Research On The Wetted Fuel Film In Electrical Controlled Injection Gasoline Engine During Cold Starting

In SI engines with port injection system, the injected fuel spray adheres surely on the port wall and the inlet valve. Consequently, the spray-wall interaction process leads to the generation of unburned hydrocarbons and uncontrollable mixture formation. With the support from National Nature Science Fund, this paper includes basic research of the influence factor of the wall-wetted fuel film after spray impingement with a flat wall.Laser Induced Fluorescent (LIF) was used to measure the thickness of fuel film at different location. Film image was obtained by the use of High Speed Camera; film area was achieved through image process. The film area ( f ) and the thickness (h) was quantitatively measured as a function of the impingement distance from the injector to the wall ( Z w), the impingement angle against the wall (α) and the inject duration ( t inj).The experiment result indicates that:(1) With the increase of Z w, there will be smaller quantity of fuel on the wall.(2) The increase of t inj means larger quantity of wall wetted fuel.(3) Whenαdecline, the wall wetted film is easily to evaporate.(4) Film area increase velocity was discussed by the help of a non-dimensional time. The results show that, the film area will not change after non-dimensional time reaches 1.5.In general, the flow pattern in intake manifolds is extremely complex. A liquid jet enters the intake where it atomizes into droplets due to the forces of the air flow. The transport of fuel by air into the cylinder occurs as vapor, droplets and liquid streams from the fuel film. A wind tunnel was developed to simulate the intake of the gasoline engine. Spray impinges with the bottom wall of the tunnel to form fuel film. The area and thickness of film was researched at different air velocity.The experimental result shows that:(1) With the increment of gas velocity, the thickness of fuel film will decrease;(2) The area will firstly decrease and then increase with the increase of gas velocity;(3) When the gas velocity reaches 14.43m/s, the spray structure will be affected obviously, area, thickness and the location of film will change significantly.Further more, spray-wall interaction sub-model was modified for application to SI engines based on Fluent. In this sub-model, fuel film formation due to the droplet-droplet interaction near the wall and droplet-wall film interaction, fuel film transport, droplet interaction film breakup, and the velocity and direction of dispersing splashing droplets were considered.Then, the spray development and the fuel film profile formed on the wall were calculated and compared with experimental results. Several conclusions are made based on the computational results.The film area is easily to spread at small injection angle. When the roughness of the flat wall increases, there will be smaller quantity of wetted fuel. Higher wall temperature will results decrease of thickness of wall wetted fuel film.