Numerical Simulation Of CNG Engine Cycle

Simulation and experiment are two supports of internal-combustion engine research and development. The performance and emission characteristic of internal-combustion engine is decided by the reciprocity of the intake flow, in-cylinder mix and combustion process. Because temperature and composition is changed by space and time, limited information can be supplied by traditional engine test.In this paper, one-dimensional and three-dimensional simulation are performed with AVL BOOST and AVL FIRE about CNG engine working process. Flow and combustion are described detailedly and some parameters that affect the engine performance and emission characteristic are analyzed. The main research work include:(l)The whole CNG engine model is built up with BOOST, and the thermodynamics process is described macroscopically. The correctness of the engine model is proved by speed characteristics test at full load. On the base of the working model, performance simulation is carried out with changed compression ratio, ignition advance angle and valve timing. The influence of these parameters on CNG engine performance is studied by analyzing the simulation result. Some suggestions for engine development are put forward.(2) The three-dimensional moving meshes including intake port, cylinder and exhaust port are generated with FIRE, and reasonable boundary conditions and calculation model are selected. Good convergence result is achieved. Based on the computed result, the detail of fluid in intake port and cylinder, temperature distribution and the features of the combustion product are analyzed. Some suggestions for detail are put forward. The degree of thermal load and the incline of deflagrate at some operation conditions is appraised, which is for directing engine test.According to the one-dimensional simulation result, appropriate compression ratio, ignition advance angle and valve timing can increase engine power and decreasegas consuming. According to the three-dimensional simulation result, some unreasonable structure is found in intake port of the CNG engine. The local temperature in-cylinder of the CNG engine is much higher than diesel engine with sameness type, and the NOx emissions of the CNG engine keep a similar level with that of the sameness type diesel engine. Any development should be dealt with.