Research On Combustion And Performance Of Compression-ignition Aviation Piston Engine At Different Altitudes

Compression ignition aviation piston engine has the characteristics of low fuel consumption and high safety.It is a research hotspot and trend in the aviation piston engine industry.China's support for general aviation is increasing,aviation piston engine as the main power source of general aviation,domestic research on it is still in the initial stage,few research reports have been published,and a number of key technologies have not been solved,need to be further studied.Combustion characteristics and performance of compression ignition aviation piston engine at different altitudes are studied and analyzed,which can provide reference for independent research and development of aviation piston engine in China.In this paper,a compression ignition type aviation piston engine produced abroad is taken as the research object,and an aviation piston engine test bench with air inlet air conditioning is built.The air inlet air conditioning is used to simulate the atmospheric pressure at different altitudes.Combustion and emission characteristics tests of compression-fired aircraft piston engines at different altitudes were carried out.Through the tests,the variation laws of engine dynamic performance,economic performance,combustion and emission characteristics with altitude were obtained.The simulation model of compression-ignition aviation piston engine was built by AMESim software and verified by test data.The influence of fuel injection parameters on the combustion characteristics and performance of the aviation piston engine is studied by using the simulation model,and the influence of compression ratio on the combustion and performance of the aviation piston engine is further studied.Based on the analysis of simulation contents,a method to improve the performance of aviation piston engines in a high altitude environment is proposed.In the external characteristics tests of aviation piston engines at three different altitudes,according to the test data,the following conclusions are drawn: with the increase of altitude,under the same working condition,the excess air coefficient decreases,the intake mass flow rate decreases,the effective fuel consumption rate increases,and the power decreases to a certain extent.In the external characteristic test,the torque of the engine does not decrease with the increase of the engine speed,which is a typical characteristic curve of the propeller of the aviation piston engine.NOx emission,HC emission and CO emission all increased slightly with the increase of altitude.The soot emission also gradually increases with the increase of altitude,and the soot emission at low and high speed external characteristics is the highest among all the rotating speeds.In the load characteristic tests of aviation piston engines at three different altitudes,according to the test data,the following conclusions are drawn: with the increase of altitude,the intake mass flow rate and excess air coefficient decrease,the effective fuel consumption rate increases,and the effective thermal efficiency decreases.The higher the altitude,the lower the maximum combustion pressure,the longer the ignition retardation period,the later the combustion starting point,and the higher the maximum average combustion temperature.With the increase of altitude,the combustion duration of the maximum cruising speed is prolonged under low and medium load conditions,and it is shortened under high load conditions.With the increase of altitude,the NOx emission trend increases at each working point,and the CO emission increases more obviously at small and large loads,while there is no significant change near medium loads.HC emission increases with the increase of altitude,but decreases with the increase of load.The increase of HC emission under small load is greater than that under large and medium load.Soot emission increased significantly with the increase of altitude,and showed a trend of decreasing first and then increasing with the increase of load.In the simulation study of compression ignition type aviation piston engine,the following conclusions are drawn :(1)With the increase of nozzle number and decrease of aperture,the combustion starting point is advanced,the ignition delay period is shortened,the combustion duration is shortened,the combustion center of gravity is closer to TDC,the combustion is more sufficient,and the thermal efficiency of the cycle is improved.Under high altitude environment,the injector with multiple orifice and small aperture can effectively alleviate the problem of poor atomization quality of aviation kerosene itself,help to restore engine power,reduce fuel consumption rate,improve the dynamic performance and endurance performance of aviation aircraft,but will increase the production of NOx.In practical application,the number and aperture of jet holes should be adjusted reasonably.(2)In the high altitude environment,when the compression-fired aviation kerosene piston engine runs in the maximum cruising condition,the peak pressure of the cylinder increases with the increase of the injection advance Angle,and the time point of the peak point moves forward,and the pressure rise rate increases,resulting in the rough operation of the engine and other problems.The larger the injection advance Angle is,the higher the peak value of the instantaneous heat release rate is,the corresponding crankshaft rotation Angle is advanced,the combustion delay period is shortened,the combustion starting point and the combustion center of gravity are advanced,the combustion duration is shortened,and the effective thermal efficiency is higher.Advance injection can effectively improve the dynamic performance and fuel economy of the aviation piston engine,but it will increase NOx emission.(3)under high altitude environment,compression ignition aviation kerosene engine piston to maximum cruising operation,the highest pressure in cylinder with increased obviously with the increase of injection pressure,maximum combustion explosion pressure in the moment of basically remain unchanged,the higher the rate of pressure rise,at the same time help to improve the quality of aviation kerosene spray,high altitude environment to accelerate the process of combustion.The higher the injection pressure,the closer the combustion starting point and the combustion center of gravity are to the top dead center,the shorter the combustion duration,the higher the effective thermal efficiency,the higher the peak heat release rate,the higher the engine's power capacity and the fuel economy are improved,but the maximum temperature in the cylinder will rise,and the NOx generation will increase.(4)Under the maximum cruising condition and take-off condition,with the increase of compression ratio,the maximum burst pressure and the maximum pressure rise rate of the aviation piston engine will increase,but it will cause rough engine operation.With the increase of the compression ratio,the power and torque of the engine increase and the effective fuel consumption rate decrease under the two working conditions.At the same time,the exhaust temperature of the engine is reduced,indicating the thermal efficiency is improved,the economy is improved,and the thermal load of the compression ignition engine is improved.