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.
This project consists of two parts:
In the first part we have develop a new cavitation model based on Eulerian stochastic fields (ESF). The turbulence modeling approach is large eddy simulation. The model has been validated and tested with results from cavitation experiments performed at Chalmers Division of Combustion within the previous SNIC project 2017/1-104. The student Boxiong Chen has been working on this and is in his final year of his Ph.D. He will use this resource to perform further parameter studies (e.g. to investigate the impact of the number of stochastic fields on the statistical fidelity of the results) with the ESF model and to investigate cavitation in sprays from the engine combustion network (ECN).
In the second part of the project we will use the results from the cavitation simulations as input for a spray simulation in a reciprocating engine. The focus will be on numerical investigations of the impact of cavitation on spray formation and fuel-air mixing in engines. An LES approach will be used for modeling turbulence. The results will provide important information an mixture formation in engines, in particular direct injected gasoline engines operating under stratified conditions.