Heat Release in Direct Injection Engines

Abstract

An accurate model for the heat release rate in a modern DI diesel engine is newly evolved from the known mixing controlled combustion model. In this chapter, the combustion rate is precisely described by relating the mixing rate to the turbulent energy created at the exit of the nozzle as a function of the injection velocity and by considering the dissipation of energy in free air and along the wall. The complete absence of tuning constants distinguishes the model from the other zero-dimensional or pseudo multi-dimensional models, at the same time retaining the simplicity. Successful prediction of the history of heat release in engines widely varying in bores, rated speeds and types of aspiration, at all operating conditions validated the model. The earlier model has explained correctly the effect of kinetic energy of fuel injection. However, it considered only the spray in the air and the accuracy of prediction was only about 65%. In most of the engines of bore less than 130 mm, wall jet plays a very important role. By considering the wall jet in detail, the heat release has been explained to accuracy better than 95%. This was proved for a variety of engines. The bores range from 85 to 280 mm.