Numerical simulation of combustion in premixed SI engines using fractal flame models

Multidimensional computations of homogeneous charge spark ignition engines were made with the KIVA II code. Combustion was simulated using the Fractal Flame Model of Zhao [ 5 ]. The original code was modified to obtain better calculations of heat transfer and to take into account the mass flow in the crevices. The predictions were compared with measurements carried out on a CFR engine. The tests were carried out in stoichiometric condition with isooctane. Compression ratio, ignition timing and EGR level were selected as test parameters. The global agreement between calculations and experiments was evaluated on the basis of heat release, indicated pressure patterns and pollutants measurements. For the lower compression ratio (7.7) the predictions of pressure cycle generally were in good agreement with experiments. However the empirical constant used in this condition cannot be used at higher compression ratio to obtain acceptable predictions of the pressure cycle. The calculations generally over-estimate NOx. Moreover the model is not able to predict correctly HC and CO levels in the exhaust.