Modeling of HCCI Combustion by One Step Reaction Function: In View of Assisting the Optimization of Engine Management System 2007-24-0033

Homogeneous charge compression ignition (HCCI) is one of the alternatives to reduce significantly diesel engine emissions for the future emissions regulations. This new alternative combustion process is mainly controlled by chemical kinetics, unlike conventional combustion in internal combustion engines. To satisfy the different modes of operation, the tuning of HCCI engines requires a large number of tests which are time-consuming and very expensive. To reduce the number of tests, a model with a very short computational time to simulate the engine in the whole operating range is needed; therefore the goal of this study is to provide the engine manufacturers with a simple physical combustion model to assist engine tuning and engine management system optimization, with the aim of predicting in-cylinder pressure evolutions and mean effective pressure (IMEP).

The proposed model is reduced to two state variables: the temperature and the mass fraction of burning fuel in the combustion chamber. The chemistry is modeled by a global degradation reaction where the reaction rate coefficient, usually modeled through the Arrhenius law is driven in this approach by a global function Ω(T). This global function takes into account the slow dynamic of the cool flame and the fast dynamic of the main ignition and the transition between the two stages. A drawback of the global approach is the introduction of some new parameters which need to be correlated to give reliable results; this has required an important and large parametric study to calibrate the reaction rate coefficient. The proposed model is then autonomous, meaning that the model parameters are function of the engine operating conditions only.

The results show that this type of model can be useful to describe the ignition delay time of HCCI combustion and the rate of heat release, with very short computational times around two seconds. The model has been compared to the model including reduced chemical mechanism developed previously and to Renault engine experimental data. This comparison shows that the model gives reasonable accuracy in terms of in-cylinder pressure and IMEP with very short computation time.