Possibilities of simultaneous in-cylinder reduction of soot and NOx emissions for diesel engines with direct injection

Abstract

Up to now, diesel engines with direct fuel injection are thepropulsion systems with the highest efficiency for mobileapplications. Future targets in reducing CO2-emissions with regardto global warming effects can be met with the help of theseengines. A major disadvantage of diesel engines is the high sootand nitrogen oxide emissions which cannot be reduced completelywith only engine measures today. The present paper describes twodifferent possibilities for the simultaneous in-cylinder reductionof soot and nitrogen oxide emissions. One possibility is theoptimization of the injection process with a new injectionstrategy the other one is the use of water diesel emulsions withthe conventional injection system. The new injection strategy forthis experimental part of the study overcomes the problem ofincreased soot emissions with pilot injection by separating theinjections spatially and therefore on the one hand reduces thesoot formation during the early stages of the combustion and onthe other hand increases the soot oxidation later during thecombustion. Another method to reduce the emissions is theintroduction of water into the combustion chamber. Emulsions ofwater and fuel offer the potential to simultaneously reduce NOx and soot emissions while maintaining a high-thermal efficiency.This article presents a theoretical investigation of the use offuel-water emulsions in DI-Diesel engines. The numericalsimulations are carried out with the 3D-CFD code KIVA3V. The useof different water diesel emulsions is investigated and assessed with the numerical model.