Effects of external cooled EGR on particle number emissions under cold and warm spark-ignition direct-injection engine conditions

Abstract

External cooled exhaust gas recirculation (EGR) is drawing significant attention in downsized boosted spark ignition direct injection (SIDI) engines due to its potential to improve fuel economy. Meanwhile, worldwide emission standards pressure to reduce particle number (PN) emissions is generating great challenges for SIDI engine development. Thus it is necessary to examine the PN emission behaviors when implementing cooled EGR as a fuel-saving technology. In this study, the low-load with cold-engine (40 °C and 60 °C coolant temperature) and high-load with warm-engine (90 °C coolant temperature), representing high particle emission engine operating conditions over new European driving cycle, were chosen to understand the effects of cooled EGR on PN emissions in a downsized boosted SIDI gasoline engine using Horiba MEXA SPCS1000 PN measurement instrument. Measurements indicate that increasing cooled EGR levels provide higher PN emissions at low-load cold-engine operation, however, lower PN emissions at high-load warm-engine operation. This study, therefore, provides insight how cooled EGR impacts PN emissions under cold and warm engine operation.