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Prior studies of the effect of gasoline composition and physical properties on automotive exhaust and evaporative emissions have been reviewed. The prior work shows that the parameters selected for investigation in the Auto/Oil Air Quality Improvement Research Program (AQIRP) - gasoline aromatics content, addition of oxygenated compounds, olefins content, 90% distillation temperature, Reid vapor pressure, and sulfur content - can affect emissions. Effects have been observed on the mass of hydrocarbon, CO, and NOx emissions; on the reactivity of emissions toward ozone formation; and on the emissions of designated toxic air pollutants. The individual effects of some of the AQIRP parameters have been studied extensively in modern vehicles, but the most comprehensive studies of gasoline composition were conducted in early 1970 vehicles, and comparing the various studies shows that fuel effects can vary among vehicles with different control technology.

An overview of Phase 1 of the Auto/Oil Air Quality Improvement Research Program is presented. Specific information is provided on each of the individual test fuel matrices that were conducted to investigate vehiclelfuel “system” effects on emissions. Procedures for sampling exhaust, evaporative, and running loss vehicle emissions are described, as well as techniques developed for speciation of individual hydrocarbons. Air quality models to project ozone reduction potential of reformulated gasolines and methanol, and economic studies to estimate the relative cost-effectiveness of the vehiclelfuel alternatives are also briefly explained.

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.

Fuel effects on exhaust emissions of a sample of seven high emitting vehicles were studied. The vehicles had various mechanical problems and all ran fuel rich. The degree of enrichment varied between tests, and strongly affected mass emissions. Variable enrichment can cause incorrect apparent fuel effects to be calculated if not accounted for in data analysis. After variable enrichment was compensated for, the percentage effects of fuel oxygen, RVP, and olefins were largely in agreement with prior findings for normally emitting vehicles. Reducing fuel sulfur and T90 may have less benefit on hydrocarbon emissions in these high emitters than in normal emitters, and reducing sulfur may have less benefit on CO emissions. Reducing aromatics may be somewhat more helpful in reducing hydrocarbon and CO emissions in the high emitters.

Species analyses have been performed on engine-out and tailpipe hydrocarbon mass emissions to help understand why fuels with increasing amounts of heavy hydrocarbon constituents produce significantly higher tailpipe hydrocarbon emissions. Mass and speciated hydrocarbon emissions were acquired for a fleet of ten 1989 model year vehicles operating on twenty-six fuels of differing heavy hydrocarbon composition. These fuels formed two statistically designed matrices: one examining the effects of medium, heavy, and tail reformate and medium and heavy catalytically cracked components; and the other examining the effects of heavy paraffinic versus heavy aromatic components and the effects of the 50% distillation temperature. In this paper the fates of fuel species were traced across the engine and across the catalyst, and correlations were developed between engine-out and tailpipe hydrocarbon species emissions and fuel composition.

Modal analyses have been performed on engine-out and tailpipe hydrocarbon and carbon monoxide mass emissions to help understand why fuels with increasing amounts of heavy hydrocarbon constituents produce significantly higher tailpipe hydrocarbon emissions, yet do not produce significantly higher tailpipe carbon monoxide emissions. Mass emissions were acquired for a fleet of ten 1989 model year vehicles operating on twenty six fuels of differing heavy hydrocarbon composition. These fuels formed two statistically designed matrices: one examining the effects of medium, heavy, and tail reformate and medium and heavy catalytically cracked components; and the other examining the effects of heavy paraffinic versus heavy aromatic components and the effects of the 50% distillation temperature.

Emission effects of gasoline hydrocarbon components distilling above 300°F were investigated to determine whether the effect of 90% distillation temperature (T90) found in an earlier Auto/Oil Program study is due to fuel distillation properties or to hydrocarbon composition, and also to determine whether the T90 effect is linear. Twenty-six fuels were tested in two sets. In Matrix A, the independent variables were catalytically cracked (FCC) and reformate stocks with nominal distillation ranges of 300 to 350, 350 to 400 and 400+°F. In Matrix B, the independent variables were a reformate stock (320 to 370°F), a heavy alkylate (330 to 475°F), and a light alkylate distilling below 300°F, which was used to vary fuel T50 at fixed levels of T90. Exhaust mass and speciation were measured using ten 1989 vehicles of the Auto/Oil Current Fleet. Tailpipe hydrocarbon emissions were found to increase nonlinearly with progressive addition of the heavier components.

Three-day diurnal SHED evaporative emissions were measured in a fleet of ten Auto/Oil current (1989) and 2 older (1984) vehicles using Auto/Oil Industry Average fuel. SHED temperature cycled each 24-hour period from 72 to 96 F (22.2 to 35.5C). Measurements included speciation of individual hydrocarbons in the SHED as well as total mass emissions at the end of each of the three 24-hour test periods. Previous evaporative emission studies provided evidence that permeation and/or fuel seepage could contribute significantly to the mass of diurnal and hot soak emissions. Data from this investigation were used to quantify the contribution of liquid fuel to total SHED emissions during diurnal testing. A calculation method, based on the concentration of 29 select hydrocarbons in the SHED, is presented to apportion SHED emissions between those associated with liquid fuel losses and those associated with fuel tank head space vapor losses.

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).

Simultaneous tests of emissions and driveability conducted at 4.4°C on a chassis dynamometer using 10 late model vehicles showed a strong correlation between degraded driveability and increased tailpipe hydrocarbon emissions. Other regulated emissions were uncorrelated to driveability, or were small in magnitude. The 24 test gasolines were systematically varied in front-end, mid-range, and tail-end volatility and so spanned much of the moderate and high DI (driveability index) fuel region. Splash blends of 10%.vol ethanol and 15%vol MTBE blended gasolines were tested in addition to hydrocarbon gasolines.

Engine after-run, sometimes referred to as “run-on” or “dieseling,” has existed for many years, but seems to be occurring more frequently with late-model cars and low-octane gasolines. A vehicle study was conducted to gain a better understanding of the factors that influence after-run. Engine operating variables, such as high idle speed, lean idle mixture, and retarded basic spark timing, all increased after-run frequency by increasing the throttle opening (intake charge density). Reduced Research-octane number of the gasoline also increased after-run frequency, but Motor-octane number and hydrocarbon composition did not have any effect. After-run exhaust contained about 125 times more aldehydes than engine idle exhaust, and it caused eye irritation and an obnoxious odor. Compression ignition, rather than surface ignition, is most likely the cause of after-run.

Although the control of nitrogen oxides from automobile exhaust is not yet required by law, several methods have been investigated to determine how much control is possible and what penalties result. These methods involved spark timing, carburetion, and exhaust recirculation. On one test car, a control system was developed which reduced nitrogen oxides 74% while maintaining hydrocarbon and carbon monoxide control at current (1968) federal levels. However, a 13% loss in fuel economy was incurred, and driveability problems were observed. Application to other car models, deposit accumulation, durability, and performance under extreme weather conditions are all open questions at this time.

A manganese fuel additive, MMT, is now being used in many unleaded gasolines to improve their octane quality. Use of MMT at concentrations up to 0.033 g Mn/ℓ (0.125 g Mn/gal) is expected to increase. To determine the effect of MMT on exhaust emission control systems, five cars were tested for 80 000 km (50,000 miles) using a driving schedule which included 113 km/h (70 mph) steady speed driving. In this type of operation, use of MMT caused: plugging of monolithic converters located close to the exhaust manifold; partial plugging of an underfloor bead converter; an increase of hydrocarbon emissions from the engines; and excessive spark plug deposits. However, use of MMT apparently enhanced catalytic converter oxidizing activity and did not substantially affect octane requirement increase. These preliminary data suggest that use of MMT in commercial gasolines may cause problems with exhaust emission control systems now in use.