Study On The Influence Of Spray Unevenness On The Mixture Formation Of Aviation Kerosene Engine

Aviation kerosene was widely used in spark ignition piston aviation engines,which is due to the importance of fuel safety and the characteristics of aviation kerosene,such as higher flash point,lower saturated vapor pressure,and volatilization difficulty.However,many problems follow,such as bad quality of fuel mixture formation,combustion instability and increase of detonation tendency.Most scholars in the past only focused on the effect of spray SMD on the mixture formation,and the spray unevenness was also one of the important factors of it.Therefore,under different working conditions,different fuel temperature and excess air coefficient,the combined effects of spray unevenness and SMD on the mixture formation were studied,and the influence degree of spray unevenness on the mixture formation was analyzed.For this purpose,the one-dimensional simulation model of engine was built by GT-power software and the three-dimensional simulation model of engine cylinder was built by AVL-Fire software.Then,the models were verified by engine bench and visualizing spray experiment results.In order to ensure the accuracy of simulation calculation,the grid independence was verified by simulation results of varied grid generation forms.A new definition of spray unevenness was presented in this paper.According to the range of spray unevenness,obtained by experiment,the droplet diameter distribution scheme in the simulation example was designed.In the simulation calculation,the three parameters of spray SMD,fuel temperature and excess air coefficient were changed with spray unevenness under rated working conditions and cold start conditions.According to the above calculation results,the comprehensive influence law of spray unevenness on the mixture formation was analyzed.The results show that the spray unevenness is between 1.5 and 2.3,when using air-assisted direct injection system to spray aviation kerosene.At rated working condition,with the increase of spray unevenness,the number of large diameter droplets formed in the cylinder at ignition time increases too.And these large diameter fuel droplets often appear near the spark and the cylinder edge,which will cause the decrease of ignition quality and the increase of possibility of detonation.Also with the increase of spray unevenness,the evaporation of fuel decreases and the SMD of non-evaporation fuel increases at ignition time.With the increase of spray SMD,the bad effects of the increase of the spray unevenness on the fuel mixture formation gradually increase.On the contrary,with the increase of spray temperature,the bad effects of the increase of the spray unevenness on the fuel mixture formation gradually decrease.When the spray SMD exceeds 10μm,reducing the spray unevenness is more effective than heating fuel to optimize fuel mixture formation.When the spray SMD exceeds 15μm and fuel is heated,reducing the spray unevenness is more effective than reducing the spray SMD to optimize fuel mixture formation.At cold start condition,the bad effects of the increase of the spray unevenness on the fuel mixture formation almost have the same law as rated working condition.In addition,there is no obvious relevance between the bad effects of the increase of the spray unevenness on the fuel mixture formation and different excess air coefficient.When the spray SMD is bigger,reducing the spray unevenness is more effective than increasing fuel injection quantity to optimize fuel mixture formation.In other words,when the spray SMD is bigger,the cold start performance of aviation engines can be optimized and the fuel consumption can be reduced by reducing the spray unevenness.