Abstract
The downsized boosted spark-ignition direct-injection (SIDI) engine is a viable technology for improving vehicle fuel economy. However, higher soot levels associated with operating the engine at significantly higher loads provide additional challenges for meeting future stringent emission regulations. In this study, we investigate the effects of exhaust gas recirculation (EGR) on soot emission levels for a 2.0 L boosted SIDI engine. Three higher load conditions (1000 rpm 210 Nm, 1500 rpm 260 Nm, and 2000 rpm 250 Nm) are examined to characterize soot emission levels with increasing EGR ratio up to 20%. An increase in EGR level provides lower soot emission levels. At 1500 rpm and 260 Nm, for example, soot emissions are reduced by nearly 50% with approximately 20% cooled EGR. Two factors are considered as primary contributors toward the reduced soot emissions with EGR: 1) lower spray penetration and reduced wall wetting, 2) lower combustion temperature within localized rich fuel pockets and within pool fire regions that may occur on piston and cylinder wall surfaces.
