Environ. Sci. Technol. 1994, 28, 965-972
A Multivariate Statistical Analysis of Fuel-Related Polycyclic Aromatic Hydrocarbon Emissions from Heavy-Duty Diesel Vehicles Roger Westerholm’ and Hang Li Department of Analytical Chemistry, Arrhenius Laboratory, Stockholm University,
The fuel-dependent emissions of polycyclic aromatic hydrocarbons (PAH) were studied in diluted exhaust from two heavy-duty diesel vehicles during transient driving conditions. Principal component analysis (PCA) was used to investigate the relationship between fuel parameters and PAH contents in fuels. The PCA model shows that certain fuel parameters are related to PAH contents in diesel fuels. Linear regression analysis, PCA, and partial least-squares regression to latent structures (PLS) were used to study the correlation of PAH in fuels and PAH in exhaust emissions. The statisticalmethods used support the fact that there is a relationship between PAH contents in the diesel fuel and PAH contents emitted in the exhaust emissions. The PLS model resulted in correlation coefficients of r = 0.97 and r = 0.93 for vehicles 1 and 2, respectively. The PAH emission emitted in the exhaust consists of uncombusted through fuel input PAH and PAH formed in the combustion process. This investigation shows that it is possible to reduce PAH emissions in exhaust originating from uncombusted fuel PAH by using diesel fuels with PAH contents less than 4 mg/L. Introduction
Exhaust emissions from vehicles are important contributors to air pollution in urban areas. Exhaust emissions from vehicles comprise regulated and unregulated pollutants. Emissions of carbon monoxide (CO), unburned fuel hydrocarbons (HC), nitrogen oxides (NO,), and particulate are regulated by law ( I ) . Polycyclic aromatic hydrocarbons (PAH) are included in the great number of compounds present in the group of unregulated pollutants emitted from vehicles. Some of these compounds in the group of PAH are mutagenic in the Ames test and even in some cases cause cancer in animals after skin painting experiments (2, 3 ) . Because of this, it is important to limit the emissions of PAH from vehicles especially in densely populated high-trafficked urban areas. Important factors affecting the emissions of PAH from vehicles are the following: engine exhaust aftertreatment concept, i.e., catalyst contra noncatalyst; ambient temperature ( 4 ) ; driving conditions (5); and selection of fuel and fuel components (6-11). However, in this present study, an investigation was carried out of a linear regression analysis model and two multivariate analysis models, i.e., principal component analysis (PCA) and partial least-squares regression projection to latent structures (PLS), in order to examine the correlation between PAH in diesel fuels and corresponding PAH in exhaust emissions. The main goals of the present study are (i) to determine the correlation between fuel parameters and PAH contents in diesel fuel, (ii) to determine the correlation between PAH contents in diesel fuel and PAH contents in exhaust emissions, and (iii) to classify diesel fuels. In Sweden, PAH content in diesel fuel is regulated in the most rigorous environmental quality class by law (12). The regulation 0013-936X/94/0928-0965$04.50/0
0 1994 American Chemical Society
S-106 9 1 Stockholm,
Sweden
Table 1. Vehicle Data and Fuel Consumption vehicle data
vehicle 1
vehicle 2
vehicle engine type deplacement vol (L) maximum effect (kW) service w t (kg) max w t (kg) fuel consumption (gikm) D1 D2 D4 D5 D6 D7 D8 D9
Scania 113 (bus) DSC 1104 191 (1800 rpm) 10480 15800
Volvo FL 10 (truck) T D 101 F 9.6 229 (2050 rpm) 8570 19000
343 344 352 372 375 364 368 372
356 356 361 355 359 357 360 352
11
of Swedish diesel fuels into environmental classes has been in force since the first of January 1992. Experimental Section
Vehicles. Two heavy-duty vehicles, a bus and a truck, denoted vehicle 1 (Vl) and vehicle 2 (V2), respectively, have been used in this investigation. Vehicle data and fuel consumption are presented in Table 1. It must be pointed out that the vehicles should not be compared to each other, because the aim of this present investigation was not used to evaluate the technical development of vehicles but to investigate fuel PAH-related emissions. Prior to testing, oil filters and engine lubricant oil were changed. The lubricating oil used was a quality synthetic lubricating oil (Mobil Delvac 1) chosen to minimize the contribution from engine oil PAH to the emission (13).All tests were carried out with the engines at working temperature. Fuels. Eight diesel fuels studied (denoted D1, D2, D4, D5, D6, D7, D8, and D9, respectively) have been analyzed for fuel standard properties a t the same laboratory a t a refinery. Of the eight fuels, D1, D2, and D4 are from the same base fuel; D1 has the lowest and D4 has the highest density of these fuels. D5 is a blend of kerosenes. D6 was of a Swedish summer commercial diesel fuel quality. D7 and D8 are the same fuel except that 2000 ppm of an ignition improver, ethyl hexyl nitrate (EHN), was added to D7 in order to get a fuel, D8, with increased cetane number, Table 2. Lastly, D9 is a blend of cracked gas oils with a low sulfur content. Fuel parameters and PAH contents in fuels are shown in Table 2, which shows the same fuels used in a comprehensive diesel fuel investigation (10). The present study and results originate from the same investigation but have not been published previously. Driving Conditions. The vehicles were operated on a chassis dynamometer in the transient driving cycle Stochastischer Fahrzyklus fur Stadtlinien Omnibusse (the “bus cycle”), which was developed a t the University of Braunschweig (Germany). It simulates public transportation in city traffic driving operations. It has a duration Environ. Sci. Technol., Vol. 28, No. 5, 1994
965
Table 2. Fuel Parameters and Polycyclic Aromatic Hydrocarbons Contents variable F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F270
fuel parameters
(E")
PI P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22D a
D1
D2
cetane nos. 52.8 cetane index (ASTM 0976-80) 52.8 density (giL), 15 O C 811.7 2.11 viscosity (KV), 40 "C 220 distillation initial boiling point ("C) 226 5% 10% 228 236 50 % 251 90 % 254 95 % 261 final boiling point ("C) total distillation ( % ) 98.7 cold filter plugging point ("C) -40 -34 cloud point ("C) flash point ("C) 87 35.1 energy (MJiL) total aromatics (vol '%) 1.8 monoaromatics (vol % ) 1.8 0.05 diaromatics (vol %) 0.05 triaromatics (vol % ) 0.01 sulfur (wt '% ) water (wt, ppm) 15 2.7 aromatics (vol % FIA) 1.4 olefins (vol % FIA) 53.6 naphthenes (wt %) 45.6 paraffins (wt % ) ethylhexyl nitrate wt
D4
D6
D7
D8
47.0 48.9 831.3 2.26 190
48.3 48.3 836.8 2.47 180
44.7 43.6 808.3 1.41 180
55.7 42.7 808.7 1.44 176
52.8 50.6 813.2 1.96 175
230 231 239 252 256 260 98.2 -39 -35 87 35.4 16.6 16.2 0.4 0.05 0.01 20 14.7 2 38.8 45.5
230 233 241 252 256 261 98.6 -39 -34 92 35.7 23 18.1 4.9 0.05 0.29 70 22.5 2.2 29.6 43.8
214 220 248 289 304 323 98.8 -32 -24 75 35.7 25.1 21.1 3.8 0.2 0.02 50 26 1.6 27.2 47.6
199 205 253 329 347 364 98.5 -22 -8 71 35.9 26.1 20.2 4.8 1.1 0.16 70 27.7 1 25.9 46.9
188 190 206 245 275 300 98.1 -40 -40 64 35 20 17.2 2.7 0.1 0.02 60 19.8 0.9 32.9 48.5
185 187 204 243 271 299 98.2 -40 -40 64 35.1 20.5 17.2 2.7 0.6 0.01 73 19.4 0.2 32.9 47.7 0.2
202 205 231 282 291 301 98.5 -40 -40 75 35.1 17.3 14.5 2.2 0.6 0.01 58 16 0.7 25.5 58.1
70)
phenanthrene anthracene 3-methylphenanthrene 2-methylanthracene 48~9-methylphenanthrene 1-methylphenanthrene fluoranthrene pyrene 1-methyl-7-isopropylphenanthrene benzo [a]fluorene 2-methylpyrene 1-methylpyrene benzo[ghi] fluoranthrene cyclopenta[cdlpyrene benz[alanthracene chrysene/triphenylene benzo[ b&klfluoranthene benzo[el pyrene indeno[l,2,3-cdlpyrene picene benzo[ghiIperylene sum of PAH (21)
1.7 X 2.6 X 1.8 X 1.8 X 1.2 X 1.0 X 1.4 X 1.6 X 1.3 X 5.7 x 4.2 X 5.6 X 3.0 X 5.7 X 3.5 X 4.3 x 5.1 X 4.8 X 5.6 X 3.1 x 8.0 X 1.4
D9
47.2 46.8 832.0 2.09 221
Polycyclic Aromatic Hydrocarbons Contents (mg/L) 10-: 2.4 X 10-I 2.7 X 10-' 7.8 X 10' 1.1 X 10-2 5.0 X 10-2 2.7 X 10-2 3.3 4.0 X lo-' 7.7 X 10-' 1.1 X 10-1 5.3 X 101 9.9 X 10-l 9.3 X 10-l 1.3 X 10-1 6.2 X 10' 1.6 X 10-1 6.5 X 10-1 1.1X 10-1 5.8 X 101 3.0 X lo-' 4.1 X le1 1.1X 10-' 4.7 X 101 2.1 X 10-1 6.0 X lo9 6.2 X 7.8 1.3 X 10-' 3.0 X lo-' 1.7 X lo-' 9.0 2.4 X 3.8 X 2.7 X 3.6 3.5 x 10-9
le2 10-3 10-2
10-9 10-3 10-3
4.7 x 10-3 1.6 X 10-l 1.7 X 10-l 3.2 X 10-2 1.4 X le2 1.8 X 7.4 x 10-3 2.7 X lo3 1.0 X 10-l 1.3 X le2 1.0x 10-2 4.0 X 4.0
5.9 x 3.2 X 2.1 X 2.2 x 3.1 X 2.8 X 2.5 X 8.0 X 4.7 x 1.8 X 3.8 X 9.9 x 1.3
10-3 10-3 10-2
10-3
10-2 10-2
10-2 10-9
2.6 5.2 4.6 1.1 7.6 X 5.2 X 9.7 X 2.6 X 1.2 x 3.1 X 6.5 X 3.4 x 3.4 x
10-I
10-1
lo-' 10-2 10-1 10-2 10-3
10-2 102
lo2 10' 101 lo2 102
102 10'
10' 10'
3.0 X 3.0 2.9 X 3.5 x 5.4 x 4.5 x 4.0 6.4 4.7
101 101 10' 10' 101
2.9 X 2.7 2.4 X 2.8 x 4.1 X 3.3 x 3.7 3.3 3.1
101 10' 10' 101 101
1.1x 10' 3.5 2.6 3.0 1.9 9.3 2.2 1.4 1.2 x 10' 4.2 X 10-1 1.8 X 10-1 3.1 3.2 4.4 x 10-1 1.0 x 10-1 5.0 X 10-1 3.5 x 10-1 5.9 4.3 2.2 8.4 X 10-l 2.0 x 10-1 8.6 X 1.7 2.3 X 10-1 1.2 x 10-1 2.1 8.5 X 10-1 1.3 X 10-l 3.6 X 1W2 1.8 x 10-2 7.3 X lo-' co.01 3.1 X 10-1
