Optimization of Piston Skirt Profile Design to Eliminate Scuffing and Seizure in a Water Cooled Gasoline Engine 2015-01-1726

Piston is a critical component of the engine as it exposed to high inertial and thermal loads. With the advent of high performance engines, the requirement of the piston to perform in extreme conditions have become quintessential. Piston scuffing is a common engine problem where there is a significant material loss at the piston and the liner, which could drastically affect the performance and the longevity of the components. This detrimental phenomenon would occur if the piston is not properly designed taking into consideration the thermal and structural intricacies of the engine.

A water-cooled gasoline engine which had significant wear pattern on its piston skirt and liner was considered for this study. The engine block was made of aluminum alloy with a cast iron sleeve acting as liner. The piston-liner system was simulated through a commercially available numerical code which could capture the piston's primary and secondary motion. The lubrication mesh of the piston skirt and the cylinder liner was generated and overlaid on their corresponding FE meshes. The FE model was included to capture the Elasto-Hydrodynamic Lubrication (EHL) experienced between the skirts with the liner. The temperatures of the piston and the liner were derived from 3D Conjugate Heat transfer (CHT) analysis of the engine and these temperatures were used to derive the thermal deviation of the liner and the piston skirt. The bore deformation due to the bolting torque was analyzed separately through a 3D FEA non-linear solver and the liner deviation profile obtained was imported into the numerical model.

The two base piston profile designs (Design A and Design B) which had undesirable wear patterns were studied. How their skirt's linear and polar profile were contributing to scuffing was understood, based on which a new set of linear and polar skirt profile was developed to eliminate the scuffing issue. The aim of this study was not only to develop a numerical methodology which could predict the piston scuffing/seizure with good accuracy but also to garner a deep understanding of the cause and subsequently how to eliminate it. This paper would help engine designers understand which factors should be considered while making/modifying the skirt's linear and polar profile to reduce/eliminate piston scuffing/seizure.