Study On Performance Simulation Of Variable Combustion Chamber Engine

The technical feasibility of VCC (Variable Combustion Chamber) piston is validated by means of engine performance simulation. The piston movement is modified during the performance simulation of VCC engine, and the iteration method of coupling the performance simulation with the dynamics simulation is presented. The simulating model of VCC engine is built up by using AVL-Boost software, and coupling simulation is conducted to forecast the fuel economy and power output of VCC engine. The influence of VCC technology on cycle-to-cycle combustion fluctuation is analyzed.The variations of combustion chamber volume are caused by VCC displacement (The displacement of VCC piston crown relative to VCC piston skirt) during combustion. VCC piston movement includes not only the piston displacement by a connection rod-crank mechanism, but also VCC displacement. While VCC piston movement is determined, VCC engine performance simulation can be conducted by using some of commercial engine performance simulation software such as AVL-Boost.VCC displacement and in-cylinder pressure during combustion process are interdependent and influenced with each other, which displays intense nonlinear characteristic. The iteration method of coupling the performance simulation with the dynamics simulation is presented for the problem, and the iterative convergence criteria and iterative formula are also presented.VCC gasoline engine performance simulation mode is built with AVL-Boost, by which the technical feasibility of VCC piston technology is validated from coupling and iteration simulation. The results from the coupled simulation indicate that1) VCC piston technology can meet the fast response demands of vehicle engines at various different working conditions including transient loads and speeds, and2) excess in-cylinder pressure of high compression ratio engine can be limited at heavy loads by means of VCC piston, and3) the fuel economy is increased up at all loads, about10%improvement at heavy loads and20%improvement at light loads. The influence of cycle-to-cycle combustion fluctuation by VCC piston technology is forecasted by using coupling simulation. The simulation method of cycle-to-cycle combustion fluctuation is presented, the simulation model of cycle-to-cycle combustion fluctuation is also built, the result shows that cycle-to-cycle combustion fluctuation can be effectively improved by VCC piston technology, the fluctuation range of in-cylinder pressure will be reduced by51%.