Research On Combustion Characteristics Of Aviation Kerosene Engine Under Heavy Load Based On Injection Strategies

Piston-type aviation kerosene engine because of its high fuel viscosity,difficult to atomize,low octane number and saturated vapor pressure and other characteristics make it poor combustion stability under heavy load conditions,difficult to increase power output and knock tendency is difficult to control and therefore difficult to meet aviation aircraft take-off performance requirements.In response to these problems,this paper is based on a self-developed low-pressure air-assisted injection four-stroke aviation kerosene engine,based on different fuel injection strategies for its high-load combustion and power characteristics,Carrying out relevant experimental research,providing important reference value for future aviation kerosene engine combustion and performance development.In this paper,the DOE(Design of Experiment)method is used to investigate the coordinated control of multiple low-pressure air-assisted injection control parameters such as jet pulse width,jet pressure,fuel-air interval,and secondary injection.At the same time,the low-pressure air-assisted injection strategy is innovated and proposed synchronous injection strategy,the combustion and power characteristics of its heavy load operating conditions are tested in turn,and finally the composite injection strategy is adopted to control and analyze the combustion and knock characteristics of the aviation kerosene engine.The test results show that as the jet pulse width gradually increases,the combustion speed gradually increases,and the combustion quality gradually increases,and when the jet pulse width is greater than 4ms,its continued increase will gradually weaken the effect of improving the combustion performance of the engine.As the jet pressure gradually increases,the combustion quality first increases and then decreases and there is an optimal jet pressure of 650 k Pa,which makes the combustion quality the best,the cycle fluctuation rate COV(Coefficient of Variation)is the lowest,the power is the strongest,and the exhaust temperature is the lowest.The coordinated control of jet pressure and jet pulse width can further improve the overall performance of the engine compared to the separate control of the two.When the fuel-air interval increases from0.5ms to 2.5ms,the COV first decreases and then increases,and the power and combustion quality show a trend of first increasing and then decreasing.The best fuelair interval is 1.5ms.At this time,both the first and second atomization of the fuel can be used.The greatest advantage leads to the best engine combustion performance.Through the coordinated control of the fuel-air interval and jet pressure,it is found that the best fuel-air interval is 1.0ms under the lower jet pressure,and the best fuel-air interval is 2.5ms under the higher jet pressure.When the jet pressure is 600～700k Pa,the secondary injection and jet pressure coordinated control can further improve the combustion quality,and the optimal jet pressure is increased to 700 k Pa.The fuel-air synchronous injection strategy because the fuel after the first atomization is directly injected into the high-speed compressed air flow,the kinetic energy transfer between the fuel and the compressed air is increased,and the carrying and breaking effects of the compressed air on the fuel droplets are strengthened,so that the fuel atomization quality and atomization uniformity are correspondingly improved relative to the fuel-air interval injection strategy,which has further advantages in improving engine power and combustion stability.The test results of the compound injection strategy show that with the continuous decrease of the compound injection ratio β,the combustion speed first increases and then decreases,and there is an optimal β of 1:1,which makes the quality of the mixture formation in the cylinder and the combustion quality the best.The EOIT is gradually approaching the compression top dead center at the end of the internal direct injection,and the combustion speed first increases and then decreases.The best EOIT is 130°CA BTDC,which makes the COV the lowest and the power performance the best.The 3D spectrum map frequency domain analysis method is used to control and analyze the engine knock combustion.The results show that the knock characteristic frequency band of the engine under heavy load conditions is 3～19k Hz,and the abnormal heat release in this frequency band is made by adjusting β.The phenomenon is controlled,and the effect of suppressing knocking is achieved to a certain extent,and there is an optimal β of 2:3 to make the knocking tendency the lowest,and the knocking index KF is the smallest.Adjust the EOIT closer to the compression top dead center,KF first decreases and then increases,and the best EOIT is 130°CA BTDC,so that the heat release rate amplitude in the knock characteristic frequency band is controlled to a certain extent,resulting in the lowest KF,which proves this the compound injection scheme can suppress the knocking tendency of heavy load conditions to a certain extent.