Results of Quasi-Steady Evaporation Model Applied to Multi-Dimensional D.I. Diesel Combustion Simulation

The modeling of the combustion process inside D.I. compression ignition engines has become extremely important for both improving combustion efficiency and describing the conditions in which pollutant emissions formation occurs. However simulation codes results are greatly dependent on the history of fuel droplets injected into combustion chamber, which have to vaporize before mixing with air. Actually fuel jet evaporation phase is particularly critical as far as its rate is concerned. In fact it largely affecs the it initial period of the combustion process.

Simplified evaporation models can lead to unrealistic air-fuel ratio distribution in the combustion chamber and, as a consequence, to wrong heat release rate. An incorrect description of heat release rate still turns out into wrong evaluation of premixed and diffusive combustion periods, thus involving scarcely precise predicted profiles on both pressure and burned mass fraction.

In this paper an evaporation model developed starting from Hiroyasu's approach has been tested in comparison with the original one used in Kiva II code. Besides this test, also combustion process has been simulated by applying both the evaporation models to the above mentioned multi-dimensional code. The theoretical results of the proposed model, by accounting more accurately for the air-fuel mixture physical properties dependence on thermodynamic parameters, proved to be more consistent with the experimental ones. In fact both the droplet life evaluated in quiescent conditions and the calculated pressure and burned mass fraction diagrams showed a behaviour very close to measured data.