A Diesel Engine Cycle Model for Prediction of Performance and Pollutants Emission

Abstract

In this article, a mathematical model is developed for prediction of important performance parameters and emission of major pollutants from a Direct Injection (DI) diesel engine. The model has ability for simulating performance and emission of four-stroke DI diesel engines by taking into account the closed cycle (compression stroke, combustion process and expansion stroke). During the whole cycle of events, heat transfer from the cylinder charge to the combustion chamber walls is considered. Since accurate prediction of thermodynamic properties of the cylinder charge at the injection timing has obvious effect on ignition delay period, so in this study during compression stroke, cylinder charge is considered as actual working fluid. By developing a fuel injection system (FIS) submodel, variation of injection pressure during the injection period is considered. Also in this code, time period of ignition delay is predicted by considering the physical and chemical processes. The combustion submodel is a quasidimensional phenomenological model and is based on well-know Integral Multi Zone Combustion Modelling (IMZCM) concept. It takes into account on a zonal basis, the details of fuel spray formation, air-fuel mixing and air swirl. The emission submodel uses the chemical equilibrium as well as the governing kinetics rules for calculation of pollutants' formation such as nitrogen oxides (NOx) and soot particles. For calculation of NOx formation rate, extended Zeldovich mechanism has been used. For evaluating soot particles' concentration, the amount of net soot is calculated by considering the difference between the rates of soot formation and its oxidation inside the zones. In addition to prediction of exhaust concentrations of the above pollutants, the code has the potential of evaluating the incylinder spatial and temporal concentration distribution of pollutants. Also in this paper, capability of the model in accurate predicting of important performance parameters such as imep and ηthi is demonstrated. The results obtained from the model are compared with the experimental conditions of the typical medium and high speed DI diesel engines. The comparison shows that, there exist good agreement between the predicted and the experimental results.