Reaserch On QHCCI (Quasi-Homogeneous Charge Compression Ignition) Combustion System

There are two serious problems that human beings have to face--one is pollution and the other is energy crisis. The two problems have extremely close relation with internal combustion engine. The analyses of recent research on internal combustion engine shows that lean burn in the gasoline engine and homogeneous combustion in diesel engine are the important focus of the research on internal combustion engine.An indirect injection diesel engine typed N485 was reconstructed into a direct injection engine and the gasoline injection equipment was installed in my research. An accelerator pick up was used to determine the quality of gasoline and the sensor was scaled. The control/measure system can control gasoline injection and signal measurement/analysis at same time. The static and dynamic flow rate of the gasoline injector ware tested.The experimental research on QHCCI(Quasi-Homogeneous Charge Compression Ignition) was made first by the author based on this reconstructed 4 cylinders direct injection diesel engine. The effects of gasoline injection timing on the engine were tested. The test result shows that the engine performance was not effected significantly if the injectors ware installed away from intake port in the manifold. The author adjusted the injection pressure. The test result shows that the engine performance was advanced slightly when the injection pressure was increased.The test result shows that the stability of the diesel delivery at small quality injection is very important for the performance of QHCCI combustion system. The uniform of fuel delivery between cylinders was extremely important. Decreasing the piston diameter of the pump can improve the stability. Adjusting the pump accurately was very important for the equality of diesel delivery. The uniform of the injectors was also important.Because the spacial ignition method, the QHCCI system have not significant ignition limit under the test condition. But the efficiency of combustion was low when the lambda of the pre-mixture is bigger than 3.0. Because there ware no throttle in the intake system, the engine performance under low load is deteriorated in QHCCI combustion mood.QHCCI combustion mood decreases the smoke and NO simultaneously. The results of 13-mode cycle test show that QHCCI combustion can reduce the PM and NO, but the HC/CO increase obviously simultaneously.The optimization for multi-target in multi-condition was first used to treat the test result. This method is instructive for the adjustment of the engine. Based on theoptimization the advanced performance was gained in the 13-mode cycle test by different injection timing for different condition.The author made a quasi-dimensional combustion model;which combines the diffusion combustion and pre-mixed combustion skillfully. The modeling results consisted with the experiment. The modeling gave a reasonable explanation for the experiment. The modeling discovered the reason of too high exhausted HC is that the flame hardly propagates to the end quench area. This could give an improving method of the combustion chamber in theory.After comparing different methods of knock detection;a method that utilizes cubic splint fit differentiator was used successfully to detect knock. The knocking mechanism of QHCCI was analyzed first time by the author. The knock is caused mostly by too high combustion speed for too much pilot fuel and too rich pre-mixture or by too close to the dead center position of combustion for the too early injection of pilot fuel. In order to decrease the knock trend;the diesel injection timing was adjusted. The test result shows that the knock tendency is decreased by delaying the injection timing at a proper extent.