Study On Split Injection To Strengthen The Combustion Performance Of Diesel Engine

With the depletion of oil resources, more and more attention is paid to further optimization of the combustion process, power performance and fuel consumption of diesel engine. Split injection technology provides a good way to improve the emission of diesel engine and a large amount of studies show that NOx and Soot in diesel engine could be effectively controlled by using fuel split injection. However few research show how split injection influence the power performance of diesel engine. This article mainly focus on power performance of diesel engine and make deep study on the influence of split injection together with swirl ration on the fuel air mixing, combustion process of diesel engine.First of all, a common rail fuel injection system is built and the characteristics of this injection system were studied experimentally. Then on the 1132 Z single cylinder diesel engine test bench, experiment research is carried out to explore the influence of ratio of pilot injection, interval between pilot injection and main injection and swirl on the performance of diesel engine. The results show that, compared with the traditional singular injection, the power performance and fuel consumption of diesel engine are improved by using split injection. Meanwhile, with swirl in-cylinder, power performance of diesel engine becomes even better, because the heat release rate of main injection is accelerated.Secondly, by using visioscope system together with high speed photography, the combustion process of split injection is studied on 1132 Z single cylinder diesel engine test bench. Flame temperature and KL factor is achieved by using two color method. The results shows that, by using split injection, combustion duration and soot emission are both reduced. When there is swirl in cylinder, the flame is deflected and fuel air mixing is accelerated.Third, In order to improve the precision of the simulation research by using split injection, spray and combustion model of diesel engine is established, and the verification and validation work is carried out. Free jet results from experiment are used to help calibrate the parameters in spray and evaporation models. A good agreement of liquid phase and gas phase spray characteristic is then achieved between experiment and simulation resusults. Then, the ECFM-3Z combustion model is proved that it is suitable for calculation of diesel engine when using split injection. Then paremeters in both spray, evaporation and combustion models are fixed for the following simulation of split injection and accuracy of simulation is improved.Fourth, simulation research is carried out to explore the influence of ratio of pilot injection, interval between pilot injection, main injection and swirl on the performance of diesel engine. And mechanism of influence on fuel distribution, fuel air mixing progress and combustion process by using split injection and swirl are both analyzed. Then the matching relationship among number of injector holes, injection duration of pilot injection, interval between poilot injection and main injection and swirl ration is put forward.Finally, Research shows that there is a good matching relationship between split injection parameters and swirl ratio, which means with reasonable split injection parameters and swirl ratio the main injection can make full use of the thermo atmosphere of the pilot injection without restricted by it. By this means, the fuel air mixing and combustion process of diesel engine will be improved and better power performance, thermal efficiency, as well as fuel consumption are achieved.