THE INFLUENCE OF INJECTION PRESSURE AGAINST MISTCHARACTERISTICS OF DIESEL–DME MIXTURES FUEL

IN THE ENGINE

Bambang Suwondo RahardjoTechnology Center for Energy Resources Development

Deputy for Information, Energy and Material of TechnologyAgency for the Assessment and Application of Technology (BPP Teknologi)

BPPT II Building 22ndFl, Jl. M.H. Thamrin No. 8 Jakarta 10340Email: bamsr52@yahoo.co.id

ABSTRACT

Fuel mist injection plays a main role in determining the performance of dieselengines, where the mist pattern illustrates fuel combustion occurs in the combustionchamber. Characteristics of Sauter Mean Diameter (SMD) mist is devoted to fuelevaporation, and mixing and combustion quality affected by pressure injection (P)and the physical chemical properties of the fuel (density, surface tension, viscosityand boiling point). From fuel spray test results showed that fuel evaporationcharacteristics of fuel at a certain pressure effect on engine performance. The higherthe injection pressure will reduce the diameter of the fuel mist after injection (SMD),thus speeding up evaporation and mixing processes between fuel and air in thecombustion chamber with resulted the combustion process is more completely.

Keywords : Diesel-mix-DME fuel, injection pressure, engine combustionchamber

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1. INTRODUCTION

Development effortsalternative fuels as asubstitute for fuel oilbecome increasingly strongerdemands, where theconsideration for the makingof new alternative fuels thathave an impact on society,such as the impact ofgreenhouse gases, the amountof reserves, availability,convenience and compatibilitythe transport sector andother sectors use,infrastructure, economical,and safe [5].

Di-methyl ether (DME) isthe simplest ether compoundwith the chemical formulaCH3OCH3 known as organicsolvent extraction and themedia in the form of acolorless liquid aerosolpropellant for industrialuse. DME as a propellantwidely used as one of thedriving ingredient in theperfume industry, medicinemosquito repellent, personalcare (hair spray, foams,shaving cream,antiperspirants), colognes,room air fresheners, foodcoolants, industrial coating,paints and finishing as wellas automotive.

At ambient temperature andatmospheric pressureconditions is colorlessgaseous which has propertiesresembling propane (C3H8) andLPG. Whereas at ambienttemperature conditions with 6atm pressure or atatmospheric pressure with atemperature of -25ºC form acolorless liquid that can betransported and stored intanks at low temperaturessuch as LPG [4].

DME is highly flammable,without causing soot underany circumstances because theoxygen atoms contained in themolecule. DME is also a non–toxic chemicals or compoundsthat do not contain sulfur(S) and nitrogen (N) so thatemissions (SOx NOx,particulates and soot) aremuch lower than diesel(diesel) and do not damagethe ozone layer. In addition,DME is not corrosive tometals that do not requirespecial modifications to theexisting infrastructure ofLPG when used as areplacement or LPG mixer.

At low mole fraction (%volume low), this gas has avery strong scent and eventhough a high mole fraction(> 10% volume) has no effect

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on health, except the effectsof inhaling the drug afterlong periods of time, buteven then can be recognizedby the odor.

DME has a lower calorificvalue than LPG or LNG or ±65% of natural gas (CH4) or ±40% of MeOH, due todifferences in chemicalstructure, but the density ofliquid DME larger so that thetotal heating value of a tankDME ± 90% of the tank similarto LPG. Cetane Number (CN)high DME (55 ~ 60) is ameasure of the combustionquality of diesel fuel duringcompression ignition, so itcan be used as a substitutefor diesel fuel [2].

DME is currently beingprojected as a source ofenvironmentally friendlyalternative fuel, which canbe produced from syngasvarious sources of energy,such as coal, biomass andnatural gas. Syngas can beproduced through gasificationof coal / biomass or partialoxidation / steam methanereforming / auto-thermalreforming of natural gas.DME-making process there aretwo ways the process directly(direct process) and indirectprocesses (indirect process).

Direct process is a processof formation of syngas (CO +H2) which can be producedthrough gasification ofcoal / biomass or natural gaspartial oxidation process,then synthesized into DME.While the indirect process isa process that begins withthe manufacture of MeOH,followed by MeOH dehydrationin a separate reactorsynthesized into DME.

DME utilization means hasincreased economic value andas an effort to reducedependence on oil as well assolving the problem ofenvironmental pollution.Viewed from the comparison offuel prices, DME is stillcompetitive compared to LPGand diesel fuel. On the basisof energy equivalence, DMEproduction cost is lower thandiesel. However, thedifference in characteristicsbetween diesel and DME led tothe use of DME as a fuel indiesel engine injectionsystems require modificationof existing ones. DMEcombustion was not issuedbecause it contains oxygenand soot structure withoutforming chemical bonds ofcarbon.

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The advantage of DME showsthe potential to be analternative fuel in dieselengines, while theshortcomings to be appliedare a challenge that must beanswered through research.

In general, the combustioncharacteristics areinfluenced by two importantparameters, namely: injectionpressure (P) and physicalchemical properties of thefuel (density, surfacetension, viscosity andboiling point). At thebeginning of the injection(tasoi tb), or long distancemist penetration (S) isinfluenced by pressureinjection (P) and fueldensity (l), as defined byequation [1].

Equation [2] shows theempirical formula for long-distance or mist penetration(S) after the injectionprocess is complete (tasoi ≥tb), where the influence ofinjection pressure andphysical chemical propertiesof the fuel decreases evennone at all, while theinfluence of the density ofthe air around the enlarged.

Mist characteristics of SMD(Sauter Mean Diameter)devoted to fuel evaporation,mixing and combustionquality, is also influencedby pressure injection (P)and physical chemicalproperties of the fuel, asdefined by equation [3].

Based on the resultsrecorded images using adigital camera video showsthe interaction or theinfluence of injectionpressure and physicalchemical properties of thefuel to the fuel mistcharacteristics.

2. RESEARCH

Fuel mist test of Diesel,DME and Diesel-mix-DME

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m : Density m : Viscositym : Surface tension

A : Density ambient air

∆PL

:Injection pressure of mist

conducted at the LaboratoryInstitute of Technology Motorand Propolsi - PUSPIPTEK -Serpong.

The purpose of research isto test fuel mist of Diesel,DME and Diesel-mix-DME onpressure variation forinvestigating the combustioncharacteristics in theengine.

2.1. Materials

Table 1 and Table 2 showsthe fuel characteristics ofDME and diesel oilrespectively.

Table 1. Characteristic ofDME

Physical Properties DMEChemical Formula CH3-O-CH3

Molecular Weight g/mol 46C %

mass52.2

H %mass 13O %

mass34.8

Ratio C/H 0.337Critical temperature

oK 400Critical pressure MPa 5.37Critical density kg/m3 259Density of liquid kg/m3 667Relative density of gas (air=1)

1.59

Cetane number >55Auto-ignition temperature

oK 508Stoichiometric air/fuel mass ratio

9.0Boiling point at 1 atm

oK 248.1Enthalpy of evaporation

kJ/kg 467.13Lower heating value (LHV)

MJ/kg 27.6Specific heat capacityof gas

kJ/kgK

2.99Ignition limits %Vol

air3.4/18.6

Modulus of elasticity

N/m2 6.37E+0.8Kinematic viscosity ofliquid

cSt <1Surface tension (298 K)

N/m 0.012Vapour pressure (at 298 K)

kPa 530

Table 2. Characteristic ofDiesel Oil

Physical Properties DieselOilChemical Formula -

Molecular Weight g/mol 170C % mass 86H %mass 14O % mass 0Ratio C/H 0.516Critical temperature oK 708Critical pressure MPa 3.00a

Critical density kg/m3 -Density of liquid kg/m3 831Relative density of gas (air=1)

-Cetane number 40-50Auto-ignition temperature

oK 523Stoichiometric air/fuel mass ratio

14.6Boiling point at 1 atm oK 450 –

463Enthalpy of evaporation

kJ/kg 300Lower heating value (LHV)

MJ/kg 42.5Specific heat capacityof gas

kJ/kgK 1.7Ignition limits %Vol

air0.6/6.5

Modulus of elasticity N/m2 14.86E+08Kinematic viscosity of

liquidcSt 3Page 5 of 12

Surface tension (at 298 K)

N/m 0.27Vapour pressure (at 298 K)

kPa <<10

2.2. Equipments

Figure 1 shows the misttest equipment for Diesel,DME, and Diesel-mix-DME,comprising:

The fuel tank (1) forstorage (DME, diesel oil ordiesel-mix-DME) derived froma modified LPG cylinder onthe bottom that is made "legs" so that valves andnapple under the tank as thefuel flow not oppressed.

N2 gas tube (2) to give thefuel tank pressure above 5bar (20ºC) so that theliquid phase DME can beperfectly mixed with dieseloil, and to keep thepressure of DME suppliesinto diesel injection testerremains high.

Diesel injection tester (3)brand: Bosch, type: EFEP60H, pressure: 40 MPa fortesting mist fuel.

Diesel injector multi–hole (5holes) type direct injection (4)Isuzu Panther 2500cc withpressure max.18,5 MPa.

Backgorund screen is made ofblue fabric (5) in order tocapture the fuel mistpattern as it exits the fuelinjector by using a digital

video camera can be seenclearly.

2.3. Methods

Install the nozzle openingpressure test equipment.

Set the nozzle openingpressure on the pressuregauge by adjusting theinjector spring contraction.

Positioning the injector onthe hole in the screenbackground..

Pressing the pump leverdownward to start testing..

Take a photo or record achange in the pattern ofimages fuel mist using adigital video camera thatcan be clearly observed.

After testing is complete,remove the tubing connectorfrom the pump to theinjector, and then empty thefuel in it to prepare forthe next fuel mist testing.

Repeat these steps fortesting by variating of fueland mist pressure.

3. RESULTS AND DISCUSSION

3.1. Results

Figure 2, Figure 3, andFigure 4 respectively showthe mist pattern Diesel 100,Diesel–mix-DME 50/50, and DME100 at a pressure of 150 bar.

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Figure 5, Figure 6, andFigure 7 respectively show themist pattern of Diesel 100,diesel–mix-DME 50/50, and DME100 at a pressure of 180 bar.Figure 8, Figure 9, and

Figure 10 respectively showthe mist pattern of Diesel100, Diesel-mix-DME 50/50,and DME 100 at a pressure of235 bar

3.2. Discussion

3.2.1. Fuel mistcharacteristics at aninjection pressure of150 bar

At an injection pressure of150 bar, mist penetrationdistance (S) from Diesel 100is the longest (50cm), whileDiesel-mix-DME 50/50 around40cm and DME 100 is theshortest (30cm). Thedifferences mist penetrationdistance (S) is caused by theboiling point of DME (-25oC,1 atm) is much lower thandiesel (150-380oC, 1 atm), soDME is more volatile and tendto easily distributedsideways or going wide.Diesel granules with a higherboiling point will be morestable in a linear move inthe direction injectionpressure and tend to movestraight, thus resulting mist

penetration distance (S) islonger. Thus the highercontent of DME, mistpenetration distance (S) willbe getting shorter.

Another tendency thatarises is the higher contentof DME in the wide anglesolar mist formed; it isassociated with the movementof steam molecules DME anddiesel to the side. Thehigher DME content in the mixto make the process of mixingfuel and air is perfect sothere will be more perfectcombustion, it is caused bythe formation of steamquicker and more at the startfogging [1].

3.2.2. Fuel mistcharacteristics atinjection pressure of180 bar

At higher injectionpressure is about 180 bar,Kabutan penetration distance(S) is still relatively thesame as the injectionpressure of 150 bar. However,the injection pressureaffects the grain diameterafter fuel injected (SMD),especially at ambientconditions. The higherinjection pressure willreduce the diameter of fuel

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droplets after injection tofacilitate or accelerateevaporation. Figure 5 showsthat the mist pattern ofdiesel 100 more spreadindicated by fogging angle() is greater than theinjection pressure of 150 barin Figure 2. In Figure 6 andFigure 7 shows that thehigher the content of DME isgetting faster evaporationrates, as well as the greaterangle fogging (). Mixingprocess between the fuel andair in the combustionchamber, is getting better ata pressure of 180 barcompared to injectionpressure of 150 bar.

3.2.3. Fuel mistcharacteristics at 235bar pressure

At a pressure of 235 bar,fuel mist characteristicswill change significantlytheir extent, this is becausethe grain diameter of dieselwill become smaller, so thatthe rate of evaporation willbe faster [3]. Mistpenetration distance (S) onfuel fogging of Diesel 100 isstill influenced by pressureinjection (Figure 8),however, the influence ofinjection pressure was notsignificant on Diesel-mix-DME

50/50 (Figure 9) and DME 100(Figure 10). Injectionpressure will be moredominant effect on theincidence of mist (angle )and the rate of fuelevaporation. The mixing andcombustion process betweenDME with air is gettingbetter at a higher injectionpressure.

4. CONCLUSIONS

Testing the mistcharacteristics of diesel,DME and blends in injectionpressure variation of 150,180 and 235 bar using IsuzuPanther Diesel car injector2500cc direct injection type,it can be concluded that: The results showed footageof the interaction or theinfluence of injectionpressure and physicalchemical properties of thefuel against the fuel mistcharacteristics.

At an injection pressure of235 bar, mist penetrationdistance (S) Diesel 100 isthe longest (70 cm), thenthe Diesel-mix-DME 50/50approximately 40 cm and DME100 is the shortest (30cm).While the mist penetrationdistance (S) of fuel atinjection pressure of 150bar and 180 bar, shows the

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same, ie 50 cm (Diesel100),40 cm (Diesel-mix-DME50/50), and 30 cm (DME 100).

Differences mist penetrationdistance (S) due to theboiling point of DME (-25oC,1 atm) is much lower thanDiesel (150-380oC, 1 atm),so DME is more volatile andtend to be easilydistributed to the side orgoing wide.

The higher injectionpressure will reduce thediameter of fuel dropletsafter injection (SMD) thusspeeding evaporation andmixing process between thefuel and air in thecombustion chamber.

The higher content of DMEmist penetration distance(S) will be getting shorter,faster evaporation rates,the greater the anglefogging (), the mixingprocess fuel and air isperfect so there will bemore perfect combustion, itis caused by the formationof vapor over quickly andmore at the start fogging.

REFERENCES

[1]. Elana M. Chapman, etall, Annual TechnicalProgress Report forProject Entitled, Impact ofDME-Diesel Fuel Blend Properties

on Diesel Fuel Injection Systems,May 16, 2002 – May 15,2003, Report Issue Date:June 2003, The EnergyInstitute UniversityPark, The PennsylvaniaState University.

[2] Constantine Arcoumanis,Choongsik Bae, RoyCrookes, Eiji Kinoshita,The potential of di-methyl ether(DME) as an alternative fuel forcompression ignition engines: Areview. Fuel, Volume 87,Issue 7, June 2008, 1014–1030.

[3] Hyun Kyu Suh, Chang SikLee, Experimental andanalytical study on the spraycharacteristics of dimethyl ether(DME) and diesel fuels within acommon-rail injection system in adiesel engine, ElSEVIER,ScienceDirect,Mechanical Engineering,Hanyang University, 17Haengdang-dong, Availableon 5 July 2007.

[4] Myung Yoon Kim, SeungHyun Yoon, Bong Woo Ryu,Chang Sik Lee, Combustionand emsission characteristics ofDME as an alternative fuel forcompression ignition engines witha high pressure injection systems,Fuel, Volume 87, Issue

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12, September 2008, 2779–2786.

[5] Troy A. Semelsberger,Rodney L. Borup, Howard

L. Greene. Dimethyl ether(DME) as an alternative fuel,Journal of Power Sources,Volume 156, Issue 2, 1June 2006, 497–511.

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