Combustion System Development Trends for Multi-Valve Gasoline Engines 900652
The expected future exhaust emission standards for passenger cars with gasoline engines require a further reduction of the raw exhaust emissions. In connection with this, for larger engines and cars, an emphasis must be put on HC reducing measures, while for smaller engines and cars, Nox-emission reduction is very important. Moreover, a further reduction of fuel consumption is imperative. To reduce the Nox-emissions and also to improve efficiency, exhaust gas recirculation (external or internal) is a well proven measure. Among other measures, reduced fuel enrichment demand during warm up is desirable in order to minimize HC-emission. Both exhaust gas recirculation and minimized fuel enrichment during warm up require a good combustion system tolerance to burning highly diluted mixtures without misfiring. These demands on the combustion system are comparable with those for a good lean burn capability.
In particular, for multi valve engines measures to improve the lean burn capability and the tolerance against exhaust gas recirculation have been discussed on the basis of experimental investigations. The important role of an adjustment of the charge flow in the cylinder will be demonstrated. The results of gas sampling experiments which were carried out with a very high time resolution to detect the local air fuel ratio in the cylinder have been considered to explain the positive effects which charge stratification can have on the combustion behavior.