Analysis Of Fuel Injection System Cavitating Flow And Fuel Characteristics

Improvements in the fuel injection systems of internal combustion engines can substantially reduce the emission of harmful pollutants. Meanwhile, improve fuel economy and engine power. Fuel injection systems produce spray, which directly affects the combustion of the fuel, which in turn determines the production of pollutants. However, the details of this causal relationship remain unclear. The goal of research is to understand the flow inside fuel injector nozzles and the implications for the downstream spray.The paper began with a literature review of liquid jet breakup mechanism and nozzle internal flow which was helpful in identifying the relative importance of phenomena such as cavitation. Combined with experimental works done by the previous researchers, we used computational fluid dynamics (CFD) method to investigate the three dimensions cavitating flow inside the nozzles. Simulation results suggested that cavitation was likely occurring inside fuel injector nozzles. Next, different models were built to analyze the cause of cavitation. The result suggested that high grads of pressure drop near the nozzle entrance was responsible for the appearance of cavitation.Cavitation could affect nozzle internal flow dramatically, nevertheless it will impact downstream spray. So, the profiles of velocity and turbulence kinetic energy on nozzles exit were analyzed to implicate the downstream spray characteristics. The result indicated that with the appearance of cavitation the nozzle exit flow have higher turbulence kinetic energy and velocity. This research can provide reference for spray breakup models.Accompany with the potential energy crisis, the research on substitute fuels were carried out all over the world. Diesel engine was reported to be the most suitable engine to run these substitute fuels. To investigate the influence of fuel properties like density,viscosity and bulk modulus of elasticity on injection process, a common rail(CR) system numerical model was constructed. Simulation results revealed that in CR systems injection timing is not influenced by fluid bulk modulus of elasticity on diesel engines; density has an evident effect on injection rate; fluid viscosity only has a marginal influence on needle lift because the flow is turbulent almost immediately.