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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.

Onboard refueling control technology has been successfully applied to two vehicles with 98+% efficiency in tests with 10.5 RVP fuel at 84° F. The Onboard system, which controls exhaust, evaporative, refueling, and so called “running losses”, was constructed out of components found in current automotive evaporative control systems. During refueling, the tank vapors are forced into the enhanced charcoal canister by a flowing liquid seal in the fillpipe. The canister was removed from the engine compartment and mounted within the vehicle frame close to the fuel tank. Each vehicle demonstrates a different possible safe location from a crash worthiness viewpoint. In order to further improve safety by preventing the expulsion of liquid gasoline upon gas cap removal, the orifices in the production tank vent lines were removed so that the fuel tank is at atmospheric pressure at all times. As modified, no significant driveability differences from production vehicles were found.

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.

When automobiles are refueled, hydrocarbon vapors are displaced from the vehicle tank and emitted to the atmosphere. An experimental program was carried out to measure both the mass and the volume of these emissions as a function of three variables: vehicle tank temperature, dispensed fuel temperature, and fuel volatility measured as Reid vapor pressure. Based on the experimental results, regression equations were developed which can be used to accurately predict refueling emissions under a wide range of conditions. An analysis of the experimental results shows that the vapor balance system, the simpler, less expensive of the two systems being considered for control of refueling emissions, has the potential to meet strict standards under temperature conditions where ozone is likely to form in the atmosphere.