An overview of cold start emissions from direct injection spark-ignition and compression ignition engines of light duty vehicles at low ambient temperatures

Abstract

Spark-ignition (SI) engines are highly susceptible to excess emissions when started at low ambient temperatures, a phenomenon which has been widely discussed in the literature. Direct injection diesel engines feature a markedly different fuelling and combustion strategy, and as such their emissions behaviour is somewhat different from gasoline engines. The excess emissions of diesel engines at low ambient temperatures should also differ. The aim of this study was to compare excess emissions of gaseous and solid pollutants over a legislative driving cycle (the New European Driving Cycle, NEDC) following cold start at a low ambient temperature for both engine types. This paper examines emissions at low ambient temperatures with a special focus on cold start; emissions are also compared to start-up at a higher ambient temperature (24 °C). The causes of excess emissions andfuel consumption are briefly discussed. A series of tests were performed on European Euro 5 passenger cars on a chassis dynamometer within an advanced climate-controlled test laboratory at BOSMAL Automotive Research and Development Institute, Poland. Emissions data obtained over the Urban Driving Cycle by testing at 24 °C and at -7 °C, are presentedfor a selection ofmodern Euro 5 gasoline and diesel vehicles representative of the European passenger carfleet. A full modal emissions analysis was also conducted at 24 °C and at -7 °C over the NEDC. Emissions andfuel consumption were substantially higher at -7 °C than at 24 °C.