Grenzpotenziale von ottomotorischen Magerbrennverfahren hubraumkleiner aufgeladener Motoren mit Direkteinspritzung

Within the scope of this thesis a new lean burn process combining homogeneous and stratified charge combustion for reducing the fuel consumption of turbocharged spark ignited direct injection engines is presented. It is widely recognised that the operation of spark ignited engines with excess air is one of the most promising methods to achieve a large fuel consumption improvement. The combination of lean burn combustion with technologies like for instance a variable valve train, an increased charge motion, an innovative ignition system or an improved turbocharger offers enormous potential for reducing fuel consumption and consequently also CO2 emissions of small capacity engines with turbocharging and direct injection. After considering the current state of scientific knowledge and developing a strategy for achieving a large fuel consumption improvement on the one hand and a reduction of nitrogen oxide emissions on the other hand experimental investigations on diverse single- and four-cylinder engines were carried out in order to quantify these potentials.
The findings can be summarised as follows:
- By combining the homogeneous-lean, homogeneous stratified and the strat ified
charge combustion in one engine map a significant benefit in fuel consumption
can be achieved.
- To limit the additional expenses regarding the exhaust gas aftertreatment the
engine-out nitrogen oxide emissions have to be reduced. Therefore, the dilution
of the mixture has to be maximised. Depending on the engine operation
point, the residual-gas/ air mixture should be adjusted.
- A significantly increased charge motion allows a reduction of pollutant emissions in lean operation as well as an expansion of the engine load range operated so far.
- A high level of charge motion does not conflict with the stratified charge combustion at low part load in general.