Experimental Study On Performance Of 15kW Two-stroke Ignited PFI Kerosene Piston Engine

Due to the requirements of fuel transportation and use.The two-stroke aero-piston engine,which is widely used in light unmanned aerial vehicle,has been paid more and more attention to the development of ignition heavy fuel engine technology currently.The heavy fuel used in aero-piston engine includes aviation kerosene and diesel fuel which has the property of high flash point and poor evaporation.It is hard to form combustible mixture in the cylinder.The two-stroke aero-piston engine is hard to cold-start,burn unstable in low speed and small load condition.It is prone to knock when burning because of the low octane number of the fuel,So many internal combustion engine workers have been working on the combustion technology of two-stroke ignited heavy engine in recent years.This paper focuses on the numerical prediction and experimental study of the knock characteristics of two-stroke kerosene engine.The influence of ignition timing and air-fuel ratio on engine combustion under different operating conditions is analyzed by numerical simulation,and the numerical optimization is made to make the engine achieve higher performance requirements;The cold-start test of kerosene engine and the calibration test of fuel injection and ignition timing electronic control system under partial load condition are completed,the influence of knock on the performance of kerosene engine under different working conditions are studied.Its specific work is as follows:(1)A prototype engine 1D performance simulation model is established by using GT-power,and the contrast error between the simulation results and the test data measured by the prototype gasoline engine dynamometer platform is guaranteed to be within 5%.Taking kerosene as fuel,the predictive combustion model which can predict knock is used,and the influence of different ignition timing and air-fuel ratio on the knock characteristics is studied,the optimization of ignition timing and air-fuel ratio are realized by DOE method.The study shows that delayed ignition timing is helpful to restrain knock,but too much delayed ignition timing has great influence on power.When the air-fuel ratio is about 11 kerosene engine is prone to knock in heavy load,and the mixture with too thick or too dilute has the effect of suppressing the knock;The ignition timing and air-fuel ratio are selected by Latin hypercube,and the power recovery coefficient of the kerosene engine are reached about 80% by GA standard genetic algorithm.(2)The prototype propeller test bench is established,and the heavy propeller with large pitch is matched,the kerosene engine is started successfully by preheating the cylinder head and enriching mixed gas.At the same time,the calibration test of fuel injection pulse width and ignition timing of electronic control system is completed.The results show that when the spark plug gasket on the cylinder head is heated 60 ? and increased the injection pulse width,the kerosene engine start quickly.In low speed and small load,two-stroke kerosene engine is very unstable which has serious fire extinguishing and the different combustion state of the two cylinder,the exhaust temperature difference reaches 140?,because of the cold cylinder head.When the throttle opening is 63°and the speed is 5600 rpm the knock is effectively suppressed by postpone 1.2°CA ignition timing;Compared with gasoline,the cylinder head temperature is lower,the performance output of two fuel engines with a throttle opening of less than 40° is quite.When the throttle opening exceeds 50°,the kerosene engine speed is less than 200 rpm of gasoline engine;When using small pitch propeller,kerosene engine speed can reach more than 7200 rpm,it meet design requirements.(3)The test calibration of kerosene engine under medium and small load was completed on the dynamometer bench.The results show that the pressure in the cylinder during the engine knock has a high frequency fluctuation,the maximum pressure is more than 3 times of the normal combustion,and the strong knock will cause the power to drop sharply.Delay ignition timing can inhibit the knock,but cause the rise of exhaust temperature,the exhaust temperature has obviously reduced by thickening the mixing gas,and the detonation is eliminated.The engine running well when excess air coefficient is maintained at 0.85~0.9;Finally,when the throttle opening is 55°,the recovery coefficient is between 82%~86% by compare the torque and power test data of kerosene engine with the torque and power test data of prototype.