The Composition of Spark Ignition Engine Steady State Particulate Emissions 1999-01-1143

The contribution of spark ignition engine particulate emissions to total particulate emissions and the published data on SI engine emission levels are reviewed. There is a wide spread of published data and the worst SI engines would exceed the future diesel particulate emissions regulations. However, most modern SI engines with a catalyst will easily meet the future diesel particulate emissions regulations, although their particulates emissions are a significant fraction of these regulations. Steady state lambda 1 results are presented for a Ford Zetec SI engine at conditions representative of the urban driving cycle at 5 and 10kW power output and also at WOT. The impact of a cold start and EGR at the two low power conditions was also investigated. The particulate emissions for petrol were of the order of 5% of the future (2005) diesel emissions regulations and were approximately 20 mg/kg fuel (about 2 mg/mile or 1.3 mg/km). This was much lower than all reported results for particulate emissions for SI engines over a FTP or EC test cycle, indicating that the highest emissions were generated during transient operation. Analysis of the particulates showed that the bulk of the mass was ash and the second largest fraction was unburnt lubricating oil. Carbon emissions were only significant at high power WOT with fuel enrichment, at other conditions carbon was less than 10% of the total mass. At WOT rich operation the highest particulate emissions were recorded and these were 10 times the level at the 5 and 10 kW conditions and about 50% of the EC 2005 diesel particulate levels.