Abstract: Combustion gas pressures were tested experimentally both before and after supercharge. The designed dimensions of piston were introduced both before and after cylinder diameter enlargement. To find out piston’s movement trajectory and transversal velocity, an analysis model was established based on hydrodynamic lubrication theory and piston dynamics. Newton-Raphson method was chosen to solve the dynamical equation. Finite difference method and successive over-relaxation method were used to solve average Reynolds equation. The results show that the swing range of the piston movement trajectory is enlarged after supercharge and cylinder diameter enlargement, and the transversal velocity is raised. Those factors lead to the increase of the possibility of scuffing cylinder liner and bringing about stronger shock to cylinder. The lubricant viscosity between surface of piston and cylinder liner must be denser to adapt to work condition after the supercharge design. The anti-scuffing function should be enhanced simultaneously in the design of supercharge and cylinder diameter enlargement.

Key words: mechanics , diesel engine , supercharge , cylinder diameter enlargement , trajectory