A Numerical Study On The Process Of Cavitation And Gas-Liquid Two Phase Flows In Fuel Injectors

The injection performance of a fuel injector has substantial effects on the fuel-air mixture formation as well as on the combustion and emission characteristics of diesel engines, However, There are many factors affecting it's the injection and atomization behaviors of the injector. One of them is cavitation. Recently, the study on cavitation has become a research hotspot in the area of ICE.. The study of the internal flow inside the nozzle of the fuel injector is impeded by several factors, including the extremely small size of the nozzle, very high speed of the flow through the holes, the transient and highly turbulent behavior of the flow, and two-phase phenomena in the internal flow. Experimental study is very difficultly for a nozzle flow.Hence, this thesis studies the cavitation phenomena by numerical simulations with the CFD software-Fluent. The thesis starts with an overview of the cavitation theory, presents related knowledge about CFD to nozzle flow simulation. Then nozzle geometric models of; and relevant physical and mathematical submodels and related parameters are determined and presented. Finally, computational results are discussed and analyzed. Work completed in this thesis are mainly as follows:(1) The process of cavitation in a two-dimensional microchannel is numerically simulated. Effects on cavitation of the pressure difference between the inlet and outlet, the ratio of length to diameter, and the inlet corner radius of the microchannel are discussed.(2) The cavitation process in a real diesel nozzle, is computed and compared with the two-dimension microchannel.(3) Liquid jet flow injected into a cavity is simulated by taking into account of the cavitation effect, and compared with that without cavitation. Based on this, the essential influence of cavitation on the spray and atomization behavior of the jet is demonstrated.(4) The cavitation behavior in converging and diverging nozzles is numerically studied, the effect of the inlet to outlet area ratio is examined in detail.