Abstract: Aiming at the special type and parameters optimization problem of distribution device in two-stroke mode of variable-cycle engine(VCE), the simulation models for four-stroke mode and two-stroke mode of VCE are established based on one single-cylinder four-stroke engine, the accuracy of simulation models is verified with cylinder pressure experiments, the composite performance coefficient for quantizing comprehensive performance evaluation is proposed based on multiple engine performance indexes, and its validity is verified with examples calculation and the method of fuzzy matter element. According to the maximum principle of composite performance coefficient, a series of simulation analysis on three schemes of cylinder exhaust port of two-stroke mode are carried out, draw a conclusion that, while the bottom edge of four rounded rectangle exhaust port coincidence with the bottom dead center，the best comprehensive performance of two-stroke mode in all engine speed is getting when Intake valves open at the 46 degrees crank angle before bottom dead center(BBDC) and close at the 86 after bottom dead center(ABDC), cylinder exhaust port width is 30 mm and height is 14 mm. The results indicate that, the engine performance in all speed can be quantizing comprehensive evaluation and comparison in high efficiency by the composite performance coefficient.

Key words: Comprehensive evaluation, Parameter optimization, Performance coefficient, Variable-cycle engine