Simulation Analysis Of Combined Supercharged Program And Supercharged Performance For Two-stroke Cycle Engine

Two-stroke engine is widely used as the small aviation power plant in China and abroad, but it’s most intuitionistic problem is that with the increase of altitude engine power decline is so large that usable elevation range is limited. However, supercharging technology as a very important and effective means to strengthen and recover the engine power, in the aspect of power recovery of two-stroke engine at middle and lower altitude was considered first. To improve pressure ratio and broaden the altitude scope of power recovery as much as possible, two-stage supercharging is adopted. But to avoid higher engine response, limited pressure ratio owing to exhaust energy shortage, and bad scavenging performance because of exhaust pressure increase using the two-stage turbocharger, the purpose of this thesis is to adopt combined supercharging (mech+turbo) to research power recovery of two-stroke engine at different altitudes.The two-stroke engine simulation model is established and verified according to the related parameters of the prototype. On this basis, the working performence of turbocharged two-stroke engine and supercharging system was studied under the reasonable supercharging matching at different altitudes. The results show that engine power of downstream throttle program containing a throttle controlling only engine load and a turbocharger adjusted by waste gate, achieves full recovery in 10 km where recyclable waste energy is still remaining, but declines due to lower pressure ratio over 10000m. Compared to non-supercharged engine, fuel consumption declines overall and its value largely depends on the scavenging loss, so that not only intake pressure but also exhaust pressure is controlled for supercharging of two-stroke engine.Based on mechanical supercharging simulation model, supercharged program using multi gear ratio and using intake throttle for two-stroke engine are researched respectively, and the working performence of supercharged engine and supercharging system is discussed. The results show that under the premise of reasonable matching, when power is full recovery, elevation range of program using multi gear ratio is wider than one using intake throttle, up to 6000 m, and fuel consumption of former is slightly lower within the critical altitude. The program using multi gear ratio is relatively complex in structure, but the program using intake throttle can achieve a smooth power output only by controlling throttle opening degree. In addition, the thesis presents and verifies the feasibility of the exhaust throttling pressure increase to control scavenging loss at high altitudes, so that the throttling action is used in model calculations.Finally, based on the related conclusions required from turbocharged and mechanical supercharged simulation research, analysis of supercharging program of the two-stroke engine and program’s characteristic reaches a conclusion that the program that mechanical supercharger works at low altitudes and two superchargers in series form work at high altitudes is relatively optimal, so that this progrom is studied by simulation experiments. The research results show:the turbocharger does not work within 4000m and begins to join with mechanical supercharger from 4000m; the method that throttle opens appropriately and intake reflux device works is adopted for compressor control in the condition of idle; when power of combined supercharged engine is full recovery, altitude range is wider (11 km), and exceeds one of the turbocharging program whose fuel consumption lower than that of former; steady and transient switching studies of supercharging system shows that switching process is the feasible and smooth.The results of this thesis can provide certain theoretical support and analysis basis.for supercharging development of light-weight port-injection two-stroke engine.