Abstract
Conversion of pollutants in the catalyst initiates when a minimum catalyst temperature is reached. Retarding the ignition timing beyond top dead centre firing is a widely used method for effective catalyst heating using the engine exhaust enthalpy. The emissions during these first seconds of engine use dominate cumulative tailpipe emissions over typical drive cycles. Furthermore, downsizing, combined with turbocharging, leads to extended catalyst light-off times, as the exhaust enthalpy must also heat the turbocharger casing. However, future legislation will tighten the emission standards. In particular, the particulate emissions of gasoline direct injection engines have increased in importance in recent years, primarily because the number of particles emitted by a vehicle will be regulated by the upcoming Euro 6 exhaust gas emission standards. This paper discusses the impact of injection pressures above the standard of 200 bar on the catalyst heating operation. Direct injection with a centrally positioned injector enables a wide range of parameters for both injection splitting and injection timing. For example, the possibility to inject a small quantity of fuel close to the ignition timing stabilizes ignition and combustion robustness but also can increase soot formation. So, optimizing mixture formation by managing evaporation rates and fuel penetration depths is essential to avoid or minimize particle formation, especially under cold engine conditions. Increasing the injection pressure is a promising approach to improve the catalyst heating performance of gasoline direct injection spark ignition engines while maintaining low particulate emissions.
