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Procedure for Engine Transient Cycle Emissions 1
Testing in Real-Time 2
J Arregle, V Bermúdez, JR Serrano and E Fuentes 3
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CMT Motores Térmicos, Universidad Politécnica de Valencia, Camino de Vera, s/n, 46022 Valencia, 5
Spain 6
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Abstract 8
In this study, a procedure was applied for the performance of real-time emissions measurement at engine 9
transient tests. The measurement of gaseous emissions from raw exhaust was done according to the 10
standard ISO16183:2002 and the particulate mass emission was determined by an alternative method 11
based on the measurement of smoke opacity and hydrocarbon emission during the transient test for 12
further conversion to particulate mass. The method for calculating particle mass was validated by 13
comparison with experimental data obtained by application of the standard gravimetric method. 14
A measurement strategy, including engine preconditioning and control of ambient temperature, was 15
applied to improve measurements. For the analysis of results, the time misalignment of the measurements 16
was corrected by the calculation of the delay times produced as a result of the measurement systems 17
configuration. 18
The measurement procedure was applied to two cases of cycles UDC: with and without glow plug 19
inside the cylinder of a light duty Diesel engine. The time evolution of each pollutant was analyzed to get 20
understanding of which stages of the cycle produce more pollution and the comparison between both 21
cycles was done by using the exhaust emissions integrated during the tests. 22
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Keywords: transient test, exhaust emissions, Diesel engine, Urban Driving Cycle 24
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Nomenclature 29
CVS Constant volume sampling 30
DPM Dry Particle mass (g/kg fuel) 31
ECE Each segment of the UDC cycle 32
ECU Engine Control Unit 33
ESC European Stationary Cycle 34
ETC European Transient Cycle 35
EUDC Extraurban driving cycle 36
FSN Filter Smoke Number 37
HCLD Heated Chemiluminescent detector 38
HFID Heated flame ionization detector 39
ISF Insoluble Fraction 40
m Specific mass emission (g/kWh) 41
NDIR Non dispersive infrared absorption detector 42
PM Total particle mass emission (g/kg fuel) 43
SOF Soluble Organic Fraction 44
UDC Urban driving cycle 45
Mass concentration (kg/m3) 46
Subcripts 47
c dry soot 48
HC hydrocarbons 49
y mass fraction in fuel 50
p total particle mass 51
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1. Introduction 53
Due to the high level of atmospheric pollution caused by vehicle engine emissions the international 54
legislation has established over the years a series of tests to evaluate the potential capability to pollute of 55
different types of engines in order to impose restrictions to the commercialization of high polluting 56
engines. These tests have been designed with the purpose of simulating real engine operating conditions 57
by the performance of steady and transient test cycles. 58
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Tests cycles established by legislation specify the characteristics of the whole measurement system 59
necessary to perform the test, including measurement configuration, devices and procedures. The required 60
specifications differ in its conditions from steady to transient tests. 61
The test cycle defined by the European legislation for the certification of heavy duty engines at 62
stationary conditions is the ESC (European Stationary Cycle) cycle. For the performance of the ESC 63
cycle the engine is operated on an engine test bed at 13 operation modes defined by different settings of 64
load and speed. The modes are operated consecutively during the test and gaseous emissions and 65
particulate mass measurements are carried out for each mode. A fraction of the exhaust emitted by the 66
engine is sampled directly to measure concentrations of gaseous emissions (CO2, CO, NOx and HC). For 67
the particle mass measurement a small fraction of the exhaust flow is sampled to be diluted and cooled 68
with clean air in a partial or total flow dilution tunnel. The diluted flow is passed through a 69
preconditioned filter at a temperature below 52ºC and the particle mass emission is determined from the 70
weighting of the collected mass during the cycle. At steady conditions the real-time exhaust flow (g/h) 71
can be easily calculated by the addition of the constant intake air and fuel mass flows. The emitted 72
specific masses per hour (g/kWh) of gaseous and particulate emissions are calculated from the gas 73
concentrations measured and the particulate mass collected, by using the value of the exhaust mass flow. 74
The European transient cycles for heavy duty and light duty engines are the ETC and UDC+EUDC 75
cycles, respectively. The ETC (European Transient Cycle) cycle is based on real road cycle 76
measurements for heavy duty vehicles and it is performed on an engine dynamometer for certification 77
evaluations. Different driving conditions are represented by three parts of the ETC cycle, including urban, 78
rural and motorway driving. Each part has a duration of 600 s and the entire cycle has a duration of 1800 79
s. 80
Light duty engines are certified by the UDC+EUDC cycle, which is performed on a chassis 81
dynamometer. The UDC cycle (Urban Driving Cycle) includes four equal urban segments called ECE, 82
performed continuously, followed by one Extraurban Driving Cycle (EUDC). The UDC cycle was 83
designed to represent city driving conditions, and it is characterized by low vehicle speed, low engine 84
load, and low exhaust gas temperature. The EUDC (Extra Urban Driving Cycle) segment has been added 85
after the fourth ECE cycle to simulate more aggressive, high speed driving conditions. 86
The current legislation establishes the CVS (Constant Volume Sampling) system as the standard 87
sampling system for the performance of transient tests for heavy and light duty engines. It consists in the 88
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dilution of the total exhaust flow with clean air in a dilution tunnel, by keeping constant the resultant 89
diluted flow by means of a pump system. A small fraction of the CVS flow is sampled into a bag, thus the 90
bag performs an average over the test. After the test, the concentrations of the gases in the sample inside 91
the bag are measured by means of a gas emission bench. For the particle mass measurement a sample of 92
the total flow from the dilution tunnel is extracted and passed through filters where the particles are 93
collected. The particle emission is determined from the total particle mass collected onto the filters during 94
the cycle. For comparison with the standard limits an average over the test (g/test or g/km) is calculated 95
for both gaseous and particle emission. The use of the CVS system has important drawbacks due to the 96
high space and cost requirements that the dilution of the total exhaust flow implies. 97
In this context, it has recently been published the standard ISO 16183:2002 [1], whose purpose is to 98
provide an optional measurement procedure for the performance of transient tests on a test bed, based on 99
the real-time measurement of gaseous emissions from raw exhaust, while particle mass measurement is 100
carried out by using a partial flow dilution system. The application of this standard allows the 101
replacement of the CVS type systems by partial flow dilution systems and it can be considered as an 102
option to the regulated measurement procedure for the performance of test cycles with the approval of the 103
certification agency. The standard can be applied to any transient test cycle that does not require extreme 104
system response times and it establishes a quality assurance with highly sophisticated verification of the 105
measurement procedure. 106
Although the measurement of gases from the raw exhaust and the use of a partial flow dilution 107
system for the measurement of particle mass proposed by the referred standard imply important 108
advantages compared with the use of the CVS system, a series of new problems arise due to the 109
characteristics of the alternative measurement method. Firstly, a partial flow dilution system for 110
measuring particle mass emissions could replace the CVS system only if a high correlation exists (≥0.9) 111
between the sample flow of the dilution system and the total exhaust flow. In addition, since exhaust 112
gases concentrations have to be measured in a real time basis, different delay times exist between the gas 113
concentration and the air and exhaust flow measurements, resulting in a misalignment between the 114
registered data. For the gas emission calculation, it is necessary to correct this misalignment, since if it is 115
not corrected it could result in large deviations of the final results. 116
The aim of this work is to present an efficient method to perform exhaust emission measurements at 117
engine transient conditions in an environment close to that accepted for engine certification. The 118
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measurement of gaseous emissions from raw exhaust was done according to the standard ISO16183:2002, 119
while the particle mass emission was determined by an alternative method based on calculating 120
particulate mass from opacity and hydrocarbon measurements, instead of using the standard gravimetric 121
method. Since opacity measurements are highly related with the amount of carbonaceous particulate 122
matter in the exhaust and the soluble fraction of particulate matter is related to hydrocarbon compounds, 123
opacity and hydrocarbon emission measurements could be used to calculate the total particle mass 124
emission. This alternative procedure could replace the use of a partial flow dilution system, thus reducing 125
cost and operation requirements. Another advantage of the determination of real-time particulate mass 126
from opacity and hydrocarbon measurements is that it allows to obtain the time evolution of the 127
particulate emission during the transient cycle and not only to have the total particle mass collected by the 128
gravimetric method. Thus, a deeper analysis of those stages that produce higher particle emission during 129
the transient test can be achieved. This different method for calculation of particulate mass was validated 130
by comparison with particle mass measurements obtained by application of the gravimetric method after 131
diluting with a partial flow dilution minitunnel. 132
A measurement strategy, including engine preconditioning and control of ambient temperature, was 133
applied to improve measurements repeatability. For the analysis of results, the time misalignment of the 134
measurements was corrected by calculating the different delay times produced by the measurement 135
configuration. 136
The measurement method was applied to two cases of UDC cycles: with and without glow plug 137
inside the cylinder of a light duty Diesel engine. The time evolution of each pollutant was analyzed to 138
identify the stages of the cycle producing more pollution and the comparison between both cycles was 139
also done by using the total emission of gases and particle integrated during the tests. 140
2. Experimental. 141
2.1. Engine and measurement systems. 142
A HSDI turbocharged Diesel engine was run for the test cycle and a Diesel standard #2 commercial 143
fuel type was used. Table 1 shows the specifications of the engine. The engine was fully instrumented, 144
and the transient cycle was programmed in a test cell control software and executed by a variable 145
frequency fast response dynamometer. 146
The amount of fuel consumption was determined by a fuel gravimetric system with an AVL 733S 147
Dynamic Fuel Meter. The measurement device consists of a measuring vessel filled with fuel that is 148
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suspended on a balance system. The fuel consumption values are obtained by calculating the vessel’s time 149
related weight loss with an accuracy of 0,12% at 75 g in accordance with DIN 1319. 150
A hot-film anemometer system Sensyflow P Sensycon was used to measure air mass flow. The 151
measurement range is 0-720 kg/h with an accuracy of 2% of the measured value. 152
A data acquisition system was employed to registry the data from all emission equipment and from 153
the engine control system, with a frequency higher than 10 Hz. 154
2.2. Emissions measurement 155
Gaseous test bench. 156
A scheme of the experimental set-up for the exhaust emissions measurement is shown in Figure 1. For the 157
measurement of gaseous emissions a gas test bench HORIBA 7100DEGR was used. The HORIBA 158
analysers specifications, measuring ranges and response time are adequate to the requirements established 159
by the standard ISO16183 for measuring the concentrations of the exhaust gas components under 160
transient conditions. The sample line of the equipment is connected directly to the exhaust pipe and it is 161
heated to maintain a wall temperature around 191ºC and avoid the condensation of hydrocarbons into the 162
line. The line is extended from the exhaust pipe to the equipment units where the different analysers are 163
located. The hydrocarbon analyser is a heated flame ionisation detector (HFID) type, with detector, 164
valves, pipework, etc. heated so as to maintain a gas temperature of 190±10ºC. Oxides of nitrogen are 165
measured on a dry basis, by means of a heated chemiluminescent detector (HCLD) type with a NO2/NO 166
converter. The sampling path is maintained at a wall temperature of 190±10ºC up to the converter. The 167
carbon monoxide and dioxide are measured with an analyser of the non-dispersive infrared (NDIR) 168
absorption type, while a paramagnetic detector was employed for the measurement of O2 concentration in 169
the exhaust flow. 170
Particulate matter and smoke measurement. 171
The Diesel particle matter collected on a filter after the dilution process consists of two main parts 172
after extraction with an organic dissolvent. The soluble fraction is called soluble organic fraction (SOF) 173
and is composed by hydrocarbons coming from the unburnt fuel and oil that have undergone a gas-to-174
particle conversion after dilution and cooling by nucleation and condensation/adsorption processes [2]. 175
The insoluble fraction or dry soot (ISF) mainly consists of carbonaceous matter and ash and represents 176
the majority of the mass of the total particulate matter (PM) [2]. 177
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According to the standard ISO16183, the particulate matter can be measured by means of a partial 178
flow dilution system, if a high correlation exists between the diluted sample and the exhaust flows. In this 179
study, an alternative method was employed to obtain the particle mass indirectly from real-time exhaust 180
smoke opacity and hydrocarbon emission measurements, instead of using the standard gravimetric 181
method. 182
A partial flow opacimeter AVL439 was used to measure continuously the smoke opacity of a sample 183
of the exhaust flow. Smoke density is a result of the opacity of black smoke (soot particles), blue smoke 184
(hydrocarbon vapour) and white smoke (water vapour). For the measurement, a sample of the exhaust 185
flow is continuously extracted and conditioned by a conditioning tube heated at 100ºC to prevent 186
hydrocarbon condensation and particles deposition. The opacimeter measuring chamber of a defined 187
measuring length and non-reflecting surface, is filled homogeneously with the extracted sample of 188
exhaust gas. The opacity of the sample is determined from the measurement of the attenuation of visible 189
light by the smoke in the air sample located between a source and a light detector which are sited at both 190
edges of the measuring chamber. 191
Another method to determine the amount of soot in the exhaust is the estimation of the so-called 192
filter smoke number (FSN). The method is based on extracting a volume of exhaust gas that is passed 193
through a filter paper. The blackness of the paper produced by the black carbonaceous particles is 194
detected with a reflectometer and the measurement is obtained by comparison with a reference. The FSN 195
units range in a scale from 0 to 10. The device used for measuring FSN was an AVL415 smokemeter. 196
In order to validate the method for calculating particle mass from opacity and hydrocarbon 197
measurements, a series of experiments were carried out to obtain particle mass emission with the 198
gravimetric method by using a dilution minitunnel AVL-SPC472. The dilution tunnel principle operation 199
consists in the extraction of a sample from the exhaust flow, which is mixed with clean air. The resultant 200
diluted flow is passed through a filter at a temperature lower than 52ºC and the particle mass specific 201
emission is determined from the particle mass collected onto the filter. 202
3. Particle mass calculation method. 203
Experiments at stationary conditions were carried out with simultaneous measurement of opacity, 204
FSN, exhaust gases concentration and particle mass, in order to validate the method for calculating 205
particle mass emissions from HC and smoke opacity measurements. The particle mass collection on the 206
filter was done at 48ºC after diluting at a dilution ratio of 20. 207
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Results in Figure 2 show a good correlation between opacity and FSN measurements. This trend 208
suggests that opacity measurement is highly related to measurement of the smoke number, which means 209
that the opacity measurement is dominated by the carbonaceous soot particle concentration in the exhaust, 210
i.e. by black smoke. 211
FSN measurements cannot be obtained continuously during transient measurements due the nature of 212
the smokemeter measurement principle. On the contrary, opacity measurements can be obtained during 213
transient tests, since a continuous flow of the exhaust is sampled. Nevertheless, opacity measurements 214
from transient tests can be converted to FSN units by using the correlation that exists between both 215
measurement units. 216
Some correlations to transform FSN units to particle mass of dry soot (i.e. carbonaceous particles) can 217
be found in the literature [3][4]. In addition, since the particulate mass collected on a filter after the 218
dilution process is composed by hydrocarbon matter (SOF) and carbonaceous matter (ISF), different 219
correlations have been proposed for determining the total particle mass (PM) from FSN and gaseous 220
hydrocarbon measurements [5][6][7]. In this study, these correlations were considered for the calculation 221
of the particulate mass, along with a new empirical one, product of this work (Table 2). Most correlations 222
for calculation of the total particle mass consist of an equation of two terms [5][6][7]. The first one is 223
related to the dry soot mass multiplied by a factor close to one, which means that most of the soot mass 224
associated to opacity measurements is nearly the same mass of carbonaceous soot collected onto the 225
dilution system filter. The second term is related to the mass of SOF, formed from the gas-to-particle 226
conversion of HC that takes place as a consequence of dilution and cooling of the exhaust gas. 227
Comparison between the particle mass estimated from smoke measurements by means of the 228
correlations for dry soot calculation and the experimental total particulate mass data obtained with the 229
gravimetric method are shown in Figure 3. Although it would be expected that the predicted values were 230
below the experimental data of particulate mass, the predictions approach the experimental values when 231
the particulate mass is below 0.30 mg/kg fuel. Values of mean deviations of these predictions with respect 232
to experimental data are shown in Table 3. The correlations for dry soot mass only account for the 233
carbonaceous matter in particle emissions. Hence, they are conceptually incomplete since they are not 234
taking into account the contribution of the SOF fraction to the total particle mass. 235
In order to add the volatile fraction mass to the dry soot mass predictions, the correlations for dry soot 236
were combined with the ones that include the SOF fraction contribution. Figure 4 shows the results of the 237
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correlations of total particulate mass [5][6][7] along with the empirical equation proposed in this study, in 238
comparison with the experimental data. Most of the correlations overpredict the experimental values of 239
total particulate matter, while the best fits, by comparing the mean deviations in Table 3, correspond to 240
the Lapuerta et al. [7] correlation combined with the Christian et al. [4] one, as well as the empirical 241
correlation proposed in this study. These two correlations could be used to calculate particle mass 242
emission from FSN and HC measurements. 243
Although the study of the correlations has been conducted at engine stationary conditions, such 244
correlations could be applied at transient conditions. The relationship between smoke opacity and 245
carbonaceous particle mass is directly related with the composition properties of the exhaust particles, 246
thus if the correlations are correct, the relationships should be independent of the engine operating 247
conditions. In addition, a transient cycle could be considered as a sequence of quasi-stationary process 248
with regards to particle formation, since the combustion and injection characteristic times are very short 249
compared with the time scale for the change in the engine conditions at transient conditions. Hence 250
validity of the correlations at stationary conditions could be extrapolated to transient cycles. 251
Since the smokemeter cannot be used at transient conditions, opacity measurements can be carried out 252
continuously during the transient tests for further conversion to FSN by using the correlation found 253
between opacity and FSN units shown in Figure 2. Finally, a correlation for total particle mass calculation 254
from HC measurements and the FSN values can be used. The empirical correlation proposed in this work 255
was employed for the calculation of particulate mass. 256
4. Measurement strategy and daily test schedule. 257
Measurement strategies are necessary in an environment such as engine emissions experimental 258
research, as many dispersion factors able to introduce variability exist. 259
In the European directive 91/441/EEC that specifies the UDC cycle there is not an explicit procedure 260
for the preconditioning of the engine before running a transient test. The only specification in the current 261
European emission legislation for the performance of transient tests is the regulation of ambient 262
temperatures above 20ºC. Nevertheless, a preconditioning procedure to limit the influence of external 263
factors is vital and necessary in order to get good repeatability. 264
During the transient test, a fraction of the particles will be lost due to deposition in the tailpipe walls 265
as a consequence of mechanical processes. In most cases the fraction of particles deposited on the walls is 266
negligible and it would not suppose an important problem if the particles stayed fixed on the walls. The 267
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reentrainment of these particles from the walls is the cause of variability in the particle emission 268
measurement, as the release of accumulated particles is unpredictable. Some mechanical processes 269
leading to particles deposition on exhaust pipe walls are inertial effects in bends and contractions that can 270
produce the deposition of particles unable to follow the streamlines, the diffusion of particles through the 271
boundary layer to the walls and phoretic effects. Thermophoresis is a source of variability in the 272
measurement of particulate and HC at cold start conditions. This phenomenon is due to the existence of a 273
temperature gradient between the exhaust system walls and the exhaust gas at cold start conditions. As a 274
result, the particulates are driven to the walls and deposited there. During the transient cycle these 275
deposits may be blown with the release of particles and condensed HC, affecting the measurements. This 276
occurs until a thermal equilibrium between the gas and the walls is reached in the exhaust system. Engine 277
conditioning prior to running a test can stabilize this process and reduce variability [8]. Although 278
measurements of particle in engines are always underreported due to deposition of particles in the 279
exhaust, the use of preconditioning periods is necessary in order to reduce the variability of the 280
measurements and obtain conclusions from engine research studies. 281
A preconditioning procedure at high speed and high temperature can be applied to remove deposited 282
particles into the exhaust system the day prior to the test, so particulate deposits in the exhaust pipe walls 283
are blown out [9] and the release of particles during the transient test is partially reduced. In addition, 284
catalyst efficiency has been found to be dependent on the preconditioning period thus, the definition of a 285
preconditioning procedure becomes necessary. 286
In order to remove deposits of particulates and hydrocarbons in the exhaust system, a preconditioning 287
period of 15 min was carried out the day prior to the test by running the engine at 3500 rpm and 75% 288
load. Thus, high temperatures and very low opacity level were maintained in the exhaust system during 289
the conditioning phase. 290
Ambient conditions are an important influential factor in emissions measurement. The highest amount 291
of emissions is produced at the first part of the test, due to the cold start conditions. In this situation 292
ambient conditions are highly influential factors which can have an effect on the production of pollutants. 293
Thus, ambient conditions should be controlled in order to reduce measurement variability. 294
In addition, it must be taken into account that hydrocarbon emissions measurements are very sensitive to 295
temperature changes due to hydrocarbon condensation-evaporation processes in the exhaust system. 296
Although the condensation of HC cannot be prevented due to the low temperatures reached in the current 297
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transient test cycles, more repetitive measurements will be obtained if ambient temperature is controlled 298
for all the tests performed. An external conditioning fan system was used to maintain a constant 22$1ºC 299
room temperature during the transient cycle in order to reduce the influence of the ambient temperature. 300
In addition, the initial oil and water temperatures were controlled aiming to get the same evolution of 301
temperatures at every transient cycle in order to improve the repeatability of the cycles. 302
A measurement strategy and a same daily test schedule were followed for each test. As a summary, 303
the procedure included: 304
- Exhaust and engine preconditioning during a period of 15 minutes at 3500 rpm and 75% of load the day 305
prior to the test. 306
- Ambient air temperature control at 22ºC. 307
- Initial oil, water and air temperatures equal to 22ºC. 308
- Controlled evolutions of engine oil and water temperatures. Fixed cooling circuit with engine thermostat 309
control. 310
- To warranty the reliability of the measurements one transient cycle was estimated as an average of two 311
repetitive tests. 312
5. Analysis of results. 313
5.1. Repeatability analysis and alignment of measurements. 314
The experimental procedure was applied to an UDC cycle without glow plug inside the engine 315
cylinder. During the test cycle performed, the time evolution of the air and fuel mass flow, the gas 316
concentration and opacity of the exhaust flow and the different engine operating parameters were 317
registered. For the calculation of the gaseous pollutant mass flow in grams per second the exhaust mass 318
flow was calculated by adding the intake air and fuel mass flows. 319
Repeatability of measurements was evaluated by comparing the exhaust emissions measurements on 320
three different days. Figure 5 shows the measurements of exhaust gases and smoke opacity during the 321
same transient test for the case without glow-plug on different days. The patterns show an acceptable 322
repeatability, with maximum variations of the total emission about 2% for NOx, 5% for THC, 7% for CO 323
and 3% for smoke opacity. 324
The provided exhaust flow data were not aligned with the concentration of gases measured due to the 325
delay caused by the transport time of the exhaust gases from the engine to the analyser and the intrinsic 326
response time of the gas analysers [10]. 327
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The total time of transport includes the time needed to transport the gases from the outlet of the engine 328
to the sample probe, plus the time of transport from the sample probe through the sampling line to the 329
measurement instrument and finally, to the corresponding analyser. The time needed for the transport 330
from the sample probe to the gas analyser is defined as delay time. The response time of an analyser once 331
the gas has reached it, is defined as rise time and it is considered as the time between the 10% and the 332
90% response of the final reading [1]. 333
The location of the analysers with respect to the engine influences the delay time due because of the 334
transport necessary through the sample line to these analysers. The HORIBA instrument for gas analysis 335
consists of two measurement units. NOx and THC gases are measured inside the same heated unit sited 336
closer to the engine than the unit where the rest of gases are measured (CO,CO2,O2) (Figure 1). 337
Delay times were calculated by application of the cross correlation method, following the approach of 338
Messer et al. [10]. The delay times calculated for the measurement of THC and NOx resulted 4.5 and 9.5 339
s, respectively, while the delay time for the measurement of CO was 34 s. The delay time for CO resulted 340
quite longer than the estimated for NOx and THC, since the analyser for CO measurement is sited at more 341
distance from the engine. Hence, the transport time for CO measurement is the longest. 342
The rise time of the gas analysers is about 3 s according to the specifications of the manufacturer. 343
Thus, the transport time was approximately of 31 s for CO and 4.5 and 6.5 s for THC and NOx, 344
respectively. Time shift for all emissions was done according to the calculated misalignment time as 345
illustrated in Figure 6. 346
6. Application of the methodology to the UDC cycle. 347
After the misalignment of the pollutants measurements with respect to the exhaust mass flow is 348
corrected, the trends in the production of pollutants during the transient cycle can be analyzed. The 349
analysis can be done by observing the time evolution of the emissions in the different stages of the cycle 350
and establishing relationships with variables such as air and fuel mass flow rates, engine speed and 351
temperatures [11][12]. 352
As an example of application of this methodology, an UDC cycle with glow plug inside the engine 353
cylinder was run and compared with the same case without glow plug. This example was chosen because 354
is a common practice in Diesel engine design to keep the glow plug switched on for certain time after 355
engine is started [13][14][15]. In the engine used, the glow plug is connected during 420 seconds. When 356
the engine is started the glow plug consumes a peak of power of about 1200 W and 30 seconds after this 357
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peak, the consumed power is progressively reduced to 550 W. The extra energy consumption due to the 358
glow plug activation during these 420 seconds is about 220 kJ. 359
The purpose of the late switching off of the glow plug is reducing the warm-up time of the engine, 360
during which severe increase of some pollutants emission, as HC and CO, is produced with respect to 361
stabilized conditions [12][16[18]. However, this technique has several drawbacks with respect to other 362
engine pollutants, such as particulate and NOx emissions. 363
Water and oil temperatures evolution during the test cycle can be observed in Figure 7. No significant 364
differences in time to reach the target water temperature can be seen in these charts between the cases 365
with and without glow plug. Therefore, the warm-up time reduction will be more related with the control 366
of pollutants emissions, than with the increment in the temperature of the engine fluids. 367
The evolution of the pollutants measured upstream the catalyst for the two cases studied is compared 368
in Figure 8. In this figure, the corrections explained in previous sections have been applied. Apart from 369
the HC, CO and NOx measurements it can be observed the PM emission obtained from the correlations 370
employed, based on opacity and HC emission measurements. The vehicle speed during the UDC cycle is 371
also plotted in this figure in order to make easier the comparison between the pollutants pattern and the 372
phases of the UDC cycle. Figure 9 represents the accumulated mass of gaseous and particle emissions 373
during the UDC cycle for the two cases considered. 374
NOx is produced in environments of high oxygen and nitrogen concentrations at high flame 375
temperature conditions. Hence, in Figure 8 it can be observed for both cases with and without glow plug 376
that the NOx emission are more important during the accelerations of the vehicle, as a result of the EGR 377
valve closing and the higher quantity of fuel injected [19]. The first phenomenon causes a reduction of 378
CO2 in the intake air, which means an increase of the O2 concentration in the combustion mixture, while 379
the increase in fuel injection causes a rise in the temperature. Therefore, an increase in the NOx amount is 380
produced. As a result of this, it is clearly appreciated in the accumulated NOx emission of Figure 9 that 381
each increase in NOx emission coincides with an engine acceleration. During cruise phases, the EGR 382
valve is open until its set point value and, consequently, the NOx emissions are reduced. For instance, the 383
effects of acceleration described above can be observed in the NOx chart in Figure 8 at 60 seconds from 384
the UDC start, while the effects produced during engine cruise phases can be seen in the 60 to 100 385
seconds period. When decelerating, very little amount fuel is injected, resulting in a sharp decrease in the 386
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NOx emission. Thus, NOx emissions could be considered roughly proportional to the mass of fuel 387
injected [17]. 388
The above described pattern of NOx emissions is repeated for the four ECE of the UDC cycle. In the 389
NOx chart in Figure 8 is shown that, with and without glow plug, during the 200 seconds of the first ECE 390
the level of NOx are significantly higher that for the rest of the ECE segments in the cycle. The reason for 391
this is the longer ignition lag produced by the lower temperatures in the combustion chamber, which 392
causes higher rates of heat release at the initial stage of combustion, as also conclude other authors [18]. 393
By considering this phenomenon, it is possible to explain the differences between the NOx emissions 394
with or without glow-plug. In the NOx chart in Figure 8 it can be seen that at the beginning of the UDC 395
cycle, during the first 30 seconds of the UDC, a high increase of NOx emissions is produced for the glow 396
plug case. This 30 seconds phase coincides with the peak of power in the glow plug (1200 W), previously 397
referred. Therefore, the higher NOx emissions are consequence of the higher quantity of fuel injected due 398
to the high electrical power dissipated in the glow plug during these 30 seconds. This has two effects, 399
additional closing of the EGR valve, due to the engine control unit (ECU) response to the higher fuel 400
amount injected [19], and higher rates of heat release due to the low combustion chamber temperatures 401
and the increase of fuelling. These low temperatures in the combustion chamber along with higher fuel 402
injection, in the glow plug case, are also the cause of higher NOx emissions with respect to the 403
configuration without glow plug, observed during the first ECE. This trend is observed not only at engine 404
accelerations but also during cruise phases (Figure 8). It can also be seen that the differences between the 405
two studied cases do not completely disappear until the glow plug is switched off about 420 seconds after 406
the UDC starting. 407
Conversely to NOx formation, hydrocarbons and CO are produced at conditions of defect of oxygen 408
and low temperature as a result of the partial oxidation of the hydrocarbons coming from the fuel. 409
According to this, during cruise phases there is an increase in the HC and CO emissions because of the 410
higher rates of EGR entering the cylinders and the reduction in the amount of the fuel injected, with the 411
consequent reduction of combustion temperatures. On the same basis, during accelerations and 412
decelerations, there is a reduction of these pollutants, since both the air mass flow entering the system and 413
the temperature increase. At idle conditions the oxidation rate of HC and CO is specially low due to the 414
low temperatures, which results in an increase of the concentration of HC and CO gaseous emissions in 415
the exhaust. 416
15
By comparing the cases of connected and disconnected glow plug it is observed a reduction of HC and 417
CO during the 420 s the glow-plug is connected, especially during the first 200 seconds period (first ECE 418
segment of the UDC). This is a result of the higher quantities of fuel injected increase combustion 419
temperatures, heating the cylinder walls and favouring HC and CO oxidation. 420
Particulate mass emissions are mainly controlled by the increase of fuel mass flow during engine 421
accelerations as observed in opacity and PM charts in Figure 8. More precisely, particulate emissions 422
raise in those stages in which the relative fuel to air ratio is increased. Therefore, when comparing the PM 423
emissions of the UDC performed with or without glow plug, it is clear that the smoke opacity is highly 424
increased during idle phases. This is a consequence of the extra fuel injected, which is not be very high in 425
value, but enough to significantly increase the fuel to air ratio at idle conditions. In addition, at these 426
conditions the low combustion temperatures reduce soot oxidation. For instance, this effect can be 427
observed in opacity and PM charts of Figure 8 at the idle phase between 100 and 125 seconds. The rest of 428
the idle phases of this chart show the same trend until the 420 seconds, time at which the glow plug is 429
switched off and the effect totally disappears. 430
Another effect favouring the increase of smoke opacity in the glow plug configuration case is the fuel 431
impingement against the hot-point that the glow plug becomes inside the engine cylinder. This effect is 432
continuous while the glow plug is switched on and it may explain the differences observed in opacity and 433
PM at other conditions of the UDC different than idle phase. 434
As a summary, the result of the electrical energy dissipated in the glow plugs, is an extra fuel injection 435
during the coldest part of engine warm up, which affects EGR valve opening (due to ECU strategies) and 436
increases the rates of heat release during the initial phases of the cycle. As a consequence, NOx, PM and 437
the fuel consumption are raised during the cycle, while HC and CO are reduced. Once the glow plug is 438
disconnected, the evolution of the pollutants becomes almost the same as the case without glow plug. 439
Figure 9 shows the accumulated mass of pollutants during both cycles. It is observed a reduction of 440
18% for HC and 21% for CO for the case of glow plug with respect to the case without glow plug. 441
However, an increase of 9% for NOx and a significant one for smoke opacity are detected. If the smoke 442
opacity is converted into particle mass emission an increment of 70% for particulate mass can be 443
quantified. An increment of 2% in the fuel consumption (Figure 10) is produced due to the extra load of 444
the engine when the glow plug is employed. 445
7. Summary and conclusions. 446
16
In this study, a measurement procedure was applied for the performance of in real-time emission 447
measurement at engine transient tests. Measurement of gaseous emissions from raw exhaust was done 448
according to the standard ISO16183:2002, while the particulate matter emission was determined by an 449
alternative method based on the measurement of smoke opacity and gaseous hydrocarbon emission for 450
further calculation of the total particulate mass. The use of this method instead of a partial flow dilution 451
system to determine particle mass emission implies less cost and operational requirements and in addition 452
it allows obtaining a real-time evolution of particle emission during the transient cycle. A revision of the 453
existing correlations to calculate dry soot and total particle matter from smoke and gaseous hydrocarbon 454
measurements was done and a new correlation was proposed for the determination of particulate mass. 455
Validation of the calculation particulate mass method was achieved by comparison with experimental 456
total particle mass measurements at stationary conditions. 457
A measurement strategy, including engine preconditioning and control of ambient temperature, was 458
applied to improve measurement repeatability. In addition, the misalignment of real-time measurements 459
was corrected. 460
The experimental procedure was applied for the performance of two different cases of Urban Driving 461
Cycle transient tests: with and without glow plug inside the cylinder of a light duty Diesel engine. The 462
effect of the heating due to the connection of the glow plug was observed to produce a reduction in the 463
hydrocarbon and CO emissions with an increase of the amount of NOx and PM emitted. 464
The proposed measurement technique has been proved to be an adequate and efficient method to 465
perform engine transient tests cycles for research works in an environment very close to that accepted for 466
engine certification. 467
References 468
[1] Heavy duty engines- Measurement of gaseous emissions from raw exhaust gas and of particulate 469
emissions using partial flow dilution systems under transient test conditions (2002). ISO 16183:2002. 470
[2] Kittelson D.B., Watts W.F., Arnold M., Review of Diesel Particulate Sampling Methods, Final report 471
Aerosol Dynamics, Laboratory and on-road studies, Univ. Minnesota Dep. Mech. Eng (1998). 472
[3] Alkidas A.C., Relationships between smoke measurements and particulate measurements, SAE paper 473
840412, 1984. 474
[4] Christian V.R., Knopf F., Jaschek A., Schindler W., Eine neue Mebmethodik der Bosch-Zahl mit 475
erhörter Empfindlichkeit, MTZ 54, (1993). 476
17
[5] Greeves G., Wang C.H., Origins of Diesel Particulate mass emission, SAE paper 810260, 1981. 477
[6] Arcoumanis C., Megaritis A., Real-time measurement of particulate emissions in a turbocharged DI 478
Diesel engine, SAE paper 922390, 1992. 479
[7] Lapuerta M., Armas O., Hernández J.J. Ballesteros R., Estimation of Diesel particulate emissions 480
from hydrocarbon emissions and smoke opacity, THIESEL 2002 Conference on Thermo-and Fluid 481
Dynamic Processes in Diesel Engines, Valencia September 10th -13th
, Conference Proceedings ISBN 84-482
9705-233-1 (2002) 215-225. 483
[8] Kittelson D.B., Johnson J.H., Variability in Particle Emission Measurements in the Heavy Transient 484
Test, SAE paper 910738, 1991. 485
[9] Andrews G.E., Clarke A.G., Rojas N.Y., The transient storage and blow-out of Diesel particulate in 486
practical exhaust systems, SAE paper 2001-01-0204, 2001. 487
[10] Messer J.T., Clark N.N., Lyons D.W., Measurement delays and modal analysis for a transportable 488
heavy duty emissions testing laboratory, SAE paper 950218, 1995. 489
[11] Knecht W.,Exhaust gas after-treatment techniques to reduce nitrogen oxides from heavy duty Diesel 490
engines ATA-Ingenieria Automotoristica, 50 n 8/9 (1997) 443-449. 491
[12] Bielaczyc P., Merskisz J., Cold Start Emissions Investigation at Different Ambient Temperature 492
Conditions , SAE paper 980401, 1998. 493
[13] Bardon M.F., Gardiner D.P., Rao V.K., The potential of new technology to reduce automotive cold 494
start and warm-up emissions, IMechE C389/395 925026 (1992 ) 75-87. 495
[14] Cooper B., Jackson N., Penny I., Rawlins D., Truscott A., Seabrook J., Advanced Combustion 496
System Design, Control and Optimisation to Meet the Requirements of Future European Passenger cars 497
THIESEL 2004 Conference on Thermo-and Fluid Dynamic Processes in Diesel Engines. Valencia 498
September 7th -10th 2004. Conference Proceedings ISBN 84-9705-621-3 (2004 ) 321-329. 499
[15] Lindl B. and Schmitz H.G., Cold Start Equipment for Diesel Injection Engines, SAE paper 1999-01-500
1244, 1999. 501
[16] Merskisz J, Bielaczyc P., Pielecha .J, Cold Start Emissions Performance from Direct Injection Diesel 502
Engine, European Automotive Congress, Bratislava 18th-20th June (2001) SAITS 01017. 503
[17] Wang W.G., Lyons D.W., Clark N.N., Gautam M., Norton P.M., Emission from nine heavy trucks 504
fueled by Diesel and Biodiesel blend without engine modification Environ. Sci. technol. 34 (6) (2000) 505
933-939. 506
18
[18] Hideyuki O., Khandoker A.R., Ken-ichi I., and Noboru M., Cycle-to-cycle Transient Characteristics 507
of Diesel Emissions during Starting, SAE paper 1999-01-3495, 1999. 508
[19] Serrano J.R., Climent H., Arnau F.J., Traumat G., Global Analysis of the EGR Circuit in a HSDI 509
Diesel Engine in Transient Operation, SAE paper 2005-01-0699, 2005.510
19
List of captions for tables
Table 1. Diesel Light-Duty engine specifications
Table 2. Correlations for calculation of dry particulate mass (DPM) and total particle mass (PM) from
FSN and THC measurements. = mass concentration (mg/m3), m=specific mass emission (g/kWh),
y=mass fraction in fuel. Subcripts: p= total particle mass, c=dry soot, HC= hydrocarbons.
Table 3. Mean deviations of predictions with respect to experimental data.
List of tables
Table 1
Type of engine HSDI Turbocharged Diesel Engine
Number of cylinders 4 cylinders, in line
Bore 85 mm
Stroke 96 mm
Compression ratio 18
Number of valves 4 per cylinder
Injection system Common-rail
Turbocharger VGT
Charge cooling Air-air
Displacement 2,179 l
Table 2
Author Correlation
Alkidas [3] c=581,4{ln[10/(10·FSN]}1,413
Christian et al. [4] c=1/0,405·4,95·FSN·e0,38FSN
Greeves & Wang [5] p=1,024c+0,505HC
Arcoumanis & Megaritis [6] p=1,038c+0,523HC
Lapuerta et al. [7] mp=mc+KmHC
0,255 0,63 4sulfur ester waterK y y y
This study p=4,78FSN+9,14FSN1,83
+0,28HC
Table 3
Correlation Mean deviation
Alkidas [3] Christian et al. [4] Lapuerta et al. [7]+ Christian et al. [4] Greeves & Wang [5]+ Alkidas [3] Arcoumanis & Megaritis [6]+ Alkidas [3] 0,399
This study
20
List of captions for figures
Figure 1. Experimental set-up.
Figure 2. Correlation between Filter Smoke Number and smoke opacity measurements.
Figure 3. Comparison between total particle mass experiments and predictions of correlations for dry
particulate mass [3][4].
Figure 4. Comparison between experiments and predictions of correlations for total particulate mass.
Figure 5. Comparison of gases and smoke measurements. on different days (UDC cycle for the case
without glow plug).
Figure 6. Alignment of gaseous pollutants and exhaust flow measurements. (UDC cycle for the case
without glow plug).
Figure 7. Water and oil temperatures evolution during the UDC cycle for the cases with and without
glow plug inside the engine cylinder.
Figure 8. Exhaust emissions measurement during the UDC cycle for the cases with and without glow
plug inside the engine cylinder.
Figure 9. Accumulated mass of gaseous and particle emissions during the UDC cycle for the cases with
and without glow plug inside the engine cylinder.
Figure 10. Accumulated fuel consumption during the UDC cycle for the cases with and without glow
plug inside the engine cylinder.
23
Figure 5
0
50
100
150
200
250
300
350
400
0 100 200 300 400 500 600 700 800
t(s)T
HC
(p
pm
)
0
1
2
3
4
5
6
0 100 200 300 400 500 600 700 800
t(s)
CO
(%
)
0
100
200
300
400
500
600
700
0 100 200 300 400 500 600 700 800
t(s)
NO
x (
pp
m)
25-mar
26-mar
27-mar
Day 1
Day 2
Day 3
0
5
10
15
20
25
30
35
40
45
0 100 200 300 400 500 600 700 800
t(s)
Op
acit
y (
%)
26
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
3.00E-02
3.50E-02
4.00E-02
0 100 200 300 400 500 600 700 800
Time (s)
NO
x (
g/s
)NOx emission with glow plug
NOx emission without glow plug
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0 100 200 300 400 500 600 700 800
Time (s)
CO
(g/s
)
CO emission with glow plug
CO emission without glow plug
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0 100 200 300 400 500 600 700 800
Time (s)
TH
C (
g/s
)
THC emission with glow plug
THC emission without glow plug
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
40.000
45.000
0 100 200 300 400 500 600 700 800
Time (s)
Opac
ity (
%)
Opacity with glow plug
Opacity without glow plug
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0 100 200 300 400 500 600 700 800
Time (s)
PM
(mg/s
)
PM with glow plug
PM without glow plug
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700 800
Time (s)
Veh
icle
spee
d (
km
/h)
Figure 9
0
0,5
1
1,5
2
2,5
0 100 200 300 400 500 600 700 800
Time (s)
Acc
um
ula
ted
NO
x (g
)
NOx emission with glow plug
NOx emission without glow plug
0
50
100
150
200
250
300
0 100 200 300 400 500 600 700 800
Time (s)
Acc
um
ula
ted
PM
(g
)
PM emission with glow plug
PM emission without glow plug
0
2
4
6
8
10
12
14
16
0 100 200 300 400 500 600 700 800
Time (s)
Acc
um
ula
ted
CO
(g
)
CO emission with glow plug
CO emission without glow plug
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
0 100 200 300 400 500 600 700 800
Time (s)
Acc
um
ula
ted
TH
C (g
)
THC emission with glow plug
THC emission without glow plug
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