Spark ignition (SI) engines are susceptible to excess emissions at low ambient temperatures. Direct injection leads to the formation of particulate matter (PM), and direct injection spark ignition (DISI) engines should show greater PM emissions at low ambient temperatures. This study compares excess emissions of gaseous and solid pollutants following cold start at a low ambient temperature and the standard test temperature. Euro 5 passenger cars were tested on a chassis dynamometer within BOSMAL's climate-controlled test chamber, according to European Union legislation (−7°C over the urban driving cycle (UDC), and at 25°C). Two vehicles were also tested over the entire New European Driving Cycle (NEDC). Emissions of regulated compounds and carbon dioxide were analyzed; particulate emissions (both mass and number) were also measured, all using standard procedures. Over the UDC, changes in emissions of hydrocarbons (HC), carbon monoxide (CO), and CO2 were unequivocal; the situation for oxides of nitrogen (NOx) was somewhat more complex. Over the entire NEDC, excess emissions were observed (though much larger for the UDC). The increase in CO2 emissions over the entire NEDC was 17% for the MPI vehicle and 15% for the DISI vehicle. DISI particle number emissions increased by ∼50%; DISI particle mass by >600%. A simple mathematical correction for the difference in ambient temperature was applied to the results. Excesses are greatest following start-up, but persist for hundreds of seconds. The temperature of the intake air had a measurable effect on certain emissions, even after the engine had been running for some time.
