Numerical Simulation of Film Thickness Formation in a PFI Engine Under Motoring Conditions

Due to increased concern about emission, every source responsible for it should be eliminated or its influence reduced. In this respect the film formation over the wall region of a engine cylinder is analysed to understand the emission under adiabatic flow condition. The film on the wall starts forming when the air fuel mixture reaches the saturation temperature. In this paper a pent roof four valve Siamese intake port gasoline engine is selected and investigated under motoring condition accounting for cold start principle through single point Port Fuel Injection(PFI). About 46 mg of liquid fuel is injected through two injectors which are placed at the end of divided intake port of Siamese type. The injectors are angled about 20o w.r.t. centre vertical plane of Siamese intake port and 60o w.r.t. Horizontal plane of fire deck zone. The thickness of film formed by fuel droplets from the injector is gradually increased around the wall regions of the engine cylinder. When PFI system is used, the liquid film formation over the region of valve stem, valve face, intake port, dome, cylinder liner and piston top were more pronounced than the direct injection. The accumulation of film mass is more over the region of cylinder dome and port while compared to other regions inside and outside the cylinder. The cylinder dome region and port region are accounted about 6 mg and 12 mg respectively of film mass accumulation. From the total percentage of fuel injection, only 33 percentage of liquid fuel is evaporated and ready to mix with air to form charge for combustion. This shows that there is more chance of miss fire during cold start due to the influences of liquid film. The port region has 0.1mm thickness of film compared with other regions. It affects the quality of air fuel mixture for the next cycle and tends to affect combustion stability. Also it leads to soot formation inside the cylinder.