Sources of Particulate Matter Emissions Variability from a Gasoline Direct Injection Engine

Ultrafine particulate matter (PM) emissions from gasoline direct injection engines are a concern due to their associated health effects. This experimental study investigated sources of PM emissions variability observed in previous work, along with the effect of ethanol content in gasoline on PM emissions. Engine operating parameters and test conditions were studied and controlled, but could not account for the level of variability observed. FTIR measurements of gas phase hydrocarbon emissions provided evidence that fuel composition changes were responsible for this variability. Exhaust emissions of toluene and isobutylene were interpreted as markers of gasoline aromatic content and gasoline volatility, respectively. Tests with gasoline containing added toluene (10%) supported this hypothesis and showed that the PM emissions variability can be attributed to changes in the composition of the pump gasoline. Tests with gasoline containing added ethanol (10% and 30%) increased PM emissions at steady-state operation and decreased emissions during engine start-up.