Study On The Matching Of HPCR Injection System And Diesel Engine Combustion Chamber

Diesel engine is a major trend of the development. Diesel with high thermal efficiency, and easy to implement exhaust-driven turbocharger, low fuel consumption, high torque and reliability, long life and other advantages is getting more attention from the manufacturers. As the growing awareness of the energy crisis and environmental issues, people put the economy and emissions to a much more important place.With increasingly stringent energy conservation and emissions regulations, diesel engine injection system with electronic control and high-pressure is put into use. And, at the same time, the necking-DI chamber became more popular. However, the unreasonable way of matching and employment will lead not only less effectively use of this kind of necking-combustion-chamber's features, but its performance deteriorated. Therefore, in order to make more effectively use of the structural characteristics and flow characteristics of the necking combustion chamber, to keep the power and economy unchanged (or basically unchanged), at the same time, to decrease the emissions of diesel engines effectively. It is necessary to study the matching optimization of the high-pressure common rail fuel injection system parameters and the structure of the combustion chamber shape, and that is a very important link in the development of DI diesel engine.Based on domestic high-speed High-Pressure Common Rail Direct Injection Diesel vehicles, this paper studied the impact of the structure of the Necking combustion chamber on the airflow characteristics of indoor air by the results of software simulation. At the same time, ground on the matching of injection characteristics and flow field, this paper studied the transient characteristics of the formation of mixture and its effect on the combustion process. Then by changing the parameters of the fuel injection system, the paper studied the impact of different matching of injection and airflow characteristics of indoor air on the velocity field, concentration and temperature fields on the combustion chamber. According to the study, people can find the way to optimize combustion chamber structure, toorganize air movement more effectively and to get the optimized matching of fuel injection system parameters. This paper is based on a actual topic. In the topic the engine with 2.8L displacement on SUV vehicle has been reconstructed to a engine with 2.5L displacement. The compression ratio and the cylinder diameter remain unchanged. The new engine has to meet the emissions requirements and keep up the power and economy. According to the requirement of the manufactory we designed the first 2.5L chamber (Type II) based on the original 2.8 L diesel engine combustion chamber. With the same compression ratio, in order to keep up the airflow characteristics of indoor air, we decreased the Necking-ratio and the depth of the combustion chamber. In addition, we designed another 2.5L chamber (type III) based on the Type II chamber by increased the Necking-ratio appropriately to analysis the impact of Necking-ratio on the airflow characteristics of indoor air and the process of mixture formation. Through the simulation of the three combustion chamber, including the 2.8L prototype (Type I), we analysis the impact of different combustion chamber structure on the space distribution of the airflow characteristics of indoor air, dynamic distribution, and when coupled with spray, the effects on velocity field, concentration and temperature fields on the combustion chamber. At the same time, based on the same combustion chamber, analysis the impact of different injection pressure and injection timing on the velocity field, the concentration and temperature fields. The results show that for the necking direct injection combustion chamber the deeper the pit is the more conducive it is to the formation of vortex, and can maintain a certain intensity of the vortex movement longer. But if there is no good match with the injection, not only can not get its superior features, but will deteriorate the engine performance. Similarly, only by increasing injection pressure to improve spray quality, with no good match with the airflow characteristics of indoor air, again the engine performance will not be optimized. With the same largest diameter of the combustion chamber, the premixed combustion can be inhibited by decreasing the necking-ratio. Increasing the injection pressure can improve not only the quality of the spray atomization, but also the air flow. As a result, it can promote the premixed combustion and diffusion combustion at the same time. Small injection advance angle can also inhibit the premixed combustion effectively. Therefore considered all the factors above, we can get further improvement of the diesel engine emission characteristics by the rational design of the combustion chamber structure and injection system parameters and the reasonable match of them, without the loss of power and economy. And this multi-parameter optimization matching is very meticulous and complex, there is the need for further in-depth study.