CFD Simulation Study Of The Fuel-Air Mixture Formation In Cylinder Of The Two-Stroke Heavy Fuel Spark Ignition Engine

Because of the poor vaporization of the heavy fuel and the high tumble velocity in the cylinder near the end of the compression of the two-stroke engine, injection timing has a great influence on the concentration distribution of the fuel-air mixture in the cylinder, which affects the combustion stability of the engine. To ensure the safety of the engine during the calibration experiments, this paper simulates the process of the fuel-air mixture formation in the cylinder of the two-stroke heavy fuel ignition engine at different speeds and different loads by CFD. The results are as follows: When engine is at 4000 rpm and the throttle angle is 18°, the angle at the end of injection is 40°CA BTDC, the concentration of the fuel-air mixture around the spark plugs is thin, which explained the reasons for the misfire of the engine at the same condition during the former experiments. When the throttle angle is18°, the engine is at 4000 rpm and 4500 rpm, the suitable angles at the end of injection are around80°~120°CA BTDC and 100°~140°CA BTDC. When the engine is at 4000 rpm, the throttle angles are18°,32°and 44°, the suitable angles at the end of the injection are around 80°~120°CA BTDC,100°~160°CA BTDC and 120°~160°CA BTDC, which illustrates that the angle at the end of the injection has an tendency to be advanced with the increasing of the throttle angle. When the engine is4000 rpm, at the low loads(18°), the spark plug far from the exhaust passage plays the main role to ignite and the other is assisted; However, at the middle load(32°) and the big load(44°) conditions, the spark plug near the exhaust passage plays the main role to ignite, and the other is assisted, which has proved the necessary of two spark plugs for direct injection engines.At the end of this paper, experiments were done on the two-stroke heavy fuel ignition engine.The results are as follows: when the throttle angle is 18°, the best angles at the end of the injection at4000 rpm and 4500 rpm are 100° CA BTDC and 130°CA BTDC; When the engine is at 4000 rpm,the best angles at the end of the injection at 32° and 44° are 140° CA BTDC and 150°CA BTDC. The results verified the consistency of the computational results, so as to offer some instructions for the injection control strategy of the engine calibration experiments.