A Numerical Model to Study the Role of Surface Textures at Top Dead Center Reversal in the Piston Ring to Cylinder Liner Contact

Abstract

Minimisation of parasitic losses in the internal combustion engine is essential for improved fuel efficiency and reduced emissions. Surface texturing has emerged as a method palliating these losses in instances where thin lubricant films lead to mixed or boundary regimes of lubrication. Such thin films are prevalent in contact of compression ring to cylinder liner at piston motion reversals because of momentary cessation of entraining motion. The paper provides combined solution of Reynolds equation, boundary interactions and a gas flow model to predict the tribological conditions, particularly at piston reversals. This model is then validated against measurements using a floating liner for determination of in-situ friction of an engine under motored condition. Very good agreement is obtained. The validated model is then used to ascertain the effect of surface texturing of the liner surface during reversals. Therefore, the paper is a combined study of numerical predictions and the effect of surface texturing. The predictions show that some marginal gains in engine performance can be expected with laser textured chevron features of shallow depth under certain operating conditions. Keywords: A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d

A hydrodynamic flow analysis for optimal positioning of surface textures

“…The ring profile in this case is parabolic with a ring contact face-width of 0.8 mm. Etsion and Sher [3] reported similar findings for a thicker ring of broader face-width. Nevertheless, the results of both studies show remarkable agreement.…”

“…Etsion and Sher [3] reported a significant reduction of up to 4% in fuel consumption with measurement repeatability of ±0.5% using a partially etched piston compression ring. This was very similar to that reported in [2,6], where the surface of cylinder liner in a high performance engine was etched at the piston top dead centre (TDC) reversal.…”

“…The carried load must equate the applied conjunctional load as the result of ring tension and combustion gas pressure acting behind the inner rim of the ring, both of which strive to adhere the ring to the cylinder liner surface, F [3,11,23]. Therefore, the following convergence criterion should be met:…”

“…More comprehensive solutions, including 2-dimesional analysis with thermal effects, sideleakage flow and surface roughness are provided elsewhere [3,11,28,29].…”

“…These include texturing of cylinder liner surfaces in the vicinity of top piston ring reversal at the top dead centre (TDC) [2,3] or partial surface texturing of the piston ring itself [4]. Texturing has been shown to improve/palliate mixed and boundary regimes of lubrication which are predominant at piston reversals, sometimes reducing incylinder friction by as much as 2-4% [5][6][7].…”