LES of cavitation in nozzles
Improvements in the fuel injection systems of internal combustion engines can substantially reduce the emission of harmful pollutants. The fuel injection system produces the spray, which directly affects the combustion of the fuel, which in turn determines the production of pollutants. Current common-rail fuel injection systems for direct injection diesel engines operate at very high pressures, up to 1800 bar, while the whole injection process lasts for very short time intervals – of just a few milliseconds. The injection rate is controlled through the fast opening and closing of the needle valve, whereas the typical diameter of nozzle holes is 0.1–0.2 mm. As the flow from the injector enters into the nozzle discharge holes, it has to turn sharply from the needle seat area, which leads to the static pressure of the liquid at the entrance of the holes falling below its vapour pressure and initiation of cavitation. The occurrence of cavitation in orifices and its significant effect on spray formation have been known for quite some time. In this project we develop a new cavitation model based on Eulerian stochastic fields. The turbulence modeling approach is large eddy simulation. The model will be validated and tested with results from cavitation experiments performed at Chalmers Division of Combustion.