A Spark Ignited Engine and Flow Reactor Study of the Effect of an Organic Fuel Additive on Hydrocarbon and Nox Emissions

An experimental study was conducted to determine if an organic fuel additive could reduce engine out hydrocarbon and NO_x emissions. A production four cylinder spark ignited engine with throttle body fuel injection was used for the study. A full boiling range base fuel, an additized base fuel, a base fuel with methyl tertiary butyl ether (MTBE) and a base fuel with MTBE and additive were used in the engine tests. Additive concentration was 1/2% by mass. Hydrocarbon and NO_x measurements were recorded for 11 load/speed conditions. Hydrocarbon speciation data was taken at two of these conditions. The data from the experiments was analyzed in a pair-wise fashion for the fuels with and without the additive to determine whether statistically significant changes occurred. The results of the analysis indicated that, at a 95% confidence level, the additive reduced hydrocarbon emissions an average of 2.7% and increased NOx emissions an average of 3.5% when it was added to the base fuel blended with MTBE. No statistically significant effects of the additive were identified in the results of the speciation data. To study the effects of the additive in more detail, a high pressure flow reactor was used to react pure and additized fuels. Iso-octane, toluene, and toluene + MTBE were used in the flow reactor. The additive concentration was varied between 0-2% by mass. As an indicator of overall reactivity, carbon monoxide was measured while maintaining pressure and residence time constant. Next, speciation data was taken for a range of residence times at constant pressure and temperature. Speciation and CO data suggest that the additive increases the reaction rate of the pure fuels.