Prediction of the Rate of Heat Release of Mixing-Controlled Combustion in a Common-Rail Engine with Pilot and Post Injections

Abstract

A one-dimensional model for the prediction of the rate of heat release (ROHR) in common-rail direct-injection diesel engines with pilot, main, and post injections is developed. The model is an improvement on the previously developed mixing-controlled combustion model extended by including the effect of the wall jet. The decay of the ROHR curve has been improved in the second regime of combustion. It was observed that the input kinetic energy of the wall spray is retarded only after the growth of spray along the bowl wall exceeds the diameter of the spray cone. It is shown that this model can be extended for engines with multiple injections, i.e. pilot, main, and post injections. The ROHR was modelled as a function of the turbulence kinetic energy of the fuel mass and the dissipation rate of this energy in different stages of spray propagation. The inputs required for the model are the nozzle discharge coefficient, the injection pressure, the injection timing, and the injected fuel quantity for each injection stage that are readily controlled in common-rail engines. The predicted heat release histories corresponding to the pilot injection, the main injection, and the post injection were found to be in agreement with the experiments.

Keywords

one-dimensional model rate of heat release common-rail direct-injection diesel engine pilot main and post injections

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