a l Review", Combustion and Flame _18_, 133.

- Andrews, G.E. and Bradley, D. (1972b), "The Burning Velocity of Methane-Air

Mixtures" , Combustion and Flame _19_, pp. 275-288.

- Baker, W.E., Cox, P.A., Westine, P.S., Kulesz, J . J . and Strehlow, R.A.

(1983), "Explosion Hazards and Evaluat ion", Fundamental Studies in

Engineering Series, Volume 5, Elsevier Sc ien t i f i c Publishing Company,

Amsterdam, Holland.

- Brossard, J . , Desbordes, D., D i fab io , N., Gamier, J . L . , Lannoy, A . ,

Leyer, J .C . , Perrot , J . and Saint-Cloud, J.P. (1985), "Truly Unconfined

Deflagrat ions of Ethylene-Air Mixtures" , presented a t the 10th Internat ional

Colloquium on Dynamics of Explosions and Reactive Systems, Berkeley,

Ca l i f o rn i a , U.S.A., August.

- Chan, C , Moen, 1.0. and Lee, J.H.S. (1983), " Inf luence of Confinement on

Flame Accelerat ion Due to Repeated Obstacles", Combustion and Flame 49,

27-39.

- Funk, J.W., Murray, S.B. , Moen, 1.0. and Ward, S.A. (1982), "A Br ie f

Descr ipt ion of the DRES Fuel-Ai r Explosives Testing F a c i l i t y and Current

Research Program", in "Fuel-Air Explosions", edi ted by Lee, J.H.S. and

Guirao, CM. Proceedings of the In ternat iona l Conference on Fuel-Ai r

Explosions, held a t McGill Univers i ty , Montreal, Quebec, 4-6 November 1981,

SM Study No. 16, Univers i ty of Waterloo Press, Waterloo, Ontario,

pp. 565-583.

- Gibbs, G.J. and Calcote, H.F. (1959), "Ef fec t of Molecular Structure on

Burning Ve loc i t y " , Journal of Chemical Engineering Data 5^, 2226.

UNCLASSIFIED

UNCLASSIFIED 18,

Guirao, CM., Bach, G.G. and Lee, J.H. (1976), "Pressure Waves Generated bySpherical Flames", Combustion and Flame 27_, 341.

Hjertager, B.H. (1984), "Influence of Turbulence on Gas Explosions", Journalof Hazardous Materials j), pp. 315-346.

Kinder, J. (1979), "The Influence of Water Sprays on H2S-Air Flames",M.Eng. Thesis, McGill University, Montreal, Quebec.

Kuhl, A.L., Kamel, M.M. and Oppenheim, A.K. (1973), "Pressure WavesGenerated by Steady Flames", 14th Symposium (International) on Combustion,The Combustion Institute, Pa., pp. 1201-1215.

Lee, J.H., Guirao, CM., Chiu, K.W. and Bach, G.G. (1976), "Blast Effectsfrom Vapor Cloud Explosions", Loss Prevention (AIChE) _U.» PP« 59-70.

Lee, J.H.S. and Moen, 1.0. (1980), "The Mechanism of Transition fromDeflagration to Detonation in Vapor Cloud Explosions", Progress in Energyand Combustion Science j>, pp. 359-389.

Lind, C D . and Whitson, J. (1977), "Explosion Hazards Associated with Spillsof Large Quantities of Hazardous Materials", Phase III, report numberCG-D-85-77, United States Department of Transportation, U.S. Coast GuardFinal Report, ADA047585.

Moen, I.O., Donato, M., Knystautas, R., Lee, J.H. and Wagner, H. Gg. (1981),"Turbulent Flame Propagation and Acceleration in the Presence of Obstacles",Gasdynamics of Detonations and Explosions, edited by Bowen, J.R.,Manson, N., Oppenheim, A.K. and Soloukhin, R.I., Volume 75 of Progress inAstronautics and Aeronautics, pp. 33-47.

UNCLASSIFIED

UNCLASSIFIED 19.

Moen, 1.0. (1982), "The Influence of Turbulence on Flame Propagation i n

Obstacle Environments", i n "Fuel-Ai r Explosions", edi ted by Lee, J.H.S. and

Guirao, C M . , Proceedings of the Internat ional Conference on Fuel-Air

Explosions, held at McGill Un ivers i ty , Montreal, Quebec, 4-6 November 1981,

SM Study No. 16, Universi ty of Waterloo Press, Waterloo, Ontario,

pp. 101-134.

Moen, I .O. , Lee, J .H.S. , Hjertager, B.H., Fuhre, K. and Eckhoff, R.K.

(1982), "Pressure Development due to Turbulent Flame Propagation in

Large-Scale Methane-Air Explosions", Combustion and Flame 4]_, 31-52.

Moen, I .O. , Bjerketvedt, D., Jenssen, A. and Th ibaul t , P.A. (1985),

"Trans i t ion to Detonation i n a Large Fuel-Ai r Cloud", Combustion and Flame

6U pp. 285-291.

Moen, 1.0. and Saber, A . J . (1985), "Explosion Hazards of Hydrogen Sulphide

Phase I I . Flame Accelerat ion and Trans i t ion to Detonation Review", contract

repor t prepared fo r the Atomic Energy Control Board of Canada,

September 1985.

Pfor tner , H., Schneider, H., Drenckhahn, W. and Koch, C. (1983), "Flame

Accelerat ion and Pressure Build-Up in P a r t i a l l y Confined Clouds", presented

at the 9th Internat ional Colloquium on Dynamics of Explosions and Reactive

Systems, P o i t i e r s , France, Ju l y .

Schildknecht, M., Geiger, W. and Stock, M. (1984), "Flame Propagation and

Pressure Buildup i n a Free Gas-Air Mixture due to Jet I g n i t i o n " , Progress i n

Astronautics and Aeronautics 94_, pp. 474-490.

Schildknecht, M. (1984), "Versuche zur Freistrahlziindung von

Wasserstoff-Luft-Gemischen im Hinbl ick auf den Ubergang

Def lagrat ion-Detonat ion", Report BIeV-R-65.769-1, Ba t te l le I n s t i t u t e e.V. ,

F rank fu r t , West Germany.

UNCLASSIFIED

UNCLASSIFIED 20.

Schneider, H. and Pfôrtner, H. (1981), "Flammen und Druckwellenausbrutung

bei der Deflagration von Wasserstoff - Luft - Gemischen", Teil I , Ju l i

1978, Teli I I , Juni 1981, Fraunhoffer - Ins t i tu te fur Treib und

Explosivestoffe (ICT), Pfinztal-Berghaven, West Germany.

Schoite, T.G. and Vaags, P.B. (1959), "The Burning Velocity of Hydrogen-Air

Mixtures and Mixtures of some Hydrocarbons with A i r " , Combustion and Flame

_3, 495.

Sherman, M.P., Tiezsen, S.R., Benedick, W.B., Fisk, J.W. and Carcassi, M.

(1985), "The Effect of Transverse Venting on Flame Acceleration and

Transit ion to Detonation in a Large Channel", presented at the 10th

International Colloquium Dynamics of Explosions and Reactive Systems,

Berkeley, Cal i forn ia , U.S.A., August.

Stock, M. and Geiger, W. (1985), Battel le I ns t i t u t e.V., Frankfurt, West

Germany, pr ivate communication.

Strehlow, R.A., Luckr i tz, R.T., Adamczyk, A.A. and Shimpi, S.A. (1979), "The

Blast Wave generated by Spherical Flames", Combustion and Flame 35,

pp. 297-310.

Suimistras, A. , Moen, 1.0. and Saber, A.J . (1985), "Detonations in Hydrogen

Sulphide-Air Clouds", Suf f ie ld Memorandum Number 1140, Defence Research

Establishment Suff i e l d , Ralston, Alberta, February.

Urtiew, P.A. and Oppenheim, A.K. (1966), "Experimental Observations of

Transit ion to Detonation in an Explosive Gas", Proc. Royal Society A 295,

pp. 13-28.

UNCLASSIFIED

UNCLASSIFIED 21.

van Wingerden, C.J.M. and Zeeuwen, J.P. (1985), " Invest iga t ion o f

Explosion-Enhancing Propert ies of a Pipe-Rack-Like Obstacle Array",

presented at the 10th Internat ional Colloquium on Dynamics of Explosions and

Reactive Systems, Berkeley, Ca l i f o rn i a , U.S.A., August.

Zeeuwen, J.P. and van Wingerden, C.J.M. (1983), "On the Scaling of Vapour

Cloud Explosion Experiments", presented a t the 9th In ternat ional Colloquium

on Dynamics of Explosions and Reactive Systems, Po i t i e r s , France, Ju ly .

UNCLASSIFIED

TABLE I - Combustion Properties of Selected Stoichiometric Fuel/Air Mixtures

Initial Conditions: 1 atm. (1.013 bar), 25°C

Fuel

Hydrogen(H2)

Acetylene(C.H,)

Methane(CHH)

Ethylene(C2H4)

Propane(CjHB)

n-Butane

HydrogenSulphide

(H.S)

Mole %in Air

29.61

7.75

9.48

6.54

4.03

3.13

12.3

LaminarBurning

Velocity(m/s)

2.70a

1.44b

0.43c

0.68b

0.46b

0.39d

0.41e

Constant PressureDensity RatioAcross Flame

6.89

8.41

7.52

8.06

7.98

7.44

6.59

LaminarFlame Speed*

(m/s)

18.6

12.1

3.2

5.5

3.7

2.9

2.7

DetonationInitiationEnergy

(g tetryl)

1.1

1.25

22 x lO"1

(estimate)

10 NO GO15 GO

50 NO GO80 GO

50 NO GO80 GO

> 80

Cri t ica lTube

Diameter(m)

0.2

0.115

3.6+

0.43

0.9

0.7+

1.3+

DetonationVelocity(m/s)

1968

1864

1801

1822

1798

1796

1647

*Assumes velocity of burned gases is zero••"Estimate based on detonation cell sizea) Andrews and Bradley (1972a)b) Gibbs and Caicote (1959)

c) Andrews and Bradley (1972b)d) Scholte and Vaags (1959)e) Kinder (1979)

TABLE II - SUMMARY OF FLAME ACCELERATION

TESTNO.

13

14

10

12

9

11

20

FUEL%

$&

C3H8I%8

C H

4%8

C3Ha4hl%H2S913%

H,S12.9%

IGNITION

4

4

4

4

4

SPARKS

SPARKS

SPARKS

TUBE

SPARKS

TUBE

SPARKS

MAXIMUMFLAME SPEED

(m/s)

435+

180+

62

200

67

45

81

A.

AVERAGEFLAME SPEED

(m/s)

124+

85+

45

55

53

18

59

500 mm DIAMETER OBSTACLES

PEAKOVERPRESSURE

(mbar)

>155+

132+

86.2

7121

12.4

44.8

25.4

LAMINARFLAME SPEED*

(m/s)

12.1

11.0

3.7

3.7

3.7

1.5

2.6

COMMENTS

TRANSITION TO DETONATION AT THE END OFCHANNEL.

IGNITION DUE TO HOT WIRE AT END LEADS TOONSET OF DETONATION.

MAXIMUM PRESSURE AND VELOCITY NEARIGNITION END.

CENTRAL OBSTACLES ONLY

APPEARS TO SLOW DOWN.

18

19

15

16

17

C2H

C2H2

7.71%

C H4?0§%

C3H

H2S10.7%

4

4

4

SPARKS

SPARKS

TUBE

SPARKS

TUBE

97

375+

90

92

36

B.

51

86+

62

70

28.5

220 mm DIAMETER

51.7

303+

51.7

—

18.3

OBSTACLES

<7.4

12.1

3.7

3.7

2.1

TRANSITION TO DETONATION 10.7 M DOWNCHANNEL.

NO PRESSURE RECORDS.

+ Pre-detonation Values* Assumes velocity of burned gas is zero

0.01

UNCLASSIFIED SM 1159

SPHERICAL

GUIRAO ETAL. (1976)STREHLOW ETAL. (1979)

100 1000

MAXIMUM FLAME SPEED (m/s)

Figure 1

THEORETICAL CORRELATION OF MAXIMUM OVERPRESSURE VS MAXIMUMFLAME SPEED FOR CONSTANT VELOCITY FLAMES IN SPHERICAL

AND PLANAR GEOMETRIES

UNCLASSIFIED

IIIIIIIIIIIIII1IIII

czorGO

mD

TEST PAD

CAMERA-SHELTER

(30°) CAMERASHELTER

(90°)

INSTRUMENTATIONTRAILER

\FUEL FLOW

CONTROL TRAILER

Czo

T1ma

Figure 2

AERIAL VIEW OF TEST SITE

c2O

C/î

on

m

a) SIDE VIEW OF CHANNEL

c) OBSTACLES: END VIEW

i

b) END VIEW OF CHANNEL

d) OBSTACLES: SIDE VIEW

Figure 3

SELECTED PHOTOGRAPHS OF CHANNEL WITH 500 mm DIAMETER OBSTACLES

cznr

mc

czn

in

zïm

"77 7777 T'tTTT'Trr 7~TTT 7 I 77 / 77V T'TT" TTT77 ! 7 rT77T7 r r / 777 7 77 rtf TTTTTJ ! / / / ? /

CHANNEL SIZE: 1.8m x 1.8m IN CROSS SECTIONx 15.5 m LONG

• PRESSURE TRANSDUCERS: SPACING = 1.27m

T7 :

OBSTACLESDIAMETER = 500 mmSPACING(S) = 1.27 mHEIGHT(H) = 0.90 m

SUPPORT FRAME: DIAMETER = 60 mm

Figure 4

SIDE VIEW OF CHANNEL WITH 500 mm DIAMETER OBSTACLES m

cznr

en

2m

C2nr->on

a I OBSTACLES : END VIEW b ) OBSTACLES: SIDE VIEW

Figure 5

SELECTED PHOTOGRAPHS OF FLAME ACCELERATION CHANNEL WITH 220 mm OBSTACLESV)

czn

C/JC/5

ma

PLASTIC BAG

12

e -<u——O ( D - O €>

j rr

CHANNEL SIZE: 1.8 m x 1.8m IN CROSS SECTIONx 15.5 m LONG

PRESSURE TRANSDUCERS: SPACING = 1.27m

0 OBSTACLES

= SUPPORT FRAME: DIAMETER = 60 mm

DIAMETER = 220 mmSPACING(S) = 0.63 m

cz

m

Figure 6

SIDE VIEW OF FLAME ACCELERATION CHANNEL WITH 220 mm OBSTACLES


• ; 012 -

UJ

0.08

004-

000

TRIAL #13 7.80% C 2 H 2

500 mm OBSTACLES : SPARK IGNITION

I VELOCITYn PRESSURE

to 12

DISTANCE (ml

a ) MAXIMUM PRESSURE AND FLAME VELOCITY VS DISTANCE.

FROM PRESSURE RECORDS

9CDEG TEU- 90DEG WIDE

3UU.UU

400 00

300 00

20000

100 00

0 00-

i........90DEG WIDE

400 8.00 1200

DISTANCE (ml

16 00 20 00 0.00 400

TIME OF ARRIVAL VS DISTANCE

b) TIME OF ARRIVAL VS DISTANCE

FROM HIGH SPEED FILMS

8 00 12 00 16.01

DISTANCE [ml

VELOCITY VS DISTANCE

c) VELOCITY VS DISTANCE

FROM HIGH-SPEED FILMS

2000

Figure 7

FLAME PROPAGATION IN ACETYLENE-AIR 17.8% C 2H 2 )WITH 500 mm DIAMETER OBSTACLES AND SPARK IGNITION

UNCLASSIFIED


2000

1750

1500

1250 <

1000 •

750-

500

2K)

0

TRIAL #19 7.220mm OBSTACLES:

1 1 1 1 1 V

71% C 2 H 2

SPARK IGNITION

' VELOCITY 1

PRE SHOCK PRESS

11

1

"̂ ^-'| 1 , • • - . ,

4 6 8DISTANCE (ml

10 12

a) MAXIMUM PRESSURE AND FLAME VELOCITY VS DISTANCE.


0.20 !

0 16 '

0 08

0 04

000

/

J. ,

- - - 90 DEG TELE

1 1 1 1

000 400 800 1200

DISTANCE Iml

1600 20.00



2000

1600

_ 1200*E

400

0 0

90 DEG TEIE90 DEG WIDE

000 800 1200

DISTANCE (ml

1600

c ) VELOCITY VS DISTANCE


Figure 8

FLAME PROPAGATION AND TRANSITION TO DETONATION INACETYLENE-AIR (7.71% C 2H 2 ) WITH 220mm DIAMETER

OBSTACLES AND SPARK IGNITION

UNCLASSIFIED

UNCLASSIFIED S M 1159

a) 117.5 ms

V/7-7

c) 119.5 ms

b) 118.5 ms

à) 119.8 ms

e ) 120.1 ms f) 120.4 ms98T-/O

Figure 9

SELECTED FRAMES FROM THE 90° WIDE HIGH-SPEED FILM RECORDSHOWING FLAME ACCELERATION AND TRANSITION TO DETONATION

IN ACETYLENE-AIR (7.71% C 2 H 2 ) WITH 220 mm OBSTACLES ANDSPARK IGNITION

UNCLASSIFIED

znr->en

3.0 m

ui

<

V)

0C

a.

zo

oa.

4.3 m

5.5 m

6.8 m

[JOO m t o r ^

] 200 m bar

1 200 m bar

""ft\

4

k

illTil,

38 58 78 98 118 138

TIME (ms)

C

znrtoon

m

3 878 98 118 138

TIME (ms)

Figure 10

PRESSURE TIME HISTORIES AT VARIOUS POSITIONS DOWN THE CHANNEL FOR7.71% C 2 H 2 WITH 220mm DIAMETER OBSTACLES AND SPARK IGNITION


0 ms 25 ms 50 ms

75 ms 100 ms 125 ms

150 ms 175 ms 200 ms

Figure 11

IGNITION, FLAME ACCELERATION AND TRANSITION TO DETONATIONWITH ACETYLENE-AIR IN A 1.8m x 1.8m LANE. 15.5m LONG

UNCLASSIFIED


•ï 200

Z_ 175

| '50

S 125

S 10°- 75lu

1 "te

a0

TRIAL #14 7.5% C 2 H 2

500mm OBSTACLES: SPARK IGNITION, VELOCITY

PRESSURE

4 6

DISTANCE I m I

10 12



016-

0 08

004- 90 DEG TELE90DEG WIDE

000H000 400 800 1200

DISTANCE Im)


16 00 20 00

250 00

200 00-

150 00

u

u 10000>

50 00-

0 00

90 DEG TELE

90 DEG WIDE

400 8 00 12.00DISTANCE Iml

16 00 20.00

VELOCITY VS DISTANCE

b ) TIME OF ARRIVAL VS DISTANCE




Figure 12

FLAME PROPAGATION IN ACETYLENE-AIR (7.5% C 2H 2 )WITH 500 mm DIAMETER OBSTACLES AND SPARK IGNITION

UNCLASSIFIED


b) 169.2 ms

c) 170.2 ms d) 170.5 ms

e) 170.8 ms f) 171.1 ms

Figure 13

SELECTED FRAMES FROM THE 30° HIGH-SPEED FILM RECORD SHOWINGTHE EXPLOSION AND TRANSITION TO DETONATION IN THE TURBULENTEND-POCKET OF ACETYLENE-AIR PRIOR TO THE ARRIVAL OF THE MAIN

FLAME FRONT

UNCLASSIFIED


100

90

t 70O2 60> so

I «0E 30

£ 20

I 10

TRIAL #18 5.17% C 2 H 2

220 mm OBSTACLES: SPARK IGNITION' VELOCITY

" PRESSURE

4 6 8

DISTANCE (ml

10 12



i 030'2

000

I> 120 00

- 90OEG TELE

-90OEG WIDE

8 00 1200 1600 2000

DISTANCE 1ml

90DEG TELE

90DEG WIDE

800 1200

DISTANCE Iml

20 00

b ) TIME OF ARRIVAL FS DISTANCE


c I VELOCITY VS DISTANCE


Figure 14

FLAME PROPAGATION IN ACETYLENE-AIR (5.17% C2H2 )WITH 220 mm DIAMETER OBSTACLES AND SPARK IGNITION

UNCLASSIFIED


a ) 283 ms

b) 285ms

Figure 15

TWO FRAMES FROM THE 90° TELE HIGH-SPEED FILM RECORD SHOWINGTHE FLAME PROFILE TOWARDS THE END OF THE CHANNEL IN LEANACETYLENE-AIR (5.17% C 2H 2 ) WITH 220mm DIAMETER OBSTACLES

UNCLASSIFIED


TRIAL *10 4% C 3 H 8

500 mm OBSTACLES : SPAHK IGNITION

VELOCITY

PRESSURE

4 6DISTANCE (ml

10 12

a) MAXIMUM PRESSURE AND FLAME VELOCITY YS DISTANCE,


064

- 0 48

0.32

016

100 001

«0 00

- 60.00-

90OEG TELE

0 00 4 00 8.00 1200

0I5TANCE I m I



2000

800 1200

DISTANCE Iml

16 00



Figure 16

FLAME PROPAGATION IN PROPANE-AIR (4% C3H8> WITH500 mm DIAMETER OBSTACLES AND SPARK IGNITION

UNCLASSIFIED

czo

>on

mD

100-,

• « • 9 < H

oI—I

3'73•71

70

f>0

r>o-|

40

30

20

10

00

TRIAL # 9 4.14% C3HB500rnin OPSlACLfS: SPARK IGNITION

CENTRitL

-f- Veloi itya Pressure

. j . f..

I _ ___-—f-

B

~r- -i-

4 7

0

_, j —

8 10

Distanoe(m)ONLY

ooFigure 17

FLAME PROPAGATION IN PROPANE AIR (4.14% C 3 H 8 ) WITH 500 mm DIAMETER OBSTACLESIN THE CENTER ONLY AND SPARK IGNITION. MAXIMUM PRESSURE AND FLAME VELOCITY


czo

to

mD

J3

m

200

175

i r»o J

?T> H

0o

TRIAL #

I .

\

A \

2 n.1)5% C3HRC i r b : 7URE1 IGNITION

4-

-u-

eDisl.anoe(m)

•-|- Velocitya Pressure

... o-

10 f o

Figure 18

FLAME PROPAGATION IN PROPANE-AIR (3.95% C 3 H 8 ) WITH 500 mm DIAMETER OBSTACLESAND TUBE IGNITION. MAXIMUM PRESSURE AND FLAME VELOCITY FROM PRESSURE RECORDS

czn

m

C/3

2


000000 4 00 8 00 12 00 16 00

DISTANCE {ml


20 00

E 60 00

i> 40 00 -

ooo

«OOEG TELESO OEG WIDE

000 ' 0 0 SOD 12.00

OISTANCE (ml

VELOCITY VS OISTANCE

20 00

a) TIME OF ARRIVAL f.S DISTANCE

FROM HIGH SPEED FILMSb) VELOCITY >.S DISTANCE


Figure 19

FLAME PROPAGATION IN PROPANE-AIR (4.32% C 3H 8 ) WITH220 mm DIAMETER OBSTACLES AND SPARK IGNITION

(ZERO TIME CHOSEN AS TIME OF ARRIVAL OF FLAME AT 6.8m)

UNCLASSIFIED

cznr-

C/3

ma

•Il

•V

77!

Du

100-j

ÎM)-

Ï ÎO-

70 -

00-

:»0-

4 0 -

:«)-

L'O -

10 -

0 -

TRIAL § If) 1.05% (

y

1 1 1 1 1 1 1

•» ! HN 1 I

\

w

] Velocily

n l'rcssuri'

I | i

10 1 • >

Figure 20

FLAME PROPAGATION IN PROPANE AIR (4.05% C 3 H 8 ) WITH 220mm DIAMETER OBSTACLESAND TUBE IGNITION. MAXIMUM PRESSURE AND FLAME VELOCITY FROM PRESSURE RECORDS


3m

5.5 m

UJ

>UJa

O 6.8 m

O0.

8.1 m

9.3 m

100 m bar

425 '475 525 . 575

TIME (ms)

625 675

Figure 21

PRESSURE TIME HISTORIES AT VARIOUS POSITIONS DOWN THECHANNEL FOR 4.05% C 3 H 8 WITH 220 mm DIAMETER OBSTACLES

AND TUBE IGNITION

UNCLASSIFIED


a ) 24 ms

TWO FRAMES FROM THE 90° WIDE HIGH-SPEED FILM RECORD SHOWINGFLAME PROPAGATION IN A PROPANE-AIR MIXTURE WITH 220mm OBSTACLESAND SPARK IGNITION. (ZERO TIME CHOSEN AS TIME OF ARRIVAL AT 6.8m)

UNCLASSIFIED

czor>in

ma

. * * > '

oi—i

ai

73•71

100

90

ftO

70

00

50

10

20

10

00

TRIAL # 11 9.3% H2SiTirn OBSTACL.E.iv.Tube Ignition

A/ \

-V'' //

X4- \

•"I

4

-4-..4:

V......

+ Velocityn Pressurp

&-• B

"T"

0T

8Distance(m)

Figure 23

FLAME PROPAGATION IN HYDROGEN SULPHIDE-AIR (9.3% H2S) WITH 500mmDIAMETER OBSTACLES AND TUBE IGNITION.

MAXIMUM PRESSURE AND FLAME VELOCITY FROM PRESSURE RECORDS

<•£>

czn

mo

oi—i

ai

KM)

RI)>u -

70

KO

10-

LM)-

10-

00

TklALM ) i ) i n i i i f.J I ;'.KAI-1 I-:. ;NI f I' )N

V i ' L i K - i t y

< • > (îT r

Jl) 1 ïl

Figure 24 a

FLAME PROPAGATION IN HYDROGEN SULPHIDE-AIR (12.9% H2S> WITH 500 mmDIAMETER OBSTACLES AND SPARK IGNITION.

MAXIMUM PRESSURE AND FLAME VELOCITY FROM PRESSURE RECORDS


4.3 m

5.5 mLL

o

LUOC

COV)wec 6.9 m

CO

OQ.

9.3 m

10.6 m

25 m bar

25 m bar

25 m bar

25 m bar

100

\

200 300

TIME (msl

400 500

Figure 24 b

PRESSURE TIME HISTORIES AT VARIOUS POSITIONS DOWN THECHANNEL FOR 12.9% H2S WITH 500 mm DIAMETER OBSTACLES

AND SPARK IGNITION

UNCLASSIFIED

cznr

mD

o1—4

ai

*

s

0)

ai

100

90

80

70

r»o

r»o40

20

10

00

TRIAL # 17 10.7% H2S??Omm ORSTAOI ES: TUBP IGNITION

. - - • — I -

- ! • •

1 Velocityn Pressure

"t-

• r

4 106 8Dist.anee(m)

Figure 25 a

FLAME DEVELOPMENT IN HYDROGEN SULPHIDE-AIR (10.7% H2S) WITH 220mmDIAMETER OBSTACLES AND TUBE IGNITION.

MAXIMUM PRESSURE AND FLAME SPEED FROM PRESSURE RECORDS

n

t/3in

mc

co

\O


4.3 m

9.3 m

25 m bar

V

1400 1500 1600 1700 1800 1900

TIME I ms)

Figure 25 b

PRESSURE-TIME HISTORIES AT VARIOUS POSITIONS DOWN THECHANNEL FOR 10.7% H2S WITH 220 mm OBSTACLES AND TUBE IGNITION

UNCLASSIFIED

APPENDIX A

TABULATED PRESSURE RECORD RESULTS

Tarr = Time of arrival

Velocity = Flame Velocity

Pressure = Maximum pressure

PART I ACETYLENE-AIR

TRIAL NO. 13 AI-1

IGNITION: 4 SPARKS

CONCENTRATION: 7.80% C..H

OBSTACLES: 500 MM (CENTRAL and GROUND)

Channel

1O,IN11'

1

2

3

4

5

6

7

8

9

Distance(m)

TUBE

0.50

1.76

3.02

4.28

5.54

6.80

8.06

9.32

10.58

Tarr(ms)

88.7

50.7

- -

- -

- -

- -

102.9

110.9

115.9

Velocity(m/s)

- -

—

--

- -

—

--

120.7

157.5

252.0

Volts(mV)

680.0

33.0

200.0

428.0

450.0

2200.0

>2250.0

>1300.0

>2100.0

>2200.0

>2200.0

Cal(psi/V)

1.0

5.0

1.0

5.0

5.0

1.0

1.0

1.0

1.0

1.0

1.0

Pressure(mbar)

46.9

11.4

13.8

147.6

155.2

151.7

>155.2

>89.7

>144.8

>152.7

>151.7

TRIAL NO. 18 AI-4

IGNITION: 4 SPARKS

Channel

11.12J

1

2

3456

7

8910

Distance(m)

TUBE

0.501.763.024.285.546.808.069.32

10.5811.84

CONCENTRATION:OBSTACLES: 220

Tarr

(ms)

164.5304.8161.3180.0

193.3213.0

- -

248.6261.6278.1296.9

Velocity(m/s)

——

67.4

94.764.0- -

70.896.976.4

67.0

5.17% C/H/

MM

Volts(mV)

156.0

—

110.050.085.095.075.055.010.53.0

3.0

6.3

Cal

(ps1/V)

1.0

5.0

1.0

5.0

5.0

5.0

10.010.050.0

100.0100.050.0

Pressure(mbar)

10.8—

7.6

17.229.332.851.737.936.220.7

20.721.7

PART I I PROPANE-AIR

TRIAL NO. 9 AI 1-2

Channel

1

2

3

4

5

6

7

8

9

10

Distance

(m)

0.50

1.76

3.02

4.28

5.54

6.80

8.06

9.32

10.58

11.84

IGNITION:

CONCENTRATION

OBSTACLES: 500

Tarr

(ras)

177.0

195.9

—

234.8

—

—

318.8

344.5

Veloci ty

(m/s)

—

66.7

- -

64.8

- -

—

45.0

49.0

4 SPARKS

: 4.14* C,f

MM (CENTRAL

Volts

(mV)

6.0

13.0

14.5

18.0

17.0

15.0

9.0

8.0

8.5

ONLY)

Cal

(psi/V)

10.0

10.0

10.0

10.0

10.0

10.0

10.0

10.0

10.0

10.0

Pressure

(mbar)

4.1

9.0

10.0

12.4

11.7

10.3

6.2

5.5

5.9

TRIAL NO. 15 AII-4

IGNITION: TUBE

CONCENTRATION: 4.05% C3H£

OBSTACLES: 220 MM

Channel

10}IN11

1

2

3

4

56789

Distance(m)

TUBE

0.501.76

3.024.28

5.546.80

8.069.32

10.58

Tarr(ins)

385.3478.4503.1

—

- -

576.3593.8

607.8625.0

Velocity(m/s)

—--

51.0—

—

51.672.0

90.073.3

Volts<mV)

—- -

- -

150.0- -

530.0530.0

416.0450.0

Cal(psi/V)

LO

5.0

KO

5.0

5.0

1.0

1.0

1.0

1.0

1.0

1.0

Pressure(mbar)

. .

- -- -

—

51.7—

36.636.628.7

31.0

PART III HYDROGEN SULPHIDE/AIR

Channel

12

1

2

3

4

5

6

7

8

9

10

Distance(m)

TUBE

0.501.76

3.024.28

5.546.80

8.06

9.32

10.5811.84

TRIAL

IGNITION

CONCENTRATION:

OBSTACLES: 220

Tarr

(ms)

1132.0

1512.0

1570.0

1620.0

1658.0

1693.0

- -

- -

1823.0

1861.0

1923.0

1973.0

Velocity

(m/s)

. .

----

25.2

33.2

36.0

—

--

29.1

33.2

20.3

25.2

NO. 17

: TUBE

10.7% H2S

MM

Volts

(mV)

. .

28.0

—

—

36.0

260.0

260.0

250.0

225.0

175.0

350.0

Cal

(psi/Y)

1.0

5.0

1.0

5.0

5.0

1.0

1.0

1.0

1.0

1.0

1.0

5.0

All 1-3

Pressure(mbar)

9.7

—

—

12.418.317.917.215.5

12.1

24.1

TRIAL NO. 20 AIII-2

IGNITION: 4 SPARKSCONCENTRATION: 12.9% H2SOBSTACLES: 500 MM (CENTRAL & GROUND)

Channel Distance(m)

Tarr(tns)

Velocity(m/s)

Volts(nV)

Cal(psi/V)

Pressure(mbar)

12

1

2

3

4

5

6

7

8

9

10

N TUBE

0.50

1.76

3.02

4.28

5.54

6.90

8.06

9.32

10.58

11.84

210.3

—

260.0

285.3

309.7

- -

345.0

360.6

380.6

410.0

- -

—

—

49.8

51.6

—

71.4

80.863.0

42.9

1000.0

300.0304.0

—

61.0368.0

295.0216.0150.0155.0

150.0

1.0

5.0

1.0

5.0

5.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

69.0

103.421.0- -

21.025.4

20.314.910.310.7

10.3

ANNEX C

TURBULENT FLAME PROPAGATION AND TRANSITIONTO DETONATION IN LARGE FUEL-AIR CLOUDS

by

I.O. Moen, A. Sulmistras,B.H. Hjertager and J.R. Bakke

TURBULENT FLAME PROPAGATION AND TRANSITION TO DETONATIONIN LARGE FUEL-AIR CLOUDS*

I.O. MoenDefence Research Establishment Suffield

Ralston, Alberta, Canada TOJ 2N0

A. SulmistrasDepartment of Mechanical Engineering

Concordia University,Montreal, Quebec, Canada

B.H. Hjertager and J.R. BakkeThe Chr. Michel sen Institute

Department of Science and TechnologyBergen, Norway

* Proceedings 21st International Symposium on Combustion, Munich, West Germany,August 3-8, 1986

ABSTRACT

The results of a series of flame acceleration tests performed in atop-vented channel, 1.8 m x 1.8 m in cross-section and 15.5 m long, with repeatedobstacles are reported. The tests were performed in order to assess thepotential for flame acceleration and transition to detonation following anaccidental spill of gaseous fuel in simulated industrial environments withrepeated obstacles. Tests were performed with acetylene, propane and hydrogensulphide fuels mixed with air. For near stoichiometric acetylene-air, the flameaccelerates continuously as it propagates down the channel reaching speedsbetween 180 and 400 m/s prior to the occurrence of localized explosions whichtrigger the onset of detonation. The behavior of flames in lean acetylene (5.2%C,H 2)-, propane- and hydrogen sulphide-air mixtures is much less dramatic. Theobserved flame speeds range from about 25 m/s up to 200 m/s, with associated peakoverpressures typically less than 50 mbar. The continuous flame accelerationobserved in stoichiometric acetylene-air is not observed in these mixtures.Based on these results it is concluded that the potential for flame accelerationand transition to detonation in the more open areas of a chemical plant is muchsmaller than in the heavily confined areas. The fact that flames instoichiometric acetylene-air accelerate and produce detonations in these obstacleenvironments shows that the potential for damaging explosions does exist.However, higher levels of confinement, stronger ignition sources or denserobstacle configurations than in the present tests are required to produce suchexplosions in less sensitive mixtures. The results of numerical simulations ofthe turbulent flame propagation are also reported and compared with the observedresults. These simulations successfully describe many of the observed phenomena.In particular, the flame acceleration in acetylene-air mixtures and the absenceof similar flame acceleration in propane- and hydrogen sulphide-air mixtures arepredicted.

1. INTRODUCTION

Explosions resulting from the accidental spills of a variety of gaseousfuels continue to occur with increasing frequency, sometimes with devastatingconsequences. It has therefore become necessary to realistically assess thepotential explosion hazards associated with accidental spills in chemical andindustrial plant environments. Such spills typically occur within the plantitself, in a complex obstacle configuration involving arrays of pipes, conduitsand pipe racks, as well as buildings and other confining structures. It is thepresence of these obstacles and confining spaces which is thought to beresponsible for producing violent combustion and potentially damaging blastwaves.

The most severe type of fuel-air explosion is a detonation, which propagatesthrough the detonable parts of the fuel-air cloud producing pressures in excessof 15 bar. In view of the large energies required to directly initiatedetonation in fuel-air mixtures, this worst case scenario is typically excludedin hazard assessments. However, recent experimental tests have shown thattransition to detonation can occur under certain circumstances, even forrelatively insensitive fuel-air mixtures.1-3 Furthermore, acceleration of flamesto speeds which produce damaging blast waves has been observed in both accidentsand experimental tests. It is therefore important to determine the conditionsthat lead to violent explosions so that appropriate measures can be taken toeliminate these conditions.

A wide variety of experimental tests, both large and small scale, have beenperformed so that there is now a considerable data base available on fuel-airexplosions and the blast waves produced by such explosions. Based on theseresults, particularly hazardous obstacle configurations can be identified asthose which are heavily confined. In tubes, pipes and channels, for example,high flame speeds and potentially damaging pressures are reached within less thanfour diameters, even for insensitive mixtures of methane and air.*1 Similar flameacceleration is also observed in clouds which are confined between twosurfaces.5"7 On the other hand, weak spark ignition of an unconfined cloud in arelatively unobstructed environment is unlikely to result in a damagingexplosion, even for relatively sensitive fuels such as hydrogen andacetylene.8"10

- 2 -

In par t ia l ly confined regions with obstacles, which are more typical of

chemical plants, the acceleration of flames is less dramatic than in heavily

confined regions and depends c r i t i ca l l y on the size of the cloud, the degree of

confinement, the obstacle configuration, the ignit ion source and the fuel -a i r

mixture. The influence of top venting on methane-air flame acceleration in a

laboratory scale channel with obstacles was investigated by Chan et a l . 1 1 In

their tests, the maximum flame speed decreased from 350 m/s with a closed top to

about 5 m/s with a 50% open top. A similar influence of top venting on flame

acceleration was also observed by van Wingerden and Zeeuwen6 in their tests in a

4 m x 4 m pipe-rack obstacle array. Although qualitative descriptions of the

influence of various factors on the flame acceleration phenomena are well<• 5 6 1 1

established, ' * ' quantitative methods capable of modelling the complexcoupled chemical and fluid-dynamic processes involved are scarce. A numericalmethod which treats the coupling between flow, turbulence, heat release, mixingand pressure rise by use of submodels for each of the individual processesinvolved has been proposed by Hjertager. ' This model has been used tosimulate methane-air and propane-air explosions in tube geometries withobstacles13 and methane-air explosions in top-vented obstructed channels. ' Ofparticular importance are the scaling predictions for explosions in ventedchannels, which show that the pressure developed in partially confined obstacleconfigurations increases with the size of the cloud. With 50% top venting, forexample, the overpressure predicted for the laboratory scale channel ofChan et al.11 is very small (~10"2 bar), as observed. However, pressures inexcess of 1 bar are predicted in a similar channel scaled up linearly by a factorof 20. Since fuel-air clouds of this size and larger can easily be produced inan accidental spill, it is important to perform tests on a large scale in orderto assess the potential for hazardous explosions and to further validatenumerical predictions.

The present paper reports on an experimental and numerical investigation offlame propagation in a partially confined channel, 1.8 m x 1.8 m in cross-sectionand 15.5 m long, with repeated obstacles. The aim of this study is to assess thepotential for flame acceleration in configurations which simulate a chemicalplant environment with arrays of pipes in the fuel-air cloud. Tests wereperformed with repeated cylindrical obstacles of two diameters {500 and 220 mm)for fuel-air mixtures based on acetylene, propane and hydrogen sulphide fuels.

- 3 -

As seen in Table I, these fuels cover a wide range of laminar flame speeds anddetonation sensitivity. Experimental results obtained at stoichiometriccomposition for each fuel are compared with numerical predictions, and numericalpredictions for even larger clouds are presented.

2. EXPERIMENTAL DETAILS

2.1 Experimental Configuration and Procedure

The test section consisted of a channel, 1.8 m x 1.8 m in cross-sectionand 15.5 m long, constructed on a support frame of 60 mm diameter aluminumtubing. The sides of the channel were confined by plywood or plexiglass sheets,which were hinged in such a manner that they would swing out prior to beingdestroyed by the explosion. The bottom was confined by the test pad. The onlytop confinement was due to the plastic envelope which enclosed the channel andjoined it at one end to a 0.9 m diameter tube, 7.6 m long. Two obstacleconfigurations were tested, corresponding to 500 mm and 220 mm diameter tubesmounted across the channel at regular intervals as illustrated in Figures 1and 2.

Tests in each obstacle configuration were performed with acetylene(C 2H 2), propane (C3H8) and hydrogen sulphide (H2S) fuels. The test gases weremixed with the initial air in the test volume by a multipath recirculationsystem, and the composition and mixture homogeneity were monitored using anIR-gas analyzer. Ignition of the flame was achieved by four sparks mountedacross the channel at the tube end. This form of ignition was used to simulateline ignition which would produce approximate two-dimensional flame propagationand flow down the channel. The total energy (*s CV2) supplied to the four sparkswas 8.4 Joules. In selected tests, the plastic confinement at the far end of thechannel was removed just prior to ignition using a hot wire to cut the plasticenvelope. Selected tests were also performed with spark ignition at the far endof the tube.

- 4 -

2.2 Diagnostic Systems and Data Analyses

The arrival and pressure prof i le of the wave were monitored at up to

ten positions along the bottom of the channel by piezoelectric pressure

transducers, as i l lust rated in Figures 1 and 2. The time-of-arrival of the flame

is assumed to coincide with the peak in pressure, typical ly observed just prior

to the decay into a negative pressure phase which indicates that the main flame

front has passed. The time-of-arrival obtained in this manner is in good

agreement with that obtained from the high-speed f i lm records.

Three high-speed cameras (~3000 frames/sec) were used to record the

flame propagation. Two cameras were placed 90° to the channel axis, and the

th i rd camera was placed at a 30° angle to the channel axis. The records from the

two 90° cameras were analysed by monitoring the time-of-arrival of the leading

flame front vs posit ion, and the flame velocity was deduced from this data.

Although the flame zone was observed to be wrinkled, folded and relat ively th ick,

the flame was observed to propagate as a thick turbulent flame brush extending

from the bottom to the top of the channel. Except for local variations in the

velocity of the front as i t propagates around obstacles, the flame velocity

reported corresponds to the velocity of this flame brush.

The venting out the top as the plastic was torn and the motion of the

plywood and plexiglass side confinement were also observed on the high-speed

f i lms. In a l l tests, the tearing of the plastic coincides approximately with the

arr ival of the flame and the sides either remained intact or blew-out long after

the flame had passed. Complete side confinement with top venting of the burned

gases can therefore be assumed in a l l tests.

3. NUMERICAL SIMULATION

7 12

The numerical model has been described in detail elsewhere, ' so that onlya brief description will be given here. The governing equations for mass,momentum and energy, together with equations describing the combustion, aresolved by specifying the relevant fluxes and combustion rates, and theappropriate boundary conditions. Combustion is treated as a single-step

- 5 -

irreversible reaction with finite reaction rate between fuel and oxidizer. Thefluxes of momentum, energy and fuel are expressed in terms of time-mean gradientsof the relevant variables by introducing effective turbulent transportcoefficients in the standard manner. These transport coefficients are determinedby the so called k-e model of turbulence as described in detail in References 7and 12.

The combustion rate R* is assumed to be proportional to the rate ofdissipation of kinetic energy e and the limiting mass fraction m,. of fuel,oxidizer or reaction products as follows:

where p is the density, k is the kinetic energy of turbulence and A is aconstant. This expression assumes fast chemistry. In order to take into accountthe effects of finite chemical rates, a criterion based on the ratio of thechemical induction time T to the eddy lifetime or mixing time T ~ k/e is used.Ignition or extinction is assumed to occur when these two times are in a givenratio. The reaction rate in Equation 1 applies only when the ratio of T/T issmaller than this given ratio, otherwise the reaction rate is equal to zero. Thechemical induction time correlations used for the present calculations are givenin Table I.

With the above formulations for turbulence and combustion, the conservationequations can be written in the following general form:

3 3 3 8 *— ( P * ) + (PU.*) = (: ) + S . (2)at 3x. J ax. ax,.

Solution of these equations is performed by finite-domain methods as described in

detail in Reference 12.

- 6 -

Calculations of flame and pressure development were performed for the three

fuels (C2H2, C3H8 and H2S) mixed with air at stoichiometric composition in a

vented channel of the same dimensions as that used in the experiments. The

channel was assumed to be confined on three sides and at the ignitïon end, while

the top and far end were open. In order to make the calculations tractable,

obstacles with a square cross-section (500 x 500 mm2) were placed in the channel

in a configuration which simulates the experimental configuration as closely as

possible within the current resolution l imi tat ions. Typical results showing the

distr ibut ion of velocity, combustion rate and fuel fraction for acetylene-air ar-d

propane-air explosions are also included in Figure 3. The venting of burned

gases out the top and the relat ively high combustion rate in the turbulent region

between the obstacles can be seen in this f igure. Although the flame zone is

relat ively th ick, with flame je t t ing around the obstacles and after-burning near

the bottom of the channel, the flame appears to propagate as a thick turbulent

flame-brush, extending from the bottom to the top of the channel, in agreement

with experimental observations. In spite of the large difference in the

magnitude of the predicted veloci t ies, the flame and velocity prof i les are very

similar in the two mixtures. Comparisons of predicted and observed flame

velocit ies and pressures for the dif ferent fuel -a i r mixtures wi l l be made in the

next section.

4. RESULTS AND DISCUSSION

The potential for flame acceleration and transition to detonation is clearlyillustrated by the results obtained in near stoichiometric acetylene-airmixtures. For these mixtures, the flame accelerates down the channel and reachesspeeds between 250 -̂«d 400 m/s prior to the occurrence of localized explosionswhich trigger the onset " detonation. The flame velocity and peak overpressureobserved as the flame propagates down the channel are shown in Figure 4. Forboth the small and the large obstacles, the flame propagates in a sporadic mannerdown the first half of the channel. The general trend is acceleration of theflame. With the larger (500 mm) obstacles, the leading flame front reaches theend of the channel with a velocity of about 400 m/s, at which time a localizedexplosion near the bottom of the channel triggers detonation of the remaining

- 7 -

unburned mixture. The peak pressure reaches about 150 mbar at 2 m. Similarpressures are recorded out to 4 m; beyond that the records are off-scale,indicating pressures larger than 150 mbar.

The results from the numerical calculations are also shown in Figure 4.Since there is no criterion or mechanism for transition to detonation built intothe code, this phenomena is not obtained. However, the flame is predicted toaccelerate. In fact, the predicted maximum flame speed of 650 m/s is higher thanthat observed experimentally prior to the onset of the detonation. The predictedpeak pressure, which occurs at the end of the channel, is 3.6 bar. As expected,these values depend on the prescribed initial flame velocity. The results shownin Figure 4 are for an initial flame velocity of 11.0 m/s. Better agreement withthe observed pre-detonation behavior is obtained with an initial velocity of5 m/s.

With the smaller 220 mm obstacles, transition to detonation occurs about11 m down the channel, again due to a localized explosion at ground level. Theflame speed reaches about 250 m/s prior to a rapid acceleration phase whichstarts 9 m down the channel and results in a full-fledged detonation with avelocity close to the theoretical value by the end of the channel (seeFigure 4a). Prior to the rapid acceleration phase, the peak pressure is lessthan 2 bar. The peak pressure quickly increases to a detonation-like pressure ofabout 15 bar at 10.6 m (see Figure 4b). Selected frames from a high-speed filmrecord showing the flame propagation and transition to detonation are included inFigure 5. The first two frames (Frames a and b) show the flame during the rapidacceleration phase. Notice that there are several bright spots within the flamebrush, indicating that localized explosions are occuring. The explosion near theflame front at ground level in Frame c grows, as seen in the next two frames(Frames d and e), and finally results in the detonation wave seen in Frame f.

The two tests described above illustrate the classic mechanism of flameacceleration in an obstacle environment, with explosions somewhere in theaccelerating turbulent flame brush triggering the onset of detonation. Themechanism of transition to detonation is >/ery similar to that observed by Urtiewand Oppenheim,18 but on a much larger scale with a less sensitive mixture.Another mode of transition to detonation was observed in a test with 7.5Ï C2H2.

- 8 -

In this test, ignition of the turbulent pocket at the end of the channel, by thehot wire used to cut the plastic, produces transition to detonation prior to thearrival of the main flame front. The phenomena involved are illustrated by thesequence of frames from a high-speed film record shown in Figure 6. Theturbulent burning in the end-pocket, which is shown in the first two frames(Frames a and b), results in an explosion near ground level, as seen in Frames cand d. The subsequent detonation of the remaining unburned mixture prior to thearrival of the main flame front can be seen in the last two frames.

The maximum velocity of the main flame front, prior to the onset ofdetonation, is 180 m/s with an associated peak overpressure of 132 mbar. Suchr assures are much too small for shock reflections to be responsible for theonset of detonation. However, the flame-induced flow produces a pocket ofturbulent flow at the end of the channel. As seen in Figure 6, it is theignition of this pocket which triggers an explosion of a sufficiently largevolume to cause transition to detonation. Similar transition to detonation, in aless sensitive mixture 15% C2H2-air), was observed in a previous test by Moen etal.2 In that test, a fast flame emerging from a tube produced violent turbulentburning in a cloud contained in a plastic bag and a flame tongue triggered theexplosion in a turbulent pocket.

The three tests described above were performed with near stoichiometricacetylene-air mixtures. The laminar flame speed in these mixtures is relativelyhigh and the mixtures are also relatively sensitive to detonation, with acritical tube diameter of about 0.12 m (see Table I). In the presentconfiguration, the propagation of flames in less sensitive mixtures is much lessdramatic. With lean 5.2% C2H2-air, for example, the flame propagates down thechannel with a velocity between 60 and 100 m/s producing overpressures less than55 mbar. Similar flame behavior is also observed in propane-air mixtures.

The flame velocities and peak pressures observed with near stoichiometricpropane-air are given in Figure 7. With the 500 mm obstacles, a maximum flamespeed of 62 m/s is observed about half-way down the channel. By the end of thechannel, the flame has slowed down to 30 m/s (see Figure 7a). The peak pressureof 86 mbar is observed at 1.76 m prior to the tearing of the plastic envelope.Once the envelope is torn, allowing top venting of the burned gases, the peak

- 9 -

pressure remains below 30 mbar (see Figure 7b). As seen in Figure 7, the

behavior of the flame predicted by the numerical model is in excellent agreement

with that observed. Since confinement effects due to the plastic envelope are

not included in the model, the higher pressure observed prior to the tearing of

this envelope is not accounted for . However, once venting of the burned gases

occurs the predicted and observed pressures agree (see Figure 7b). The numerical

results shown in Figure 7 are for an i n i t i a l flame velocity of 9.5 m/s. Although

the numerical results depend on the choice of i n i t i a l velocity, the key

prediction is that the flame does not continuously accelerate producing higher

and higher pressure even with i n i t i a l flame speeds 2.5 times the laminar flame

speed. This should be contrasted with the results for acetylene-air where

continuous flame acceleration is predicted with an i n i t i a l speed of 5 m/s, which

is less than half the laminar flame speed for this mixture (see Table I ) .

The flame velocity observed in C3H8/air with the smaller 220 mm obstacles is

also shown in Figure 7a. Although the velocity is somewhat higher than that

observed with the larger obstacles, there is again no evfdence of continuous

flame acceleration. Tests were also performed with ignit ion at the end of the

tube. In these tests, the propane-air mixture in the channel is ignited by a

flame-jet from the tube. Although there were no obstacles in the tube to

accelerate the flame, the maximum i n i t i a l flame velocity obtained in this manner

was 200 m/s. Even with this i n i t i a l velocity, the flame in the channel rapidly

slows down to speeds similar to those observed with spark ign i t ion . The peak

pressures are also similar to those observed with spark ign i t ion . A summary of

a l l the tests results is given in Table I I .

In H2S-air mixtures, the flame is not visible so that no high-speed f i lm

analysis was possible and the flame propagation is obtained solely from the

pressure records. As seen in Figure 8, the behavior of the flame in these

mixtures is very similar to that in propane-air with maximum velocities less than

80 m/s and peak pressures less than 30 mbar. No continuous flame acceleration or

build-up of pressure is predicted or observed in any of the tests with H2S-air.

The predicted flame velocity, with an i n i t i a l flame speed of 8.5 m/s, is less

than that observed in the 500 mm obstacle configuration (see Figure 8a). The

pressures are also'underestimated (see Figure 8b).

- 10 -

The fact that the predictions of the numerical model do not agree in detailwith the experimental observations is not suprising since there are many aspectsof the experimental configuration which are not included in the numerical code.These include: the shape of the obstacles, the plastic envelope, the supportframe, the tube which is connected to the channel, ignition with four sparksrather than line ignition, and side venting. Furthermore, the numerical modelincorporates turbulent combustion through a simplified mixing model limited by asingle-step induction time. In spite of these shortcomings, the model accountsfor many of the phenomena observed. Transition to detonation cannot be describedby the model in its present form. However, the continuous flame accelerationobserved in stoichiometric acetylene-air mixtures prior to detonation ispredicted. The model also correctly predicts that flames in propane- andhydrogen sulphide-air will not continuously accelerate in the presentconfiguration. The predicted **4 maximum flame velocities and overpressures forthese mixtures also agree quite well with those observed.

In propane-air mixtures, the observed and predicted maximum flame speeds are15-25 times the laminar flame speed, and the overpressure is typically less than50 mbar. Comparison of these results with the flame speeds up to 620 m/s andpeak overpressures up to 14 bar observed in a confined tube on a similar scale(2.5 m diameter tube, 10 m long)7, clearly shows the dramatic influence ofconfinement on the development of fuel-air explosions in obstacle environments.This influence is correctly predicted by the numerical model.

The flame speeds observed in propane-air mixtures are up to four timeslarger than the maximum flame speed observed in the same mixtures in a similarlaboratory scale channel with obstacles19. However, there is no evidence toindicate that the continuous flame acceleration observed in more confinedconfigurations will occur for this mixture with this level of confinement. Asseen in Figure 9, the peak explosion pressure is predicted to increase withscale, but even in a channel scaled up linearly by a factor of 8 from the presentconfiguration, the peak pressure is predicted to be less than 150 mbar. Asimilar increase in peak pressure with scale is also predicted in hydrogensulphide-air mixtures, and the predictions for acetylene-air indicate thattransitition to detonation is also expected in larger clouds.

- 11 -

5. CONCLUSIONS

The results of a series of field tests on the propagation of flames in anopen-top channel wîth repeated obstacles have been reported. Tests wereperformed with acetylene, propane and hydrogen sulphide fuels mixed with air. Innear stoichiometric acetylene-air, the flame accelerates as it propagates downthe channel and reaches speeds up to 400 m/s prior to the occurrence of localizedexplosions which trigger the onset of detonation. The behavior of flames in leanacetylene-, propane- and hydrogen sulphide-air mixtures is much less dramatic.The flame speeds observed range from about 25 m/s up to 200 m/s, with associatedpressures typically less than 50 mbar. The continuous flame acceleration seen inmore confined configurations is not observed in the present configuration withthese fuel-air mixtures.

Based on these results it can therefore be concluded the potential for flameacceleration and transition to detonation in the more open areas of a chemicalplant is much smaller than in the heavily confined areas. The fact that flamesin stoichiometric acetylene-air accelerate and produce detonations in theseobstacle environments shows that the potential for damaging explosions doesexist. However, in order for such explosions to occur in the less sensitivepropane-air or hydrogen sulphide-air mixtures, the cloud must be: i) moreconfined than in the present tests, ii) ignited by a stronger ignition source{i.e., strong jet ignition from a confined explosion), or iii) in an obstacleenvironment with more closely spaced obstacles.

Numerical simulations of the flame propagation using a k-e turbulence model,which incorporates turbulent combustion through a mixing model limited by asingle-step induction time, describe many of the observed phenomena. Inparticular, the flame acceleration in acetylene-air mixtures and the absence ofsimilar flame acceleration in propane- and hydrogen sulphide-air mixtures arepredicted.

Future numerical and experimental research to determine the criticalconfinement, ignition and obstacle conditions for continuous acceleration andtransition to detonation in the less sensitive fuel-air mixtures are recommended.Such critieria would allow appropriate measures to be taken to eliminate theseconditions within chemical and industrial plants.

- 12 -

ACKNOWLEDGEMENTS

The experimental part of the investigation described in this report wassponsored and funded by the Atomic Energy Control Board of Canada. The numericalwork has been financially supported by BP Petroleum Development Ltd., Norway, ElfAquitaine Norge A/S, Esso Exploration and Production Norway Inc., MobilExploration Norway Inc., Norsk Hydro and Statoil, Norway.

The valuable assistance of Gayle Hall and Chris Brosinsky in planning andcarrying out the field trials is gratefully acknowledged. We would also like tothank the personnel of the Field Operations Section, the Electronic Design andInstrumentation Group, and the Photo Group at DRES for their assistance duringthe field trials.

- 13 -

REFERENCES

1. Pfortner, H., Schneider, H., Drenckhahn and Koch, C : "Flame Accelerationand Pressure Build-Up in Free and Partially Confined Clouds", presented atthe 9th International Colloquium on Dynamics of Explosions and ReactiveSystems, Poitiers, France, July 1983.

2. Moen, I.O., Bjerketvedt, D., Jenssen, A. and Thibault, P.A.: Combustion andFlame 6^, 285 (1985).

3. Sherman, M.P., Tieszen, S.R., Benedick, W.B., Fisk, J.W. and Carcassi, M.:"The Effect of Transverse Venting on Flame Acceleration and Transition toDetonation in a Large Channel", presented at the 10th InternationalColloquium on Dynamics of Explosions and Reactive Systems, Berkeley,California, U.S.A., August 1985.

4. Moen, I.O., Lee, J.H.S., Hjertager, B.H., Fuhre, K. and Eckhoff, R.K.:Combustion and Flame 47_, 31 (1982).

5. Moen, I.O., Donato, M., Knystautas, R., Lee, J.H. and Wagner, H.Gg.:Prog. Astronautics and Aeronautics jf5_, 33 (1981).

6. van Wingerden, C.J.M. and Zeeuwen, J.P.: "Investigation of Explosion -Enhancing Properties of a Pipe-Rack Like Obstacle Array", presented at the10th International Colloquium on Dynamics of Explosions and ReactiveSystems, Berkerley, California. U.S.A., August 1985.

7. Hjertager, B.H.: J. Hazardous Materials £, 315 (1984).

8. Lind, C D . and Whitson, J.: "Explosion Hazards Associated with Spills ofLarge Quantities of Hazardous Materials", Phase III, U.S. Department ofTransportation, U.S. Coast Guard Report No. CG-D-85-77, (1977).

- 14 -

REFERENCES (cont'd)

9. Schneider, H. and Pfôrtner, H.: "Flammen- und Druckweilenausbreitung bei

der Deflagration von Wasserstoff-Luft-Gemischen", Teil I , Juif 1978, Teil

I I , Juni 1981, Fraunhofer-Institut fur Trieb- und Explosivstoffe (ICT),

Pfinztal-Berghausen, West Germany.

10. Brossard, J . , Desbordes, D., Difabio, N., Gamier, J.L.» Lannoy, A.,

Leyer, J.C., Perrot, J . and Saint-Cloud, J.P.: "Truly Unconfined

Deflagrations of Ethylene-Air Mixtures", presented at the 10th International

Colloquium on Dynamics of Explosions and Reactive Systems, Berkeley,

Cali fornia, U.S.A., August 1985.

11. Chan, C , Moen, 1.0. and Lee, J.H.S.: Combustion and Flame 49, 27 (1983).

12. Hjertager, B.H.: Combustion Science Technology 2_7_. 159 (1982).

13. Hjertager, B.H., Fuhre, K., Parker, S.O. and Bakke, J.R.: Prog.

Astronautics and Aeronautics 94_, 504 (1984).

14. Bakke, J.R. and Hjertager, B.H.: "Numerical Simulation of Methane-Air

Explosions in Vented, Obstructed Channels: Scaling Characteristics", Report

CMI No 823403-5, Chr. Michel sen Inst i tu te , Bergen, 1983.

15. Kistiakowsky, G.B. and Richards, L.W.: J. Chem. Phys. 36, 1707 (1962).

16. Burcat, A., L i fsh i tz , A., Scheller, K. and Skinner, G.B.: Thirteenth

Symposium (International) on Combustion, p. 745, The Combustion Ins t i tu te ,

Pittsburgh, Pa., 1971.

17. Frenklach, M., Lee, J.H., White, J.N. and Gardiner, W.C.: Combustion and

Flame 41_, 1 (1981).

18. Urtiew, P.A. and Oppenheim, A.K.: Proc. Royal Society A295, 13 (1966).

19. Urtiew, P.A., Brandeis, J . and Hogan, W.J.: Combustion Science and

Technology 30, 103 (1983).

TABLE CAPTION

TABLE I CHARACTERISTIC COMBUSTION PARAMETERS FOR FUEL-AIR MIXTURES. Thelaminar flame speed and c r i t i ca l tube diameter are for stoichiometric

composition. The chemical induction time correlations are from

Kistiakowsky and Richards15, Burcat et a l . 1 6 and Frenklach et a l . 1 7 for

C2H2, C3H8 and H2S, respectively.

TABLE I I Summary of Flame Acceleration Tests

A. 500 mm obstacles.B. 220 mm obstacles.

FUEL LAMINAR DETONATION

FLAME SPEEDa CRITICAL TUBE

(m/s) DIAMETER (m)

CHEMICAL INDUCTION TIME (sec)

T = K [FUEL]A [OXYGEN]B exp (EA/RT)b

K A B E (KJ/mole)A

Acetylene 12.1

(C2H2)

Propane

(C3H8)

Hydrogen

Sulphide

(H2S)

3.7

2.7

0.115 2.69x10-11 0 -1.0

0.9

71.58

3.92x10-12 0.57 -1.22 176.65

1.3C 2.29x10-15 -0.45 -0.33 109.67

a) Assumes velocity of burned gas is zero.b) Units: Concentrations, [FUEL] and [OXYGEN], moles/l i ter.

c) Estimate based on detonation cel l size.

SUMMARY OF FLAME ACCELERATION TESTS

TESTNO.

13

14

10

12

9

11

20

FUEL%

C 2 H 2

7.8%

C 2 H 2

7.5%

C3H84%

C3HB

4%

C3H84.14%

H2S9.3%

H2S12.9%

COMMENTS

A.

IGNITION

4 SPARKS

4 SPARKS

4 SPARKS

TUBE

4 SPARKS

TUBE

4 SPARKS

500 mm DIAMETER OBSTACLES

MAXIMUMFLAME SPEED

(m/sl

435 +

180 +

62

200

67

45

81

AVERAGE PEAK LAMINARFLAME SPEED OVERPRESSURE FLAME SPEED*

(m/sl (mbar) (m/s)

124 +

85 +

45

55

53

18

59

>155 +

132 +

86.2

>121

12.4

44.8

25.4

12.1

11.0

3.7

3.7

3.7

1.5

2.6

TEST NO. 13 - TRANSITION TO DETONATION AT THE END OF CHANNEL

TEST NO. 14 - IGNITION DUE TO HOT WIRE AT END LEADS TO ONSET OF DETONATION

TEST NO. 12 - MAXIMUM PRESSURE AND VELOCITY NEAR IGNITION END

TEST NO. 9 - CENTRAL OBSTACLES ONLY

TEST NO. 11 - APPEARS TO SLOW DOWN

+ PRE DETONATION VALUES

* ASSUMES VELOCITY OF BURNED GAS IS ZERO

U.

SUMMARY OF FLAME ACCELERATION TESTS

B. 220 mm DIAMETER OBSTACLES

MAXIMUM AVERAGE PEAK LAMINARNO % IGNITION FLAME SPEED FLAME SPEED OVERPRESSURE FLAME SPEED*

(mis) (m/s) (mbar) (m'sl

18

19

15

16

17

C2H25.17%

C 2H 2

7.71%

C 3 H 8

4.05%

C3H84.32%

H2S10.7%

COMMENTS

4 SPARKS

4 SPARKS

TUBE

4 SPARKS

TUBE

97

375 +

90

92

36

51

86 +

62

70

28.5

51.7

303 +

51.7

18.3

<7.4

12.1

3.7

3.7

2.1

TEST NO. 19 - TRANSITION TO DETONATION 10.7 m DOWN CHANNEL

TEST NO. 16 - NO PRESSURE RECORDS

+ PRE-DETONATION VALUES

* ASSUMES VELOCITY OF BURNED GAS IS ZERO

FIGURE CAPTIONS

Figure 1 Experimental Configuration: 500 mm obstacles

a) Sketch of Test Configuration

b) End View of Obstacles

c) Side View of Obstacles

Figure 2 Experimental Configuration: 220 mm obstacles

a) Sketch of Test Configuration

b) End View of Obstacles

c) Side View of Obstacles

Figure 3 Numerical Simulation of Flame Propagation Showing Distr ibut ion of

Veloci ty, Combustion Rate and Fuel Fraction for :a) Stoichiometric Acetylene-Air

b) Stoichiometric Propane-Air

Figure 4 Experimental and Numerical Results for Acetylene-Air Mixtures

a) Flame Velocity vs Distance

b) Peak Overpressure vs Distance

Figure 5 Selected Frames from High-Speed Film Record Showing Flame Acceleration

and Transit ion to Detonation in Acetylene-Air (7.7% C2H2) with 220 mm

Obstacles.

Figure 6 Selected Frames from High-Speed Film Record Showing Explosion and

Transit ion to Detonation in a Turbulent End-Pocket of Acetylene-Air

Prior to the Arr ival of the Main Flame Front.

Figure 7 Experimental and Numerical Results for Propane-Air Mixtures



Figure 8 Experimental and Numerical Results for Hydrogen Sulphide-Air Mixtures



Figure 9 Variation of Peak Overpressure with Scale. Scale of 1.0 Corresponds to

1.8 m x 1.8 m Cross-Section Channel, 15.5 m Long, with 500 mm

Obstacles.

77/777777//

CHANNEL SIZE: 1.8 m x 1.8 m IN CROSS SECTIONx 15.5 m LONG

PRESSURE TRANSDUCERS: SPACING = 1.27 m

OBSTACLESDIAMETER = 500 mmSPACING(S) = 1.27 mHEIGHTIHI = 0.90 m

^SUPPORT FRAME: DIAMETER = 60mm

a) SKETCH OF TEST CONFIGURATION

b) END VIEW OF OBSTACLES c) SIDE VIEW OF OBSTACLES

Figure 1

PLASTIC BAG

/ 12 11/ |

PLASTIC BAG

/ i l T /,'

CHANNEL SIZE. 1.8 m x 1.8 m IN CROSS SECTIONx 15.5 m LONG

DIAMETER = 220 mm

SPACING(S) = 0.63 m

PRESSURE TRANSDUCERS: SPACING = 1.27 m

- ^ OBSTACLES

—"SUPPORT FRAME: DIAMETER = 60 mm

al SKETCH OF TEST CONFIGURATION

b) END VIEW OF OBSTACLES c) SIDE VIEW OF OBSTACLES

Figure 2

T 248.60 MS

u diCLO I • inMAXIMUM VELOCITY. 269.90 m/s

VELOCITY

1—1 1—II—1 1—1

ur - l - rn i—\'i :'vrn

cci i i i

COMBUSTION RATE

a) ACETYLENE-AIR

FUEL FRACTION

T-421.90 MS

D •

• i—i \ ! r i ' ri ri 'ri r

MAXIMUM VELOCITY: 36.92m/s

•i—i rn i—i

VELOCITY

COMBUSTION RATE

FUEL FRACTION

b) PROPANE-AIR

Figure 3

DETONATION VELOCn220 mw OBSTACLES

(7 7% C.H..

• NUMERICAl

• ^

TRANSITION TODETONATION

a) VELOCITY VS DISTANCE

70

1 0 -

D l ;

0 0 1 -V

//

/ s

/ y

/ ~x

/ / - " '^

O500 mm OBSTACLES

' 7 B"t. C, H , F

ÙWO mm OBSTACLES

0 NUMERICAL

b) OVERPRESSURE VS DISTANCE

Figure 4

a) 117.5 ms b) 118.5 ms

c) 119.5 ms d) 119.8 ms

a) 168.2 ms b) 169.2 ms

vgi"-/.

e) 170.8 ms f) 171.1 ms

Figure 6

220 mm OBS7ACIES<«3% C,H,.

\ ^ 500mm OBSTACLES14% C.H.I

• fROM PRESSURE RECOUDS

— NUMERICAL

—I20


Û 500mm OBSTACLES <«"t C3HB.

D NUMERICAL


Figure 7

D 500 mm OBSTACLES

112 9"*, H.S.

00 7", H,S

- NUMERICAL

DISTANCE <m-


40 •

35-

3 0 -

25 •

|

tu 2 0 -c

sï 15-

>

10-

5 •

0 •

£> 500 mm OBSTACLES '12 9% H 2 S '

O 220 m m OBSTACLES MO 7°* M2S'

D NUMERICAL

A — \ ^ // \ N/

8 >0 12

DISTANCE lm(


Figure 8

15000

10000 -

co

J 1000 •D A C E T Y L E N E

O P R O P A N E

V HYDROGEN SULPHIDEzCOCOLUcea

100 -

104 6

SCALE {-)

10

Figure 9

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