COMPRESSION RING HYDRODYNAMIC AND ELASTOHYDRODYNAMIC LUBRICATION MODELING IN THE INITIAL ENGINE START UP.PDF

Abstract

Modern engine design demands better fuel economy, reduced exhaust emissions, increased recyclability, freedom from hazardous substances and enhanced operating life. To fulfill these requirements, automobile engine manufacturers ensured that piston ring design must reduce frictional power loss, oil transport into the combustion chamber, and wear, as piston ring account for majority of the mechanical power loss of the internal combustion engine. Aforementioned requirements and function can be fulfilled only and only if piston ring is fully flooded with controlled amount of lubricant oil at inlet region, to generate Elastohydrodynamic lubricating film between piston ring and cylinder liner to separate these sliding surfaces from each other, hence preventing adhesive wear and dry contact. Oil starvation and absence of fully developed lubricating film results in dry contact followed by sequential formation of boundary, mixed, hydrodynamic and then elastohydrodynamic lubricating film in initial engine start up. This sequence of film development in engine startup period results in drastic increase in friction, power loss, wear and ultimately compromised engine operating life. Advancement in numerical and experimental investigation of static and dynamic analysis of piston ring performance showed that cylinder liner is not perfectly circular due to high combustion pressure forces, thermal distortion, variable load at major and minor thrust sides, wear, head clamping forces and manufacturing errors. This liner distortion results in reduction in magnitude of the minimum lubricating film thickness due to circumferential flow of lubricant oil, but decreased overall power loss and increased exhaust emissions due to oil transport in to the combustion chamber. In this research work Two-Dimensional hydrodynamic and elastohydrodynamic model is developed and is simulated in initial engine startup conditions. Parametric study is conducted for piston ring running face profile, engine speed and degree of distortion in non-circular cylinder liner. Results show that parabolic ring running face profile is best suited for improved lubricating film thickness profile and performance. Results also show that with increase in speed, film thickness profile improves but ring performance decreases, and with increase in magnitude of bore distortion, film thickness profile and ring performance improve, except oil transport to combustion chamber, which also increases.