A new injection strategy with high potential to minimize soot and NO_x emissions for Diesel engines with direct injection

摘要

The main source for soot formation during the combustion of a diesel engine is the interaction of liquid fuel or a very rich air/fuel-mixture with the flame. This effect appears especially in modern direct injection engines where the injection is often split in a pre- and a main injection due to noise reasons and leads to high amounts of soot. The injection strategy for this experimental study overcomes this problem by separating the injections spatially and therefore on the one hand reduces the soot formation during the early stages of the combustion and on the other hand increases the soot oxidation later during the combustion. In particular an injection configuration is used which gives the degree of freedom to modify the injection in the described manner. Therefore the cylinder head of a heavy duty single cylinder research engine is equipped with a second common-rail injector. This second injector is used for the pilot injection which is injected centrally in the combustion chamber while the main injection is done in a conventional manner using a seven-hole injector. The results show that there is a potential to minimize the soot emissions significantly by using a spatially-separated pilot, and main injection without a disadvantage in NO_x emissions, especially at higher EGR-rates.