Novel regression models for wiebe parameters aimed at 0D combustion simulation in spark ignition engines

In the present work a novel predictive Wiebe-Based combustion Model (WBM) is proposed for simulation of the combustion process in a normally aspirated 1.6 L spark ignition (SI) engine. Unlike other approaches presented in literature, the novelty consists of: the considered set of Wiebe parameters, that is the angle at 50% of burned fuel, the combustion duration between 10% and 90% of burned fuel, and the form factor m; the nonlinear feature of the used correlations; the set of the involved engine variables, including particularly the laminar burning speed of the air/fuel mixture at combustion start. Based on a wide experimental database a Turbulent entrainment Combustion Model (TCM) is also set up, validated and embedded in a 1D simulation model of the engine. The parameters of the Wiebe function fitting the Mass Burned Fraction (MBF) development are estimated for each engine operating condition and then correlated to main engine variables. To assess to what extent the simpler WBM can be used in place of the TCM, simulations of the validated 1D engine model were carried out with both WBM and TCM and their performances compared in a wide range of engine operating conditions in terms of Brake Mean Effective Pressure (BMEP), Brake Specific Fuel Consumption (BSFC) and Carbon monoxide concentration (CO).