Fuel composition effects on emissions from a spark ignition engine

The EPA recently enacted regulations affecting the manufacturers of reformulated fuels. Specifically, the regulations limit the presence of formaldehyde, acetaldehyde, butadiene and benzene in exhaust emissions of engines burning reformulated fuels. In order to understand the relationship between fuel formulation and these compounds, experiments have been performed to determine the effect of fuel composition on the constituents of the unburned hydrocarbon (UHC) emissions from a spark ignition engine. The fuels studied consist of the base fuel, iso-octane, blended with varying concentrations of toluene. Toluene was selected as the blended fuel in these experiments because of its high concentration in unleaded gasolines.An increase of the toluene concentration in the fuel produced several effects, most of which are interrelated: Flame temperature increased with increasing toluene concentration resulting in higher NO_x and lower total unburned hydrocarbons. The increase in flame temperature caused more iso-octane to be oxidized. Toluene contributed to the production of benzene and benzaldehyde. The current mechanisms for toluene and iso-octane oxidation support these results.