Development and validation of a CFD model for combustion simulations in direct injection diesel engines based on detailed chemistry and the unsteady diffusion flamelet assumption

In this work a CFD solver for combustion simulation in direct injection Diesel engines has been implemented in Lib-ICE, an OpenFOAM library for internal combustion engine simulations developed by the ICE group of Politecnico di Milano. The solver is based on the flamelet assumption, with a set of unsteady diffusion flames representing the Diesel combustion process according to the Representative Interactive Flamelet approach. Also different variants of this model were tested, namely the Eulerian Particle Flamelet model and the Interactive Eulerian Particle Flamelet model. Validation was carried out with data from the Sandia combustion vessel, by comparing computed and experimental data of pressure rise, heat release, lift-off length, flame structure and acetylene and formaldehyde distributions, in order to investigate the capability of the models to predict soot precursors. The simulations carried out using a single flamelet show that the RIF model cannot reproduce lift-off, predicting a flame which is attached to the injector tip. The most encouraging results have been obtained using the Eulerian Particle Flamelet model with flamelets created according to the injection time. These simulations are able to reproduce the flame propagation and a flame structure in rather good agreement with the real one. For this model the influence of ambient conditions on the results has been investigated in terms of initial vessel temperature, density and oxygen concentration.