| Through the development of internal combustion engine for many years, it gets a wide application. With these problems of the energy shortage and environmental pollution, people have begun to put forward a variety of ways to improve the quality of combustion, in order to advance the dynamic, economical and emission performance. Particularly, four-valve diesel engines have got the development in the research and application widely. It makes to change the number, structure and location of the intake port for the traditional two-valve diesel engine, to get many particular advantages which the traditional two-valve diesel engine can't have. Four-valve diesel engine can increase the valve area, add the intake charge, reduce pumping loss, make the combustion chamber and fuel injector on the cylinder head located in the center of cylinder, improve the symmetrical distribution of the intake swirl and the fuel oil atomization, speed up the formation of the mixture, enhance the cooling conditions of the injector and piston, at the same time achieve the variable swirl in the different speed, and make the combustion efficient and emission clean. From the view of development, it has become a necessary trend of development that multi-valve engine will replace the traditional two-valve engine.Based on the characteristics of the actual model, the paper drew three-dimensional model of 135 diesel by the UG soft, did the design of the four-valve diesel with two spiral inlets,four-valve diesel with a spiral inlet and a tangential inlet and two-valve diesel with only a spiral inlet, did the numerical simulation for in-cylinder fluid intake; compression, sprayed and combustion process by Star-CD computational fluid soft; gained the in-cylinder flow information in every process, time and angle and compared three diesels; obtained that the diesel with two spiral inlets occupied absolute advantages in the flow and combustion course. Its flow is large-scale in cylinder; it owns strong swirl and tumble. These are helpful to the atomization of fuel and formation of mixture. In analyzing the effects of combustion, the advantage of this diesel is obvious; compared with the other two types of diesels, the beginning time of combustion is earliest, ignition delay is shortest, the average temperature and pressure is highest, the combustion is most concentrated, the fire range of in-cylinder is widest, combustion effect is most wonderful and working ability is strongest. During analyzing the effects of the fuel atomization, in the initial stage of fuel injection, the fuel evaporated mass and the fuel evaporated rate are highest, the sauter mean diameter is smallest relatively, in the latter period of fuel injection and the period of diffuse combustion, the fuel evaporated mass and the fuel evaporated rate are smoothest relatively, and at the end of combustion, the remainder of fuel evaporated mass comes to zero.To sum up, the paper compares four-valve diesel with two spiral inlets to four-valve diesel with a spiral inlet and a tangential inlet and two-valve diesel with only a spiral inlet which are different inlet structures, and it proves that the diesel with two spiral inlets heightens the quality of combustion adequately, and enhances the dynamic and economical performance with the comparison of the traditional two-valve diesel. It provides a theoretical basis for the further study of different inlet structures and four-valve technology. |
