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Diesel engines continue to offer outstanding benefits in fuel consumption and durability over other engine types. Recently however, the environmental impact of diesel engines has become an increasingly critical factor and has a significant influence on diesel engine development trends. The fuel injection system is one of the most important keys to fulfill the stringent exhaust emissions standards while still maintaining the fuel economy and related CO2 emission benefits of the diesel engine. Research has shown that, to a significant extent, by using the technique of fuel preinjection, DI diesel engines can simultaneously reduce NOx levels and particulate emissions while also improving the level of combustion noise. In addition, the technique has demonstrated the possibility to address these environmentally-focused goals while maintaining low fuel consumption, a characteristic strength of diesel engines, which is directly related to the reductions in CO2 emissions.

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.

The paper compares the development potential of high speed DI Diesel engines with production IDI Diesel engines. Possibilities to overcome the critical NOx emission and combustion noise problems are discussed and their effectiveness is evaluated. The fuel consumption advantages both for a European emission standards tuning and a tuning to meet todays US Federal Standards are figured out to be about 15% and 10%. The possibilities to realize a methanol high speed DI Diesel engine are also discussed.