Simulation Study Of Flash Boiling Spray Characteristics And Combustion And Emission Effects

Energy security and environmental pollution at home and abroad are related to the stability and development of world peace.Direct injection gasoline engine has obviously improve fuel economy,reduce emissions,but because of the GDI engine working medium mixing time is shorter,there exists a particle emission and combustion problems such as uneven,so the atomization of fuel quality of GDI engine particulate emissions and combustion efficiency has the important influence,flash boiling is improved fuel atomization quality is one of the effective means.In this paper,a detailed simulation study was conducted on the characteristics of flash boiling spray and its influence on the combustion and emissions of a direct injection gasoline engine.According to the existing test data of constant volume bomb in Sandia National Laboratory of the United States,a constant volume bomb simulation model of Spray G was built to simulate the spray morphology and atomization effect of flash boiling spray.The collapse of porous flash spraying,mixing of different proportions of fuel and flow in the hole of flash spraying were studied.For the internal combustion chamber simulation of internal combustion engine,an EA111 engine was used as the original engine to build a combustion chamber model.The engine speed was 2200r/min and the effective torque was118N·m at a working point.The fuel temperature was changed to compare the combustion characteristics and emission characteristics of flash boiling spray and cold spray.The conclusions are as follows:1.The dimensionless superheat composed of environmental pressure and fuel temperature has the most important influence on the spray morphology and crushing degree of flash boiling spray,but has little influence on the superheat degree of cold spray;Under the same superheat,the spray morphology and the degree of breakage will be slightly different due to the different environmental pressure.Ambient temperature also has a certain degree of influence on spray morphology and fragmentation degree.2.The collapse phenomenon of flash boiling spray is mainly caused by the interference between oil bundles.For flash boiling spray,different number of spray holes,injection direction and spacing of spray holes will affect the distance between oil bundles,thus affecting the collapse phenomenon of spray.3.Mixing low boiling point fuel with high boiling point fuel will promote the degree of spray breakage and change the spray morphology.On the whole,the atomization effect of the spray is improved.The promoting effect of the cold spray is weaker than that of the transition flash-boiling and intense flash-boiling,and it becomes more intense with the increase of the proportion of the low boiling point fuel,until the spray form of pure low boiling point fuel changes significantly.4.The hole wall roughness for cold spray cavitation phenomenon has a certain role in promoting,can provide more venues for cavitation phenomenon,but for the flash boiling spray instead of its effect on the velocity of down hole cavitation and boiling phenomena occur,and low velocity will reduce traffic,this will make the liquid into the total mass of the gas phase down;For different orifice lengths,the longer orifice of cold spray can promote the cavitation phenomenon,while for flash boiling spray,the longer orifice will lead to the low flow rate and inhibit the flash boiling phenomenon in the orifice.5.For cold state spray and transient flash boiling spray,increasing fuel temperature can enhance the breaking and evaporation intensity of spray droplets,so the combustion effect will become stronger with the increase of fuel temperature,and the peak cylinder pressure will increase.Meanwhile,the soot generation quality will decrease due to the more uniform distribution of the mixture.However,in some transient flash boiling conditions,the droplet movement in the cylinder changes due to the change of droplet diameter,resulting in poor mixing effect.Fuel for intense flash boiling spray,but too high temperature will lead to the spray cone Angle grows wider,the interference between spray are strengthened,destroyed the spray jet direction of originally,strong spray may result in uneven mixture formation collapse phenomenon,at the same time,high fuel temperature leads to the decrease of the air inflow,cause severe flash boiling spray combustion and emission effect to a certain extent.