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Exhaust emissions were measured as a function of gasoline composition in two fleets of vehicles - 20 1989 vehicles and 14 1983-1985 vehicles. Eighteen different gasolines were tested which varied in aromatic, olefin, and MTBE content and in the 90 percent distillation temperature (T90). Subject to the cautions and qualifications described in the body of this paper, mass exhaust emissions in both fleets of vehicles were affected by changes in fuel composition. Responses to changes in MTBE and olefins were similar in both fleets: adding MTBE reduced emissions of HC and CO, and reducing olefins lowered emissions of NOx while raising emissions of HC. In the current fleet, reducing aromatics lowered HC and CO, while in the older fleet, reducing aromatics raised HC and lowered NOx. In the current fleet, lowering T90 reduced HC over 20%, while raising NOx slightly. In the older fleet, lowering T90 reduced HC by only 6%.

This paper presents results derived from Phase I of the Auto/Oil Air Quality Improvement Research Program. The Clean Air Act-defined mobile source toxic air pollutants benzene, 1,3-butadiene, formaldehyde and acetaldehyde have been measured in exhaust from twenty current model vehicles and fourteen older model vehicles during testing with 18 gasolines of varying composition. The gasoline fuel compositional variables evaluated included aromatic content, methyl tertiary-butyl ether (MTBE) content, olefin content, and the 90% distillation temperature (T90). The four fuel parameters were varied at target values of 45 and 20 vol % total aromatics, 0 and 15 vol % MTBE, 20 and 5 vol % total olefins and 360 and 280 °F 90% distillation temperature. An industry average fuel and an emissions certification test fuel were tested as reference fuels. In the current fleet, benzene levels were lowered when either fuel aromatics or T90 were reduced.

This report presents the Auto/Oil AQIRP results of a methanol fueled vehicle emission study. Nineteen early prototype flexible/variable fueled vehicles (FFV/VFV) were emission tested with industry average gasoline (M0), an 85% methanol-gasoline blend (M85), and a splash-blend of M85 with M0 (gasoline) giving 10% methanol (M10). Vehicle emissions were analyzed for the FTP exhaust emissions, SHED diurnal and hot soak evaporative emissions, and running loss evaporative emissions. Measurements were made for HC, CO and NOx emissions and up to 151 organic emission species, including air toxic components. M0 and M10 emissions were very similar except for elevated M10 evaporative emissions resulting from the high M10 fuel vapor pressure. M85 showed lower exhaust emissions than M0 for NMHC (non-methane hydrocarbon), OMHCE (organic material hydrocarbon equivalent), CO and most species. M85 had higher exhaust emissions for NMOG (non-methane organic gases), NOx, methanol and formaldehyde.

Exhaust and evaporative emissions were measured as a function of gasoline composition and fuel vapor pressure in a fleet of 20 1989 vehicles. Eleven fuels were evaluated; four hydrocarbon only, four splash blended ethanol fuels (10 vol %), two methyl tertiary-butyl ether (MTBE) blends (15 vol %) and one ethyl tertiary-butyl ether (ETBE) blend (17 vol %). Reid vapor pressures were between 7.8 and 9.6 psi. Exhaust emission results indicated that a reduction in fuel Reid vapor pressure of one psi reduced exhaust HC and CO. Adding oxygenates reduced exhaust HC and CO but increased NOx. Results of evaporative emissions tests on nineteen vehicles indicated a reduction in diurnal emissions with reduced Reid vapor pressure in the non-oxygenated and ethanol blended fuels. However, no reduction in diurnal emissions with the MTBE fuel due to Reid vapor pressure reduction was observed. Reducing Reid vapor pressure had no statistically significant effect on hot soak emissions.

Species analyses have been performed on engine-out and tailpipe hydrocarbon mass emissions to help understand why fuels with higher T50 and/or T90 distillation temperatures produce higher engine-out and tailpipe hydrocarbon emissions and why fuels with higher T90 distillation temperatures produce higher engine-out and tailpipe specific reactivities. Species analyses were also performed to examine the effects of fuel sulfur level on engine-out and tailpipe species and specific reactivities. These analyses were performed on three different test-vehicle fleets representing varying levels of emissions control technology and the effect of emissions control technology was examined. Individual hydrocarbon species concentrations in both the engine-out and tailpipe were found to correlate linearly with the concentrations of the same species in the fuel, implying that a small fraction of the fuel escapes the combustion process and conversion over the catalyst.

Modal analyses have been performed on engine-out and tailpipe hydrocarbon mass emissions to help understand why fuels with higher T50 and/or T90 distillation temperatures produce somewhat higher engine-out hydrocarbon emissions and substantially higher tailpipe hydrocarbon emissions. Modal analyses were also performed to examine how increased fuel sulfur increases tailpipe hydrocarbon emissions and to identify which gasoline properties in this study are responsible for the lower tailpipe hydrocarbon emissions with reformulated gasolines. These analyses were performed on three different test vehicle fleets representing varying levels of emissions control technology. The modal analyses showed that the substantially higher tailpipe hydrocarbon emissions from fuels with high T50 and/or T90 distillation temperatures result primarily from these fuels producing substantially higher engine-out hydrocarbon emissions during the first cycle of the Federal Test Procedure (FTP).

Exhaust emissions of three vehicles fueled with compressed natural gas (CNG) were compared with emissions of three counterpart gasoline vehicles. The natural gas vehicles were tested on four CNG fuels covering a wide range of pipeline natural gas compositions. The gasoline vehicles were tested on AQIRP Industry Average gasoline and a reformulated gasoline meeting California 1996 regulatory requirements. Nonmethane hydrocarbon (NMHC) and toxic air pollutant emissions of the CNG vehicles were about one-tenth those of their counterpart gasoline vehicles, while methane emissions were about ten times those of the gasoline vehicles. Carbon monoxide (CO) and nitrogen oxides (NOx) emissions were more variable among the three vehicle pairs. CO emissions ranged from 20 to 80% lower with CNG than with gasoline, and NOx ranged from 80% lower with CNG to equivalent to gasoline.