Two-Zone Model for Combustion and NOx Formation in Stratified Charge Operated Direct Injection Engines

The Direct Injection (DI) engines, both Diesel and Spark Ignited, comparing with the other types of engines have got many advantages; for instance: higher total efficiency, lower fuel consumption, lower exhaust toxicity etc. Above reasons make these kind of engines as the current powering source of automotive vehicles and machines, and it seems it will be so for the few next decades. However, because of operating with high number of air excess (lambda > 1), they can emit nitric oxides quite much, what becomes the environment problem, all the more the TWC catalytic reduction of NO(X) in exhaust system at lean combustion is rather difficult. Therefore, the primary method of NO(X) emission reduction is to prevent NO(X) formation during combustion process. The rate of combustion in direct injection engines depends on many factors. But the fuel injection process influences combustion fundamentally; a lot of parameters (dQ/dt, dT/dt, dp/dt, as well NO(X) emission) depend on fuel injection rate and fuel distribution in the combustion chamber. Optimization of fuel systems and injection strategy for ecological and operational engine parameters simultaneous improving is very difficult and expensive. This process calls for doing many experiments and research. In consequence, the final result may take too much time and funds. Instead, numerical simulation allows limiting the investigation expenses, but never completely excludes doing research, of course. So, having the knowledge received from computer simulation on relationship between fuel injection rate and NO(X) exhaust emission in DI combustion engines, can be very helpful. For this reasons, the authors have worked out the model of combustion and NO(X) formation, which uses,the fuel injection rate as the main input data. For the NO(X) formation model, the thermal Zeldovitch mechanism is applied. The model makes possible testing of correlation between fuel injection rate and many combustion parameters and NO(X) emission value. The paper presents the outline of the model and some calculation results.