Numerical Simulation Of Effects Of Multi-injection On Hydrogen Fueled Engines With Port Fuel Injection

Humanity has been in trouble of global energy crisis and environmental problems,especially the environmental problems of our country.One of the main factors is emissions from fossil fuel combustion of the traditional vehicle engine.So trying to seek for clean alternative fuels for traditional engines has become a hotspot.Hydrogen has been being researched by researchers,because it can solve energy crisis and environmental problems at the same time in all of the alternative fuels.As to the application of hydrogen,even though hydrogen engine with external hybrid has a simple structure and is easy to implement,it has some shortcomings,such as occurrence of backfire and preignition,low power density and so on.For the reason of low power density under condition of external hybrid,the mainstream view in academia is that hydrogen has the property of low density and high diffusivity.It can take up some space in cylinder,which will cause the decrease of engine charge coefficient.Finally,the engine's power declines.This paper,from the perspective of effects of hydrogen jet on the flow state in the intake pipe,the problem about low power density were studied based on numerical simulation with AVL Fire as a tool.The study finds that there is a contradiction existing in the engine at medium and low speeds.The contradiction is between backflow of fresh air at the middle period of intake and increasing of hydrogen residues in intake port at the late period of intake.In order to solve both contradictions mentioned above,this article proposed the strategy of multi-injection.After the strategy was studied,we find that four-times injection has not solved the problem of backflow of fresh air effectively at low speed since the backflow was so severe in the middle period of intake.Reversly,it resulted in the decline of H2 mass in cylinder.In contrast,as the speed increased,the strategy of multi-injection could alleviate,to some extent,or even solve the problem of backflow of fresh air in the middle period of intake.The mass of both fresh air and H2 in cylinder increased.So the maximum cylinder combustion temperature and pressure were improved.Further more,the power of the engine was enhanced while the emission of NO deteriorated.Also,the strategy of multi-injection could improve the homogeneity of cylinder mixture,which could shorten the period of rapid combustion and increase indicated thermal efficiency.