Modelling of ignition mechanisms and pollutant formation in direct-injection diesel engines with multiple injections

Abstract

Multiple injections are an important aspect in modern direct-injection diesel engine development. The representative interactive flamelet (RIF) model, which was successfully used previously for simulations of diesel engine combustion, was recently extended to model multiple injections. In this paper this new RIF model is applied to model ignition and combustion with a pilot and a main injection with various dwell times, start of injection timings, and loads. Special emphasis is placed on the ignition of the main injection. It is shown that, for the investigated cases, the main injection does not auto-ignite but it is ignited by a strained premixed flame that propagates from the pilot injection to the mixture field of the main injection. The structure of that flame and the influence of the scalar dissipation rate on the propagation speed are investigated in detail. In addition to pressure curves, modelling results for NOx and soot emissions are compared with experimental data, showing good agreement.