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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.

21

List of figures

Figure 1

Figure 2

22

Figure 3

Figure 4

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 (

%)

24

Figure 6

25

Figure 7

Figure 8

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

27

Figure 10