Effect of Design and Operational Parameters of Piston Skirt on the Performance and Efficiency of a Small Gasoline Engine 2014-01-2016
Piston is a very important part of the engine as the contribution to its efficiency and performance is huge. This study is to understand in detail, the effect of piston skirt design on the functioning of an engine. A small gasoline engine was taken up for study. A commercially available numerical code PISDYN was used to analyze the piston liner interface. The Finite Element (FE) models of piston and the liner were used to simulate Elasto-Hydrodynamic Lubrication (EHL) between skirt / liner and piston pin / pin hole. Friction of the numerical model was validated through a tear-down motoring of the engine.
The secondary motion of the piston is studied. Understanding of how the profile and the ovality of the piston skirt affects the friction, wear and impact force at the piston liner interface is gathered. Asymmetrical skirt profile is proposed and its utility to reduce the thrust force on the liner and hence its friction and vibration of the engine is explained. The importance of piston-liner cold clearance, viscosity and liner surface roughness on skirt lubrication, friction and wear is understood. Also how piston pin offset and piston mass affects the thrust forces is seen. Based on the above understandings, conditions which would aid engine seizure and how it can be avoided are explained.