Abstract
The paper presents a mixed thermo-hydrodynamic analysis of elliptic bore bearings using combined solution of Navier–Stokes, continuity and energy equations for multi-phase flow conditions. A vapour transport equation is also included to ensure continuity of flow in the cavitation region for the multiple phases as well as Rayleigh–Plesset to take into account the growth and collapse of cavitation bubbles. This approach removes the need to impose artificial outlet boundary conditions in the form of various cavitation algorithms which are often employed to deal with lubricant film rupture and reformation. The predictions show closer conformance to experimental measurements than have hitherto been reported in the literature. The validated model is then used for the prediction of frictional power losses in big end bearings of modern engines under realistic urban driving conditions. In particular, the effect of cylinder deactivation (CDA) upon engine bearing efficiency is studied. It is shown that big-end bearings losses contribute to an increase in the brake specific fuel consumption with application of CDA contrary to the gains made in fuel pumping losses to the cylinders. The study concludes that implications arising from application of new technologies such as CDA should also include their effect on tribological performance.
Highlights
The main considerations in modern engine development are fuel efficiency and compliance with progressively stringent emission directives
It is shown that bigend bearings losses contribute to an increase in the brake specific fuel consumption with application of cylinder deactivation (CDA) contrary to the gains made in fuel pumping losses to the cylinders
One of the main conclusions of the current study is the importance of determining the correct boundary conditions in the study of journal bearing lubrication
Summary
Greek symbols a Thermal diffusivity a0 Pressure/temperature–viscosity coefficient b Lubricant bulk modulus b0 Viscosity–temperature coefficient DT Lubricant temperature rise e Eccentricity ratio / Connecting rod obliquity angle c Fraction lubricant film ratio d Journal’s attitude angle D Local deflection of the Babbitt overlay Dij Kronecker delta h Circumferential direction in bearing f Number of asperity peaks per unit contact area g Lubricant dynamic viscosity g0 Lubricant dynamic viscosity at atmospheric pressure j Average asperity tip radius k Stribeck’s oil film parameter l Pressure coefficient for boundary shear strength of asperities m Poisson’s ratio q Lubricant density q0 Lubricant density at atmospheric pressure s Shear stress s0 Eyring shear stress C Diffusion coefficient x Angular speed of the crankshaft (engine speed)
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