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A literature review was conducted to survey recent research on the effects of fuel properties on exhaust emissions from gasoline and diesel vehicles, on-road and off-road. Most of the literature has been published in SAE papers, although data have also been reported in other journals and government reports. A full report and database are available from the Coordinating Research Council (www.crcao.org). The review identified areas of agreement and disagreement in the literature and evaluated the adequacy of experimental design and analysis of results. Areas where additional research would be helpful in defining fuel effects are also identified. In many of the research programs carried out to evaluate the effect of new blendstocks, the fuel components were splash blended in fully formulated fuels. This approach makes it extremely difficult to determine the exact cause of the emissions benefit or debit.

The analysis of data from the Auto/Oil Air Quality Improvement Research Program (AQIRP) study of the effect of aromatics, MTBE, olefins, and T90 on mass exhaust emissions from current (1989) vehicles was extended to include individual vehicles during individual operating modes. The results of the modal data analysis agree with and complement results which have been reported previously by AQIRP. Beyond this, attention is focused on three fuel compositional changes where the effect on emissions shows a reversal in sign depending on the vehicle operating mode chosen.

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.

In this portion of the Auto/Oil Air Quality Improvement Research Program, ten 1989 model vehicles were tested using two fuels with different sulfur levels. These tests were run to determine instantaneous effects on exhaust emissions, not long-term durability effects. The high- and low-sulfur fuels contained 466 ppm and 49 ppm sulfur, respectively. Mass exhaust emissions of the fleet decreased as fuel sulfur level was reduced. Overall, HC, CO, and NOx were reduced by 16, 13, and 9 percent, respectively, when fuel sulfur level decreased. This effect appeared to be immediately reversible. Engine-out mass emissions were unaffected by changes in the fuel sulfur content, therefore, tailpipe emissions reductions were attributed to increased catalyst activity as the sulfur level was reduced.

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.