Influence of Fuel Composition on Exhaust Emissions of a DISI Engine during Catalyst Heating Operation

Particle number measurements during different real world and legislative driving cycles show that catalyst heating, cold and transient engine operation cause increased particle number emissions. In this context the quality of mixture formation as a result of injector characteristics, in-cylinder flow, operation & engine parameters and fuel composition is a major factor. The goal of this paper is to evaluate the influence of different biogenic and alkylate fuels on the gaseous and particle number emission behavior during catalyst heating operation on a single-cylinder DISI engine. The engine is operated with a late ignition timing causing a high exhaust enthalpy flow to heat up the catalyst, a slightly lean global air fuel ratio to avoid high hydrocarbon emissions and a late injection right before the ignition to reduce the coefficient of variance of the indicated mean effective pressure. While the local fuel enrichment through the late injection helps to stabilize the inflammation and combustion process it can also lead to very high particle number emissions due to poor mixture formation. Based on the experimental results with RON 95 fuel the particle emission behavior with different biogenic fuel blends (E40, B40), alkylate fuels and toluene is examined. The variation of the fuel composition shows how certain molecules (aromatics, alcohol) affect the particle emissions while the adaption of the boiling curve directly influences the mixture formation in general. Furthermore, the results demonstrate the potential of biofuels to reduce the particle number emissions of modern GDI engines.