Study On In-Cylinder Flow Field Of Gasoline Engine By Particle Image Velocimetry(PIV)Technology

The air motion in cylinder of internal combustion engine has great effect on the form and combustion course of the mixed gas. It affects engine performances of power, fuel economy and emission. PIV(Particle Image Velocimetry)is a two dimension velocity field measurement technology with no interference, instantaneous measure on whole field, collecting and handling about data synchronously. The in-cylinder flow field of a four-valve gasoline engine is studied by PIV technology in order to improve engine performance.A test rig of internal flow field of engine is improved in the thesis to satisfy request of experiment, including improving the drive system of optics engine, developing an electronic control system which can control PIV to shoot continuously at predetermined crank angles, optimizing the parameters of experiment and so on. The paper studies perfectly processing method about data for in-cylinder flow fields. Because the fluid motion in the cylinder of the engine is the turbulent flow structure, the sample average technique is used to study the whole structure of the field, which reduces the influence of the cycle's discrepancy. Bases on the measured velocity vector data, the velocity vector streamline diagram, average velocity graph, turbulent flow intensity contour plot for time, turbulent flow intensity graph for space, swirl ratio, tumble ratio and so on are used to analyze the flow fields structures and the evolution processes. They provide the basis for quantitative analysis of in-cylinder flow field of gasoline engine.In the paper PIV was used to measure the flow field in the cylinder at intake and compression stroke,including the flow field of different cross section at different speed and two vertical planes of the cylinder and valve center at the same speed. The results show that there is no large scale swirl vortex in the cylinder with two intake valves working, while a large scale swirl vortex can be observed with one intake valve working; tumble flow is very obvious, produced at the stage of intake stroke, experiencing from weak to strong and from two vortex to a large scale tumble vortex ; tumble vortex strengthen with one intake valve working than two, and tumble vortex in the valve center plane is more obvious than the cylinder center paper; the turbulent flow intensity both for time and space have great direction and take the direction of Y as predomination; the absolute turbulent flow intensity curve varies slowly with crank angle, while relative turbulent flow intensity curve fluctuate bigger and it is peak...