Correlations of Exhaust Emissions from a Diesel Engine with Diesel ...

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influence of diesel fuel on exhaust emissions.2,3. Emission limits from diesel engines become more stringent, while the fuel quality tends to deteriorate.

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Energy & Fuels 1998, 12, 230-238

Correlations of Exhaust Emissions from a Diesel Engine with Diesel Fuel Properties D. Karonis, E. Lois,* S. Stournas, and F. Zannikos Department of Chemical Engineering, National Technical University of Athens, Iroon Polytechniou 9, Athens 157 80, Greece Received April 10, 1997. Revised Manuscript Received October 10, 1997X

Mathematical expressions are presented in this paper that correlate the exhaust emissions from a single-cylinder diesel engine with some of the most important properties of the fuels used. Exhaust emissions measured were carbon monoxide, unburned hydrocarbons, nitrogen oxides, and particulate matter. The experiments were performed using a matrix of 68 fuels. The cetane number of the fuels covered the range 42-58, the density varied between 0.84 and 0.860 g/mL, and the sulfur content varied from 0.05 to 0.20 wt %. All predictions were based on specific points of the distillation curve, the cetane number, and the density of the fuels. In the case of particulate matter emissions, sulfur content was also employed. Very good predictions were obtained for all the emissions considered. The aromatic content was not used as a predictor variable because it was found to have a strong intercorrelation with the cetane number, density, and the 90% distillation point.

Introduction The diesel engine is the main engine used for freight road transports in Europe and holds a very good share in the United States. Fuel combustion in diesel engines is accomplished with emissions of pollutants. The amount of pollutants emitted from diesel engines is affected by both the engine and the fuel quality. Extended research has been done on the manner by which the engine affects the emitted pollutants.1 During the last years, research has been focused on the influence of diesel fuel on exhaust emissions.2,3 Emission limits from diesel engines become more stringent, while the fuel quality tends to deteriorate. This is because modern refineries produce large amounts of cracked products that find their way in the diesel fuel pool.4 The most studied property of diesel fuel is cetane number. Straight run gas oils have high values of cetane number, while cracked gas oils have low values. Most national specifications have as their low limit of the cetane number about 50. The majority of the studies on the influence of the cetane number on exhaust emissions shows that pollutant emissions decrease as the cetane number increases.5-7 * Author to whom correspondence should be addressed. E-mail: [email protected] X Abstract published in Advance ACS Abstracts, December 15, 1997. (1) Hammerle, R. H.; Ketcher, D. A.; Horrocks, R. W.; Lepperhoff, G.; Hu¨thwohl, G.; Lu¨ers, B. Emissions from Current Diesel Vehicles. SAE Paper 942043; 1994. (2) Reynolds, E. G. The Effect of Fuel Processes on Heavy Duty Automotive Diesel Engine Emissions. SAE Paper 952350; 1995. (3) Ogawa, T.; Araga, T.; Okada, M.; Fujimoto, Y. Fuel Effects on Particulate Emissions from D.I. Engine - Chemical Analysis and Characterization of Diesel Fuel. SAE Paper 952351; 1995. (4) Owen, K.; Coley, T. Automotive Fuels Reference Book, 2nd ed.; SAE: Warrendale, PA, 1995.

Density is also an important property because it controls the amount of fuel that is compressed and burned in the combustion chamber. The higher the amount of fuel sprayed in the combustion chamber, the higher the output of partially oxidized products emitted. The use of fuels with higher density than that of the homologated fuel results in higher emissions of particulate matter and smoke.8,9 On the other hand, the use of low-density fuels leads to less output power from the engine.10-12 The role of the aromatic content of the fuel on exhaust emissions is not very clear. Some investigators report higher particulate emissions with use of fuels with high aromatic content.13,14 Other investigators report that the aromatic content influence can be very well described by the variance of both cetane number and (5) Weidmann, K.; Menrad, H.; Reders, K.; Hutcheson, R. C. Diesel Fuel Quality Effects on Exhaust Emissions. SAE Paper 881649; 1988. (6) McMillan, M.; Halsall, R. Fuel Effects on Combustion and Emissions in a Direct Injection Diesel Engine. SAE Paper 881650; 1988. (7) McCarthy, C. I.; Slodowske, W. J.; Sienicki, E. J.; Jass, R. E. Diesel Fuel Property Effects on Exhaust Emissions from a Heavy Duty Diesel Engine that Meets 1994 Emission Requirements. SAE Paper 922267; 1992. (8) Fanick, E. R.; Whitney, K. A. Particulate Characterization Using Five Fuels. SAE Paper 961089; 1996. (9) Singal, S. K.; Pundir, B. P. Diesel Fuel Quality and Particulate Emissions: An Overview. SAE Paper 961185; 1996. (10) Betts, W. E.; Fløysand, S. A° .; Kvinge, F. The Influence of Diesel Fuel Properties on Particulate Emissions in European Cars. SAE Paper 922190; 1992. (11) Puttick, J. R.; Dwyer, G. W. Fuel Effects on Road Transport Engines - Emissions and Cold Starting, Fuels for Automotive and Industrial Diesel Engines; IMechE: London, 1990. (12) van Beckhoven, L. D. Effects of Fuel Properties on Diesel Engine Emissions - A Review of Information Available to EEC-MVEG Group. SAE Paper 910608; 1991. (13) Miyamoto, N.; Ogawa, H.; Shibuya, M. Distinguishing the Effects of Aromatic Content and Ignitability of Fuels in Diesel Combustion and Emissions. SAE Paper 912355; 1991.

S0887-0624(97)00058-3 CCC: $15.00 © 1998 American Chemical Society Published on Web 02/14/1998

Correlations of Exhaust Emissions with Fuel Properties

Energy & Fuels, Vol. 12, No. 2, 1998 231

Table 1. Properties of the Base Fuels fuel code

cetane number

cetane index

IBP (°C)

D10 (°C)

D50 (°C)

D90 (°C)

FBP (°C)

density (g/mL, 15 °C)

ν40 (cSt)

ν100 (cSt)

pour point (°C)

aniline point (°C)

aromatic content (vol %)

total sulfur (wt %)

BF1 BF2 BF3 BF4

42.0 58.1 52.2 58.2

42.9 57.2 51.6 57.6

198 180 208 188

227 260 235 249

265 300 263 285

313 353 327 313

344 369 350 329

0.8610 0.8490 0.8412 0.8411

2.77 4.55 2.90 3.36

1.12 1.51 1.18 1.33

-16 2 -20 -9

50.2 74.5 68.9 72.2

45.9 22.6 27.6 23.1

0.02 0.03 0.05 0.19

Figure 1. Carbon monoxide emissions vs cetane number.

density.15,16 The most recent research is focused on the influence of di- and tri-aromatics on exhaust emissions, rather than the total aromatics.17-20 The distillation curve is a measure of fuel volatility. Back-end volatility is in some cases associated with particulate emissions.21,22 However, it should be kept in mind that paraffinic hydrocarbons with high cetane (14) Miyamoto, N.; Ogawa, H.; Shibuya, M.; Suda, T. Description of Diesel Emissions by Individual Fuel Properties. SAE Paper 922221; 1992. (15) Diesel Fuel. CONCAWE Rev. 1992, 1 (1), 10. (16) Virk, K. S.; Lachowicz, D. R. Prepr. Pap.sAm. Chem. Soc., Div. Pet. Chem. 1992, 37, 701-709. (17) Bertoli, C.; Del Giacomo, N.; Iorio, B.; Prati, V. The Influence of Fuel Composition on Particulate Emissions of DI Diesel Engines. SAE Paper 932733; 1993. (18) Mitchell, K.; Steere, D. E.; Taylor, J. A.; Manicom, B.; Fischer, J. E.; Sienicki, E. J.; Chiu, C.; Williams, P. Impact of Diesel Fuel Aromatics on Particulate, PAH and Nitro-PAH Emissions. SAE Paper 942053; 1994. (19) Rainbow, L. J.; Le Jeune, A.; Lang, G.; McDonald, C. R. European Program on Emissions, Fuels and Engine Technologies (EPEFE) - Gasoline and Diesel Test Fuels Blending and Analytical Data. SAE Paper 961066; 1996. (20) Morgan, T. D. B.; Belot, G.; Beckwith, P.; Malpas, R. E.; Scha¨fer, H. V. European Program on Emissions, Fuels and Engine Technologies (EPEFE) - Statistical Design and Analysis Techniques. SAE Paper 961070; 1996. (21) Bergin, S. P. The Influence of Fuel Properties and Engine Load Upon the Carbon and Hydrocarbon Fractions of Particulate Emissions from a Light-Duty Diesel Engine. SAE Paper 831736; 1983.

Figure 2. number.

Unburned hydrocarbons emissions vs cetane

numbers (C18 to C22) have high boiling points, and their exclusion from the fuel will result in a decrease in the cetane number. The world specifications trend on sulfur content is to minimize it. The European Union has specified the limit for sulfur content to 0.05 wt % since October 1996. Sulfur content results in sulfates that are absorbed on soot particles and increase the particulate matter emitted from diesel engines.23,24 This work is an effort to correlate the exhaust emissions from a single-cylinder diesel engine with diesel fuel properties. The objective of the work was to obtain correlations of the exhaust emissions from a single-cylinder diesel engine with the minimum number of the required fuel parameters. The parameters used for the prediction of exhaust emissions were the cetane number, density, specific points of the distillation curve, and the sulfur content. (22) Gaskill, G. P. The Influence of Diesel Fuel Back-End Volatility on Emissions. CEN/TC19/WG24; 1990. (23) Baranescu, R. A. Influence of Fuel Sulfur on Diesel Particulate Emissions. SAE Paper 881174; 1988. (24) Richards, R. R.; Sibley, J. E. Diesel Engine Emissions Control for the 1990s. SAE Paper 880346; 1988.

232 Energy & Fuels, Vol. 12, No. 2, 1998

Karonis et al. Table 2. Fuel Properties

fuel code

cetane number

cetane index

IBP (°C)

D10 (°C)

D50 (°C)

D90 (°C)

FBP (°C)

density (g/mL, 15 °C)

ν40 (cSt)

ν100 (cSt)

pour point (°C)

aniline point (°C)

aromatic content (vol %)

total sulfur (wt %)

BF1 BF1-10 BF1-20 BF2 BF2-10 BF2-20 BF3 BF3-10 BF3-20 BF4 I1-05 I2-05 I3-05 I4-05 I5-05 I6-05 I7-05 I1-10 I2-10 I3-10 I4-10 I5-10 I6-10 I7-10 I1-20 I2-20 I3-20 I4-20 I5-20 I6-20 I7-20 II1-05 II2-05 II3-05 II1-10 II2-10 II3-10 II1-20 II2-20 II3-20 III1-05 III2-05 III3-05 III1-10 III2-10 III3-10 III1-20 III2-20 III3-20 IV1 IV2 IV3 IV4 IV5 IV6 IV7 V1 V2 V3 IO1 IO2 IO3 IO4 IO5 IO6 IO7 IO8 IO9

42.0 42.0 42.0 58.1 58.1 58.1 52.2 52.2 52.2 58.2 44.2 45.7 49.0 51.2 52.2 54.2 56.0 44.2 45.7 49.0 51.2 52.2 54.2 56.0 44.2 45.7 49.0 51.2 52.2 54.2 56.0 45.6 47.6 49.8 45.6 47.6 49.8 45.6 47.6 49.8 53.8 55.2 56.7 53.8 55.2 56.7 53.8 55.2 56.7 44.4 46.1 48.6 50.2 52.3 54.0 55.4 58.1 58.1 58.1 45.7 51.2 52.2 54.2 48.0 50.0 53.5 56.0 57.0

42.9 42.9 42.9 57.2 57.2 57.2 51.6 51.6 51.6 57.6 44.7 46.2 48.1 49.4 50.9 53.2 54.8 44.7 46.2 48.1 49.4 50.9 53.2 54.8 44.7 46.2 48.1 49.4 50.9 53.2 54.8 45.7 47.5 49.4 45.7 47.5 49.4 45.7 47.5 49.4 53.0 54.2 55.6 53.0 54.2 55.6 53.0 54.2 55.6 44.8 46.5 48.5 49.7 51.4 53.1 54.7 57.2 57.1 56.9 42.9 42.9 42.9 42.9 46.2 46.2 46.2 46.2 46.2

198 198 198 180 180 180 208 208 208 188 196 194 194 192 190 188 186 196 194 194 192 190 188 186 196 194 194 192 190 188 186 202 206 203 202 206 203 202 206 203 203 195 186 203 195 186 203 195 186 198 197 196 195 195 193 191 183 184 185 198 198 198 198 194 194 194 194 194

227 227 227 260 260 260 235 235 235 249 229 231 235 237 239 247 251 229 231 235 237 239 247 251 229 231 235 237 239 247 251 230 231 232 230 231 232 230 231 232 239 243 248 239 243 248 239 243 248 229 231 234 235 236 239 244 258 255 252 227 227 227 227 231 231 231 231 231

265 265 265 300 300 300 263 263 263 285 268 272 278 282 287 292 296 268 272 278 282 287 292 296 268 272 278 282 287 292 296 266 265 264 266 265 264 266 265 264 273 282 293 273 282 293 273 282 293 268 272 276 278 281 283 284 289 293 290 265 265 265 265 272 272 272 272 272

313 313 313 353 353 353 327 327 327 313 323 329 338 340 342 348 349 323 329 338 340 342 348 349 323 329 338 340 342 348 349 320 321 323 320 321 323 320 321 323 337 345 351 337 345 351 337 345 351 313 314 314 314 314 314 314 346 335 324 313 313 313 313 329 329 329 329 329

344 344 344 369 369 369 350 350 350 329 353 360 363 366 368 370 370 353 360 363 366 368 370 370 353 360 363 366 368 370 370 345 347 347 345 347 347 345 347 347 358 361 367 358 361 367 358 361 367 341 340 338 336 334 332 331 364 356 350 344 344 344 344 360 360 360 360 360

0.8610 0.8610 0.8610 0.8490 0.8490 0.8490 0.8412 0.8412 0.8412 0.8411 0.8595 0.8580 0.8565 0.8550 0.8535 0.8520 0.8505 0.8595 0.8580 0.8565 0.8550 0.8535 0.8520 0.8505 0.8595 0.8580 0.8565 0.8550 0.8535 0.8520 0.8505 0.8561 0.8511 0.8462 0.8561 0.8511 0.8462 0.8561 0.8511 0.8462 0.8432 0.8451 0.8471 0.8432 0.8451 0.8471 0.8432 0.8451 0.8471 0.8578 0.8550 0.8518 0.8500 0.8475 0.8451 0.8431 0.8470 0.8451 0.8431 0.8610 0.8610 0.8610 0.8610 0.8580 0.8580 0.8580 0.8580 0.8580

2.77 2.77 2.77 4.55 4.55 4.55 2.90 2.90 2.90 3.36 2.97 3.11 3.32 3.56 3.76 3.98 4.26 2.97 3.11 3.32 3.56 3.76 3.98 4.26 2.97 3.11 3.32 3.56 3.76 3.98 4.26 2.80 2.83 2.87 2.80 2.83 2.87 2.80 2.83 2.87 3.22 3.59 4.23 3.22 3.59 4.23 3.22 3.59 4.23 2.85 2.93 3.02 3.08 3.15 3.23 3.29 4.19 3.87 3.60 2.77 2.77 2.77 2.77 3.11 3.11 3.11 3.11 3.11

1.12 1.12 1.12 1.51 1.51 1.51 1.18 1.18 1.18 1.33 1.16 1.22 1.26 1.32 1.36 1.40 1.45 1.16 1.22 1.26 1.32 1.36 1.40 1.45 1.16 1.22 1.26 1.32 1.36 1.40 1.45 1.13 1.15 1.16 1.13 1.15 1.16 1.13 1.15 1.16 1.25 1.33 1.41 1.25 1.33 1.41 1.25 1.33 1.41 1.15 1.18 1.21 1.23 1.26 1.28 1.31 1.46 1.42 1.37 1.12 1.12 1.12 1.12 1.22 1.22 1.22 1.22 1.22

-16 -16 -16 2 2 2 -20 -20 -20 -9 -14 -12 -10 -8 -5 -3 -1 -14 -12 -10 -8 -5 -3 -1 -14 -12 -10 -8 -5 -3 -1 -17 -18 -19 -17 -18 -19 -17 -18 -19 -13 -7 -2 -13 -7 -2 -13 -7 -2 -15 -14 -13 -12 -11 -10 -10 0 -3 -6 -16 -16 -16 -16 -12 -12 -12 -12 -12

50.2 50.2 50.2 74.5 74.5 74.5 68.9 68.9 68.9 72.2 53.4 56.4 60.0 63.0 66.2 69.0 71.6 53.4 56.4 60.0 63.0 66.2 69.0 71.6 53.4 56.4 60.0 63.0 66.2 69.0 71.6 55.1 59.7 64.3 55.1 59.7 64.3 55.1 59.7 64.3 70.2 71.8 73.1 70.2 71.8 73.1 70.2 71.8 73.1 53.8 56.9 60.6 62.7 65.3 67.9 70.2 73.9 73.3 72.8 50.2 50.2 50.2 50.2 56.4 56.4 56.4 56.4 56.4

45.9 45.9 45.9 22.6 22.6 22.6 27.6 27.6 27.6 23.1 43.1 40.0 37.2 34.2 31.4 28.5 25.6 43.1 40.0 37.2 34.2 31.4 28.5 25.6 43.1 40.0 37.2 34.2 31.4 28.5 25.6 41.2 36.6 32.3 41.2 36.6 32.3 41.2 36.6 32.3 26.4 25.1 23.9 26.4 25.1 23.9 26.4 25.1 23.9 42.3 39.1 35.5 33.1 30.5 27.7 25.4 22.7 22.9 23.0 45.9 45.9 45.9 45.9 40.0 40.0 40.0 40.0 40.0

0.02 0.10 0.20 0.03 0.10 0.20 0.05 0.10 0.20 0.19 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.03 0.03 0.04 0.10 0.10 0.10 0.20 0.20 0.20 0.04 0.04 0.03 0.10 0.10 0.10 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.19 0.19 0.19 0.20 0.20 0.20 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02

Experimental Section Test Fuels. Four gas oils with different properties were used as base fuels in this course of experiments. Their cetane number was in the range 42-58. From these base fuels, 28 blends were prepared, covering a large spectrum of properties that reflect both current and future trends. Three of the four base fuels have very low sulfur content (less than 0.05 wt %), satisfying the current stringent specification of the European

Union. To examine the influence of sulfur content on exhaust (especially particulate) emissions, bi-tert-butyl sulfide was added to low-sulfur fuels. From the addition of the sulfide, 32 more fuel blends were prepared with sulfur content 0.10 and 0.20 wt %. Cetane number is referred to as the most important fuel property affecting emissions. For this reason, isooctyl nitrate, a commercial cetane improver, was added to the two low cetane number fuels. The total number of fuels that were used

Correlations of Exhaust Emissions with Fuel Properties

Energy & Fuels, Vol. 12, No. 2, 1998 233

Table 3. Fuel Blends Composition fuel code

composition

BF1 BF1-10 BF1-20 BF2 BF2-10 BF2-20 BF3 BF3-10 BF3-20 BF4 I1-05 I2-05 I3-05 I4-05 I5-05 I6-05 I7-05 I1-10 I2-10 I3-10 I4-10 I5-10 I6-10 I7-10 I1-20 I2-20 I3-20 I4-20 I5-20 I6-20 I7-20 II1-05 II2-05 II3-05

100% BF1 100% BF1 100% BF1 100% BF2 100% BF2 100% BF2 100% BF3 100% BF3 100% BF3 100% BF4 87.5% BF1 + 12.5% BF2 75.0% BF1 + 25.0% BF2 62.5% BF1 + 37.5% BF2 50.0% BF1 + 50.0% BF2 37.5% BF1 + 62.5% BF2 75.0% BF1 + 25.0% BF2 12.5% BF1 + 87.5% BF2 87.5% BF1 + 12.5% BF2 75.0% BF1 + 25.0% BF2 62.5% BF1 + 37.5% BF2 50.0% BF1 + 50.0% BF2 37.5% BF1 + 62.5% BF2 75.0% BF1 + 25.0% BF2 12.5% BF1 + 87.5% BF2 87.5% BF1 + 12.5% BF2 75.0% BF1 + 25.0% BF2 62.5% BF1 + 37.5% BF2 50.0% BF1 + 50.0% BF2 37.5% BF1 + 62.5% BF2 75.0% BF1 + 25.0% BF2 12.5% BF1 + 87.5% BF2 75.0% BF1 + 25.0% BF3 50.0% BF1 + 50.0% BF3 25.0% BF1 + 75.0% BF3

bi-tert-butyl sulfide content (%)

isooctyl nitrate content (%)

0.22 0.50 0.20 0.48 0.14 0.42

0.22 0.22 0.22 0.22 0.20 0.20 0.20 0.50 0.50 0.50 0.50 0.48 0.48 0.48

Figure 3. Nitrogen oxides emissions vs cetane number.

fuel code

composition

II1-10 II2-10 II3-10 II1-20 II2-20 II3-20 III1-05 III2-05 III3-05 III1-10 III2-10 III3-10 III1-20 III2-20 III3-20 IV1 IV2 IV3 IV4 IV5 IV6 IV7 V1 V2 V3 IO1 IO2 IO3 IO4 IO5 IO6 IO7 IO8 IO9

75.0% BF1 + 25.0% BF3 50.0% BF1 + 50.0% BF3 25.0% BF1 + 75.0% BF3 75.0% BF1 + 25.0% BF3 50.0% BF1 + 50.0% BF3 25.0% BF1 + 75.0% BF3 25.0% BF2 + 75.0% BF3 50.0% BF2 + 50.0% BF3 75.0% BF2 + 25.0% BF3 25.0% BF2 + 75.0% BF3 50.0% BF2 + 50.0% BF3 75.0% BF2 + 25.0% BF3 25.0% BF2 + 75.0% BF3 50.0% BF2 + 50.0% BF3 75.0% BF2 + 25.0% BF3 84.0% BF1 + 16.0% BF4 70.0% BF1 + 30.0% BF4 53.8%BF1 + 46.2% BF4 44.7% BF1 + 55.3% BF4 32.2% BF1 + 67.8% BF4 20.0% BF1 + 80.0% BF4 10.0% BF1 + 90.0% BF4 75.0% BF2 + 25.0% BF4 50.0% BF2 + 50.0% BF4 25.0% BF2 + 75.0% BF4 100% BF1 100% BF1 100% BF1 100% BF1 75.0% BF1 + 25.0% BF2 75.0% BF1 + 25.0% BF2 75.0% BF1 + 25.0% BF2 75.0% BF1 + 25.0% BF2 75.0% BF1 + 25.0% BF2

bi-tert-butyl sulfide content (%)

isooctyl nitrate content (%)

0.20 0.17 0.17 0.48 0.45 0.45

0.14 0.17 0.20 0.45 0.48 0.50 0.42 0.36 0.28 0.25 0.20 0.11 0.08 0.36 0.25 0.14 0.09 0.24 0.54 0.65 0.04 0.10 0.28 0.50 0.60

Figure 4. Particulate matter emissions vs cetane number.

234 Energy & Fuels, Vol. 12, No. 2, 1998

Figure 5. Carbon monoxide emissions vs density.

Figure 6. Unburned hydrocarbons emissions vs density. (including the base fuels) was 68. The properties of the base fuels are given in Table 1. The properties of the 64 blends are given in Table 2. Table 3 gives details for the composition

Karonis et al.

Figure 7. Nitrogen oxides emissions vs density.

Figure 8. Particulate matter emissions vs density. of the fuel blends. All testing and measurements were done according to the appropriate ASTM procedures. Test Procedures. The engine employed for the measurements was a Petter AV1-LAB single-cylinder diesel engine.

Correlations of Exhaust Emissions with Fuel Properties

Figure 9. Aromatic content vs cetane number.

Energy & Fuels, Vol. 12, No. 2, 1998 235

Figure 11. Estimated vs measured aromatic content.

Figure 10. Aromatic content vs density. The nominal power of the engine was 3.7 kW at 1500 rpm. The engine’s speed was governed at 1500 rpm for all engine loads. The test rig comprised an electrical dynamometer and heat exchangers for lubricating oil and cooling fluid (mixture of water and glycol).

Figure 12. Estimated vs measured carbon monoxide emissions. Carbon monoxide (CO), unburned hydrocarbons (HC), carbon dioxide (CO2), and oxygen were measured with a Horiba instrument, type MEXA 574-GE. For the measurement of

236 Energy & Fuels, Vol. 12, No. 2, 1998

Karonis et al.

Table 4. Statistical Parameters of Estimating Equations

a

parameter

eq 1

eq 2

eq 3

eq 4

eq 5

a b c d e s R2 R2adj

-61.377E+1a

-23.597E+0 -20.110E-2 45.030E+0

-31.400E-1 -39.657E-3 60.670E-2 35.182E-4

-108.109E-3 183.862E-1 80.400E-4

3.300E-1 9.260E-1 9.210E-1

8.600E-2 8.390E-1 8.310E-1

2.460E-1 8.330E-1 8.310E-1

-79.778E-1 -10.373E-3 106.487E-1 383.949E-2 16.163E-4 3.300E-2 9.870E-1 9.860E-1

-32.335E-2 85.073E+1 -18.464E-2 1.537E+0 9.630E-1 9.610E-1

Read as -61.377 × 10+1.

nitrogen oxides (NO, NOx) a Signal 4100 instrument was employed. Exhaust gas was carried to the instruments through heated lines. The outputs of these two instruments were fed through an A/D converter to a computer, where they were recorded at 1 s intervals. Particulate matter emissions were measured using a Joy Manufacturing Co. system that consisted of a suction pump, a gas meter for the measurement of the volume of the exhaust gas, and a filter of glass fibers on which particulate matter was collected. Each fuel was tested at five different engine loads (2, 25, 50, 75, and 100% of the engine’s nominal power). Exhaust emissions are given as weighted averages of the measurement at each load in terms of g/kW h, according to SAE J1003 Recommended Practice.25

Results and Discussion Influence of Fuel Properties on Exhaust Emissions. As mentioned above, the cetane number and the density are the most significant properties of diesel fuels affecting exhaust emissions from diesel engines. Figure 1 gives graphically the relationship of carbon monoxide emissions and cetane number. It is clear that the higher the cetane number, the lower the carbon monoxide emissions. In Figure 2 is presented the relationship between unburned hydrocarbons emissions and cetane number. Fuels with high cetane number have low unburned hydrocarbons emissions. The influence of cetane number on nitrogen oxides emissions is given graphically in Figure 3. As it can be seen, use of fuels with high cetane number results in lower nitrogen oxides emissions. In the case of particulate matter emissions, the results are given graphically in Figure 4. Fuels with high cetane number seem to have lower particulate matter emissions. From Figure 4, it is obvious that the sulfur content of the fuel strongly influences the particulate matter emissions. Figure 5 gives in graphical form the relation of carbon monoxide emissions and the density of the fuels. It can be seen that fuels with low density have low carbon monoxide emissions. Figure 6 shows how the density affects the unburned hydrocarbon emissions. Again, fuels with low density have low unburned hydrocarbons emissions. The relationship between density and nitrogen oxides emissions is depicted in Figure 7. The lower the density of the fuel, the lower the nitogen oxides emissions. In Figure 8, the influence of the density on particulate matter emissions is presented in graphical form. It is obvious that fuels with low density have low emissions of particulate matter. It is noted that, in all the previous figures, the scatter in all the cases where the density is the independent (25) Diesel Engine Emission Measurement Procedure, SAE Handbook; SAE J1003; SAE: Warrendale, PA, 1992; Vol. 3

variable is higher than that in the cases where the independent variable is the cetane number. This means that the cetane number is a more important property in affecting exhaust emissions than the density. Statistical Analysis. The data of the exhaust emissions and fuel properties were analyzed using standard statistical techniques. For each property, the parameters considered were the standard deviation s, the correlation coefficient R2, and the adjusted correlation coefficient R2adj, which gives a more accurate behavior of the model used. Each expression was tested through the t-test and probability number p to ensure that only significant terms were used in the mathematical expressions.26 Correlation between Fuel Properties. Statistical analysis for the correlation between various fuel properties showed that the aromatic content has a strong intercorrelation with the cetane number, density, and 90% recovery point. Figure 9 depicts the relationship between the cetane number and the aromatic content for the fuels that were used. In Figure 10 is presented the relationship between the density and the aromatic content of the fuels in graphical form. The proposed equation is

AROM ) a + bCN + cDENS + dD90

(1)

The values of the constants are given in Table 4. The equation is depicted in Figure 11. From these results it becomes evident that the aromatic content is not a significant parameter for the estimation of exhaust emissions and is well covered with the other fuel properties. Estimation of Carbon Monoxide Emissions. Statistical analysis for the estimation of carbon monoxide emissions from fuel parameters showed that carbon monoxide is well correlated to the cetane number and density of the fuel. The proposed equation is

CO ) a + bCN + cDENS

(2)

Estimation parameters are given in Table 4. The results are plotted in Figure 12. It is clear from Figure 12 that the correlation is very good and uses only two properties as predictor variables. Estimation of Unburned Hydrocarbon Emissions. Unburned hydrocarbons use three parameters as predictor variables: cetane number, density, and 90% recovery point. The proposed equation is

HC ) a + bCN + cDENS + dD90

(3)

The correlation coefficient is lower than that of carbon monoxide emissions but is quite good. The results are (26) Ryan, B.; Joiner, B.; Ryan, T. Minitab Handbook, 2nd ed.; PWS-KENT Publishing Company: Boston, 1992.

Correlations of Exhaust Emissions with Fuel Properties

Figure 13. Estimated vs measured unburned hydrocarbons emissions.

Energy & Fuels, Vol. 12, No. 2, 1998 237

Figure 14. Estimated vs measured nitrogen oxides emissions.

depicted in Figure 13, and estimation parameters are given in Table 4. Estimation of Nitrogen Oxides Emissions. Nitrogen oxides emissions are well known to correlate better with engine parameters rather than fuel properties. For the prediction of nitrogen oxides emissions, the same parameters as in the case of unburned hydrocarbons are used, i.e., cetane number, density, and 90% recovery point. The proposed equation is

NOx ) aCN + bDENS + cD90

(4)

Estimation parameters are given in Table 4, while a graphical representation of the results is given in Figure 14. Estimation of Particulate Matter Emissions. Particulate matter is considered the “Achilles heel” of the diesel engine. In this case, the prediction of particulate matter emissions uses more fuel properties as predictor variables. These are the cetane number, density, sulfur content, and the final boiling point. The proposed equation is

PM ) a + bCN + cDENS + dS + eFBP

(5)

The correlation coefficient of this equation is almost excellent. Values of constants of the predictor variables are given in Table 4. Graphical representation is given in Figure 15. It is worth mentioning here that the above results apply only to the specific engine used in this series of experiments, using the fuel matrix presented in Tables 1-3. Conclusions Mathematical expressions that predict exhaust emissions from a single-cylinder diesel Petter engine have

Figure 15. Estimated vs measured particulate matter emissions.

been experimentally determined. These results were obtained by testing a total of 68 fuels. Very good

238 Energy & Fuels, Vol. 12, No. 2, 1998

predictions were obtained for carbon monoxide, unburned hydrocarbons, nitrogen oxides, and particulate matter emissions. From this study, it is concluded that the most significant fuel parameters are the cetane number, density, 90% recovery point, and the final boiling point of the distillation curve. In the case of particulate matter, sulfur content is a very important property. On the other hand, aromatic content appeared to be a nonsignificant property since it correlates well with the cetane number, density, and the 90% recovery point of the distillation curve. It was also noted that fuels with a higher cetane number due to the addition of cetane improver gave results similar to the fuels with similar cetane number but without cetane improver. Glossary List of Symbols a, b, c, d, e AROM

constants aromatic content of the fuel (vol %)

Karonis et al. CN CO DENS D10 D50 D90 FBP HC NOx p PM R2 R2adj S s

cetane number carbon monoxide emissions (g/kW h) fuel density (g/mL at 15 °C) distillation temperature for the 10 vol % of the fuel (°C) distillation temperature for the 50 vol % of the fuel (°C) distillation temperature for the 90 vol % of the fuel (°C) final boiling point of the fuel (°C) unburned hydrocarbons emission (g/kW h) nitrogen oxides emissions (g/kW h) probability, given by the t-test particulate matter emissions (g/kW h) correlation coefficient adjusted correlation coefficient sulfur content of the fuel (wt %) standard deviation

Greek Letters ν40 ν100

kinematic viscosity (cSt at 40 °C) kinematic viscosity (cSt at 100 °C) EF9700588

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