engleski

Development of a Stratified Fractal Combustion Model

Multi-zone combustion models of SI (spark-ignition) engines have a large potential in engineering applications because of their robustness and very low computational effort, compared with CFD (computational fluid dynamics) models. One of the multi-zone models is a fractal combustion model which is implemented in the AVL Boost software. The model divides the cylinder mixture during combustion into two separate zones: the burned and the unburned zone. The basic fractal combustion model defines the propagation of the flame front on the basis of the homogeneous state in the unburned zone. Because of this assumption the model is capable of simulating only homogeneous cylinder mixtures. Since SI engines that use stratified mixtures have been developed lately, the basic fractal combustion model is improved so that it can use stratified mixtures. In a stratified fractal combustion model the local state near the flame front is defined on the basis of the combustion progress. By using stratified profiles of the air equivalence ratio and/or of the combustion products in the cylinder, the extended model is able to capture the effects of mixture non-uniformity. These stratified profiles of the air equivalence ratio and/or of the combustion products can be obtained by using other softwares (e.g. CFD simulations), or they can be assumed. The performance of the new stratified fractal model is tested by calculations with assumed profiles. The results of the stratified fractal combustion model are compared with the results of the basic model. This analysis showed logical behavior of the improved combustion model.

AVL Boost; fractal model; simulation; stratified mixtures

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