An Empirical SI Combustion Model Using Laminar Burning Velocity Correlations

Predictive simulation models are needed in order to exploit the full benefits of 1-D engine simulation. Simulation model alterations such as cam phasing affect the gas composition and gas state in the cylinders and have an effect on the combustion. Modelling of these effects is particularly important when the engine is knock limited. A knock model, able to phase the combustion towards the knock limit, was previously developed by the authors. A major challenge in such knock models is to predict the pressure and temperature evolution in the end-gas accurately through an adequate combustion model. The Wiebe function is often used to model the combustion in SI engine simulations, owing to its ease of use and computational efficiency. The Wiebe function simply imposes a curve shape for the fuel burn rate and the parameters are easily determined from calculated heat release. Detailed models of turbulent combustion also exist which require more knowledge or assumptions about combustion chamber turbulence. The combustion model proposed in this paper uses existing correlations of laminar burning velocity to predict the parameters of the Wiebe function relative to a base operating condition. The model aims at predicting combustion at high load operation. Experimental and simulation data from a gasoline fuelled 4-cylinder turbo charged port injected spark ignition engine are used to correlate the Wiebe function parameters dependence on laminar burning velocity.