Numerical Simulation And Experiment Research For Reducing Exhaust Emission Of DI Diesel Engines

With the country exhaust emission standards increasingly strict, DI diesel must be improved by using new advanced technology. The aim of this paper is reducing NOx and particles emission of DI diesel to meet Europe II standards.Based on changing oil pump to increase spraying pressure, we designed and developed several kinds of combustion chamber shapes and nozzles, which are main factors for influencing performance and exhaust emission level of DI diesel. Several kinds of combustion chambers were developed and designed at the situation of constant compression ratio and volume, according to the theory of combustion chamber design. Their process of combustion and spraying were contrasted by numerical computation at the same condition. The results show that it is easy to form squashing flow in the combustion chamber with a center raise. And the transition radii of the impinging point of fuel at the combustion chamber wall, should be designed to favorable diffusion of the fuel in order to accelerate mixing with air after impinging wall. Through using numerical simulation method, we simulated diesel combustion process for several different kinds of combustion chamber shape and different parameters nozzles, and implemented prediction of exhaust emission formation trend. It led to reducing times of experiment , human and material costs. This paper shows flow field in-cylinder, spraying evolution and space distribution, temperature field in detail, by simulating process of gas phase flow, spraying and combustion for DI diesel. And it mainly analyzes spraying flow evolution process, characteristic of turbulence and vortex, and exhaust emission formation. Also through comparing with experimental results, computational models and parameters are proved to be reasonable. The main factors, such as shape of combustion chamber , diameter and number of holes of injector, spraying angle, fueling advance angle, which influence the performance and exhaust emission level of DI diesel, are analyzed and researched detailedly by intergrating theory analysis, numerical computation and experiment.