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Journal Article

Review of Prior Studies of Fuel Effects on Vehicle Emissions

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 ( 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.
Technical Paper

Effect of Gasoline Olefin Composition on Predicted Ozone in 2005/2010 - Auto/Oil Air Quality Improvement Research Program

The effect of gasoline olefin composition and content on urban ozone was estimated using the Urban Airshed Model (UAM), emission measurements for a base fuel, and projected emissions for two hypothetical fuels with reduced olefin content. The projected emissions for the hypothetical fuels were developed using regressions developed from Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase I testing, a vapor headspace model and other information. Ozone modeling was conducted for Los Angeles in year 2010 and Dallas-Fort Worth and New York in year 2005. When all olefins were removed from the base fuel, the light-duty vehicle contribution to peak hourly ozone was reduced by 8 to 12%. This corresponds to a projected reduction of 0.6 to 0.8% in total peak ozone from all sources. Removing only light (C5) olefins provided 67 to 78% of the peak ozone benefit from removal of all olefins.
Technical Paper

Effects of Fuel Properties on Mass Exhaust Emissions During Various Modes of Vehicle Operation

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.
Technical Paper

The Autoignition Chemistries of Primary Reference Fuels, Olefin/Paraffin Binary Mixtures, and Non-Linear Octane Blending

The chemistries controlling autoignition of primary reference fuels (n-heptane/isooctane binary mixtures) and binary olefin/paraffin mixtures have been inferred from experimental motored-engine measurements. For all n-heptane/isooctane and olefin/paraffin mixtures, each component of the mixture reacted via parallel intramolecular mechanisms with the only interactions being via small labile radicals. The octane qualities of the neat components appears to be dictated not by the initial reaction rate of the fuel, but by the reaction rate of the subsequent fuel-product reactions. In contrast, the blending octane quality of a component appears to be dictated more by the rate of the initial fuel reactions. The abnormally high blending octane qualities of olefins result from them having high rates of initial fuel reaction combined with slow rates of subsequent fuel-product reactions.
Technical Paper

Effects of Gasoline Composition on Vehicle Engine-Out and Tailpipe Hydrocarbon Emissions - The Auto/Oil Air Quality Improvement Research Program

In this pilot study conducted by the Auto/Oil Air Quality Improvement Research Program, engine-out and tailpipe speciated hydrocarbon emissions were obtained for three vehicles operated over the Federal Test Procedure on two different fuels, both of which were speciated. The fates of the fuel species were traced across the engine and across the catalyst, and relationships were developed between engine-out and tailpipe hydrocarbon emissions and fuel composition. These relationships allowed separating the fuel's contribution to engine-out and tailpipe hydrocarbon emissions into two parts, unreacted fuel and partial oxidation products. Specific ozone reactivities and toxic air pollutants were analyzed for both engine-out and tailpipe emissions. Vehicle-to-vehicle, fuel-to-fuel, and bag-to-bag differences have been highlighted.
Technical Paper

Effects of Gasoline Sulfur Level on Mass Exhaust Emissions - Auto/Oil Air Quality Improvement Research Program

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.
Technical Paper

Description of Auto/Oil Air Quality Improvement Research Program

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.
Technical Paper

Effects of Gasoline Composition and Properties on Vehicle Emissions: A Review of Prior Studies - Auto/Oil Air Quality Improvement Research Program

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.
Technical Paper

The Chemical Origin of Fuel Octane Sensitivity

Autoignition chemistries of several paraffins, olefins, and aromatics were examined in a motored engine at different engine conditions. Paraffin chemistry was dominated by “negative-temperature coefficient” (NTC) behavior which became more pronounced at lower pressures, higher temperatures, and shorter reaction times. In contrast, olefin and aromatic chemistries did not exhibit NTC behavior. Measured pressures and calculated temperatures at fired octane rating conditions showed slightly lower pressures, higher temperatures, and lower reaction times at Motor octane rating conditions when compared to Research conditions. Therefore, paraffins would have a more pronounced NTC behavior under Motor rating conditions than under Research conditions.