Numerical Study On The Working Process Of Direct Injection Spark-Chamber Gasoline Engine

With the high thermal efficiency, specific power and excellent reliability, internal combustion engines become the most popular power machinery in the world since its invention. It is widely used in ships, engineering machinery and automotive fields. With the increasingly serious energy and environmental issues, emission regulations for vehicles are more stringent in recent years; the development of engines faces a severe challenge. Compared with the port fuel inject (PFI) engine, the gasoline direct inject (GDI) engine performances great advantages in fuel economy, cold start emissions, transient response speed and many other parts. GDI engine becomes major and popular research topic of gasoline engine. The ignition reliability of stratified lean burn GDI engine has always been one of the main issues. Therefore, the concept of Direct-Injection Spark-Chamber (DISC) gasoline combustion system is advanced. A DISC prototype engine is rebuilt from a GDI engine, a spark chamber is set on the cylinder head, the spark is disposed in this chamber, and the nozzle can be disposed in the spark chamber or main chamber. Appropriate fuel injection strategies and the flow distribution in cylinder are used to keep the mixture inside the spark-chamber at the range within which the mixture is easy to be ignited, and the mixture in main chamber is lean. The stratified lean burn is achieved. The numerical study on the working process of this engine is complicated and the feasibility is validated.In order to study the working process in cylinder, a new 3-D model is created with the software of CATIA,1-D boundary condition is got from the simulation results with software of AVL Boost, and then the 3-D numerical simulation on the working process of this DISC engine is complicated with 3-D CFD software. Three typical work conditions are calculated, including the flow movement process, spray development process, mixture gas formation process and the combustion process in cylinder. The effects of using four different inject times and different spark chamber shapes to the working process in cylinder are analyzed. The differences of the turbulent kinetic energy's distribution and squish velocity at connect channel between three work conditions is compared, the effects of different operate speeds to the working process is explored.From the simulation results, the following conclusions can be made:ideal mixture gas distribution can be got at all three typical work conditions of this system, the mixture stratified well; around the spark plug the mixture with suitable equivalence ratio can be ignited stably in large range of crank angle. This indicated that the system has a wide ignition time sequence, great ignition reliability and combustion stability; the engine operated stably at three typical work conditions. The feasibility of the DISC system in different work conditions is verified. The combustion processes in cylinder of three typical work conditions are all lean burn. High temperature region is extremely fully burnt, without remaining oxygen; the temperature of the oxygen-rich zone is lower than 1500 K, reducing the generation of thermal NOχ. With a high compression ratio and lean combustion mode with large air-fuel ratio, the supply level of the circulating oil amount is reduced and the fuel economy is improved.