Non-Newtonian Elastohydrodynamic Lubrication Fluid Flow Modeling of Piston Skirts Considering Low Speed Effects in Initial Engine Start Up

2010 ◽  
Author(s):  
Syed Adnan Qasim ◽  
M. Afzaal Malik ◽  
Usman F. Chaudhri ◽  
Riaz A. Mufti
Keyword(s):  
Fluid Flow ◽  
Film Thickness ◽  
Relaxation Times ◽  
Viscoelastic Model ◽  
Elastohydrodynamic Lubrication ◽  
Computational Method ◽  
Solution Technique ◽  
Start Up ◽  
Piston Skirts ◽  
Engine Start

Elastohydrodynamic lubrication (EHL) is critically essential to minimize engine wear at low engine start up speeds. During the normal engine operations at medium to high speeds, non-Newtonian characteristics of multigrade engine lubricants enhance engine life by preventing adhesive wear. By incorporating viscoelastic effects of a non-Newtonian lubricant and focusing on different low engine start up speeds, this study models EHL fluid flow in the initial engine start up conditions. A 2-D non-Newtonian piston skirts lubrication model and analysis at the time of engine start up is presented based on the upper convected Maxwell viscoelastic model. The analysis of a non-Newtonian lubricant between piston and cylinder liner by using characteristic lubricant relaxation times in all order of magnitude analysis is done by using a perturbation method. The EHL film profile is predicted by solving the two-dimensional Reynolds equation using the inverse solution technique and the finite difference computational method in the fully flooded lubrication conditions. At different low engine start up speeds, the effect of viscoelasticity on lubricant velocity and pressure fields is examined and the influence of film thickness on lubricant characteristics is investigated. Numerical simulations show that piston eccentricities, EHD pressures and film thickness profiles are functions of low range of engine start up speeds. This study suggests that the initial engine start up speed at low range can be optimized as viscoelasticity produces a beneficial effect on piston skirt lubrication in the initial engine start up.

Modeling Viscous Isothermal Piston Skirts EHL in Very Low Initial Engine Start Up Speeds

2011 ◽  
Author(s):  
Syed Adnan Qasim ◽  
M. Afzaal Malik
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
High Viscosity ◽  
Solution Technique ◽  
Engine Operation ◽  
Low Speed ◽  
Start Up ◽  
Speed Optimization ◽  
Piston Skirts ◽  
Engine Start

In the normal low-speed engine operation, elastohydrodynamic lubrication (EHL) of piston skirts and lubricant rheology reduce friction and prevent wear. In a few initial start up cycles, a very low engine speed and absence of EHL cause adhesive wear. This study models hydrodynamic and EHL of piston skirts in the initial very low cold engine start up speed by using a high viscosity lubricant. The 2-D Reynolds equation is solved and inverse solution technique is used to calculate the pressures and film thickness profiles in the hydrodynamic and EHL regimes, respectively. The work is extended to investigate the effects of three very low initial engine start up speeds on the transverse eccentricities of piston skirts, film thickness profiles and pressure fields in the hydrodynamic and EHL regimes. Despite using a viscous lubricant, thin EHL film profiles are generated at low start up speeds. This study suggests very low speed optimization in the cold initial engine start up conditions to prevent piston wear under isothermal conditions.

Modeling Non-Newtonian Piston Skirts EHL in the Initial Engine Start Up

2010 ◽  
Author(s):  
Syed Adnan Qasim ◽  
Usman F. Chaudhri ◽  
M. Afzaal Malik ◽  
Riaz A. Mufti
Keyword(s):  
High Speed ◽  
Relaxation Times ◽  
Radial Clearance ◽  
Solution Technique ◽  
Engine Operation ◽  
Low Speed ◽  
Start Up ◽  
Piston Skirts ◽  
Engine Start ◽  
Speed Engine

In the normal high speed engine operation at small piston-to-bore radial clearance, elastohydrodynamic lubrication (EHL) of skirts and non-Newtonian lubricant behavior prevent adhesive wear, but in the initial engine start up, the large clearance, low speed and absence of EHL, cause start up wear. This study models 2-D upper convected Maxwell viscoelastic EHL of piston skirts at small radial clearance in a few initial low speed engine start up cycles by solving the Reynolds equation and using the inverse solution technique. The numerical analysis incorporate characteristic lubricant relaxation times and a perturbation method to predict and compare hydrodynamic and EHL pressures and film profiles. The effects of viscoelasticity on the lubricant characteristics, transverse eccentricities of piston, film thickness, and pressure fields in the hydrodynamic and EHL regimes are investigated. This study suggests that EHL film is formed at very small piston-to-bore radial clearance at low start up speed under assumed conditions to prevent start up wear as viscoelasticity produces a beneficial effect on piston skirts lubrication in the initial engine start up.

Effects of High Initial Engine Start Up Speeds in Isothermal Fluid Flow and Piston Skirts EHL

2011 ◽  
Author(s):  
Syed Adnan Qasim ◽  
M. Afzaal Malik
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Adhesive Wear ◽  
Cooling System ◽  
Cylinder Liner ◽  
Operating Conditions ◽  
Solution Technique ◽  
Start Up ◽  
Piston Skirts ◽  
Engine Start

In the medium and high speed normal engine operating conditions a fully established elastohydrodynamic lubricating (EHL) film between the piston skirts and cylinder liner surfaces reduces friction and prevents adhesive wear. In the initial engine start up the absence of EHL film causes wear of piston skirts, especially at high speeds. In a few initial cold engine start up cycles, a highly efficient cooling system may not let the temperature to rise significantly and affect the viscosity and other characteristics of a lubricant. In view of the vulnerability of piston skirts to adhesive wear at high initial engine start up speeds, the hydrodynamic and EHL of piston skirts is modeled numerically. A 2-D Reynolds equation is solved by coupling the secondary piston motion and using a finite difference scheme. Transient hydrodynamic film thickness profiles are generated at a relatively high engine start up speed. In the EHL regime, the profiles of rising hydrodynamic pressures and film thicknesses are predicted by using the inverse solution technique in fully flooded conditions. The study is extended to a range of high engine start up speeds while using a fairly viscous engine lubricant. Numerical simulations show significant changes in the piston eccentricities and film thickness profiles in the hydrodynamic and EHL regimes at different start up speeds. Such variations alter the hydrodynamic and EHL pressures and visibly affect the load carrying capacity of the lubricant. This study suggests to optimize the high engine start up speed for the given viscosity grade engine lubricant when considering the vulnerability of skirts and liner surfaces to adhesive wear in the initial engine start up.

Modeling Shear Heating in Piston Skirts EHL Considering Different Viscosity Oils in Initial Engine Start Up

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
S. Adnan Qasim ◽  
M. Afzaal Malik ◽  
M. Ali Khan ◽  
R. A. Mufti
Keyword(s):  
Thermal Loading ◽  
Energy Equation ◽  
Adhesive Wear ◽  
Solution Technique ◽  
Engine Operation ◽  
Start Up ◽  
Shear Heating ◽  
Viscosity Grade ◽  
Piston Skirts ◽  
Engine Start

A fully established elastohydrodynamic lubricating (EHL) film between the piston and the liner surfaces during normal engine operation minimizes piston slap and prevents adhesive wear. Wear cannot be prevented in the initial engine start up due to the absence of EHL film. During normal engine operation, thermal loading due to combustion dominates piston skirts lubrication. However, in a few initial cold engine start-up cycles, shear heating affects the lubricant viscosity and other characteristics considerably. This study models 2D piston skirts EHL by incorporating shear heating effects due to lubricant flow between the skirts and liner surfaces. The hydrodynamic and EHL film profiles are predicted by solving the 2D Reynolds equation and using the inverse solution technique, respectively. The temperature distribution within the oil film is given by using the 2D transient thermal energy equation with heat generated by viscous heating. The numerical analysis is based on an energy equation having adiabatic conduction and convective heat transfer with no source term effects. The study is extended to low and high viscosity grade engine oils to investigate the adverse effects of the rising temperatures on the load carrying capacity of such lubricants. Numerical simulations show that piston eccentricities, film thickness profiles, hydrodynamic and EHL pressures visibly change when using different viscosity grade engine lubricants. This study optimizes the viscosity-grade of an engine lubricant to minimize the adhesive wear of the piston skirts and cylinder liner at the time of initial engine start up.

Two-Dimensional Elastohydrodynamic Lubrication Fluid Flow Modeling of Piston Top Ring Considering Elastic Deformation in Initial Engine Start Up

2010 ◽  
Author(s):  
M. Afzaal Malik ◽  
Syed Adnan Qasim ◽  
Ali Usman ◽  
Riaz A. Mufti
Keyword(s):  
Elastic Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Solution Technique ◽  
Two Dimensional ◽  
Lubricating Film ◽  
Start Up ◽  
Lubrication Condition ◽  
Piston Ring Lubrication ◽  
Cylinder Bore ◽  
Engine Start

The absence of Elastohydrodynamic Lubrication (EHL) between the first piston compression ring (top ring) and the liner surface in the initial engine startup causes adhesive wear whereas the presence of such a film enhances engine life by wear prevention. In the current work, a two dimensional model is presented for barrel-faced ring profile by considering elastic deformation and EHL. A non-axisymmetric elliptical cylinder bore and an elastic ring are considered to determine circumferential flow. The EHL film profile is generated by solving the two dimensional Reynolds equation using inverse solution technique and finite difference method in fully flooded lubrication condition. The results show that piston ring lubrication depends on the bore shape or bore out-of-roundness and lubricating film thickness due to which circumferential flow gets significantly reduced during the initial engine start up.

Shear Heating of High-Viscosity Grade Lubricant in Piston Skirts: EHL at Idling Speeds in Initial Engine Start Up

2012 ◽  
Author(s):  
Syed Adnan Qasim ◽  
Mumtaz Ali Khan ◽  
M. Afzaal Malik
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Film Thickness ◽  
Source Term ◽  
High Viscosity ◽  
Start Up ◽  
Shear Heating ◽  
Viscosity Grade ◽  
Piston Skirts ◽  
Engine Start

A few initial cold engine start up cycles at low idling speeds do not prevent wear due to the absence of a fully established elastohydrodynamic lubrication (EHL) film between the piston skirts and the cylinder liner. It happens when the thermal loading due to combustion may be ineffective initially, and shear heating becomes significant as a result of the sliding motion of the piston. This study models the 2-D piston skirts EHL at the idling speeds in the initial engine start up by using a high-viscosity grade engine oil and incorporating the shear heating effects. The 2-D heat transfer equation is used with no source term effects to study the temperature changes and their effects on the viscosity of a Newtonian lubricant at the different idling speeds in the initial start up of an internal combustion engine. The 2-D Reynolds equation is solved numerically to generate the hydrodynamic pressures as the function of 720 degrees crank rotation cycle. Under the flooded lubrication conditions the inverse solution technique is employed to generate the hydrodynamic pressures in the EHL regime. The numerical analysis at the two different idling initial engine start up speeds is presented based on the 2-D heat equation having adiabatic conduction and convective heat transfer with no source term effects. Viscous dissipation coupled with the piston motion, the pressure fields generation, the temperature effects on the viscosity of the lubricant and the subsequent oil film thickness profiles in the contact region are examined. The influence of the low-temperature shear heating on the hydrodynamic and EHL film thickness at the time of initial engine start up are investigated. This study suggests that by using a high-viscosity grade oil in the idling speed engine start up the film temperature rises non-uniformly due to shear heating in the hydrodynamic and EHL regimes. The low temperature rise affects the pressure and temperature dependent oil viscosity, and the secondary transverse eccentric displacements of the piston. Resultantly, the piston skirts lubrication is affected despite the initial engine start up at the idling speeds.

Modeling EHL of Rough Piston Skirts Using Different Viscosity-Grade Lubricants in Initial Engine Startup

2012 ◽  
Author(s):  
Syed Adnan Qasim ◽  
Mubashir Gulzar ◽  
Riaz A. Mufti ◽  
M. Afzaal Malik
Keyword(s):  
Cylinder Liner ◽  
High Viscosity ◽  
Solution Technique ◽  
Engine Operation ◽  
Start Up ◽  
Viscosity Grade ◽  
Piston Skirts ◽  
Interacting Surfaces ◽  
Engine Start ◽  
Lubrication Models

An engine lubricant plays a significant role in preventing adhesive wear of the rough interacting surfaces of the piston skirts and the cylinder liner. A fully established elastohydrodynamic lubricating (EHL) film, appropriate viscosity oil and the fairly rough interacting surfaces prevent wear during normal engine operation. The absence of an EHL film and inappropriate viscosity lubricant fail to minimize wear in the initial engine startup. This work considers a fairly viscous Newtonian engine lubricant to model the rough piston skirts hydrodynamic and EHL in the initial engine start up. The isotropic surfaces of the skirts and the cylinder liner having different roughness amplitudes are considered in the basic lubrication models. The flow factors are introduced in the 2-D average Reynolds equation, which is solved numerically to generate the hydrodynamic pressures. The inverse solution technique is used to develop the basic EHL model of the rough surfaces. The secondary piston dynamics and the contact geometry of interacting surfaces are incorporated in the basic lubrication models. The profiles of the piston eccentricities, secondary velocities, film thicknesses and pressures are generated as the function of 720 degrees crank rotation cycle. The study is extended to develop the lubrication models for the low and high viscosity grade engine lubricants separately. The simulation results are analyzed and compared with those of the basic lubrication model. The results show that the different lubricant viscosities alter the secondary displacements of the sliding piston and affect the lubrication of the rough interacting surfaces. The comparative analysis leads to optimize the use of appropriate viscosity-grade engine lubricant for a few low speed initial engine startup cycles.

Modeling of Shear Heating in Elastohydrodynamic Lubrication of Piston Skirts by Considering Different Viscosity Oils in Initial Engine Start Up

2010 ◽  
Author(s):  
M. Afzaal Malik ◽  
Syed Adnan Qasim ◽  
Mumtaz Ali Khan ◽  
Riaz A. Mufti
Keyword(s):  
Thermal Loading ◽  
Energy Equation ◽  
Adhesive Wear ◽  
Cylinder Liner ◽  
Solution Technique ◽  
Engine Operation ◽  
Start Up ◽  
Shear Heating ◽  
Piston Skirts ◽  
Engine Start

The presence of fully established elastohydrodynamic lubricating (EHL) film between piston skirt and cylinder liner during normal engine operation prevents adhesive wear, piston noise and slap. The absence of EHL in the initial engine start up fails to prevent the same. During normal engine operation, thermal loading due to combustion dominates piston skirts lubrication. However, in a few initial cold engine start up cycles, shear heating may be assumed to considerably affect the lubricant viscosity and other characteristics. This study undertakes a 2-D EHL modeling of piston lubrication by incorporating shear heating effects due to lubricant flow between skirts and liner surfaces. The EHL film profile is predicted by solving the 2-D Reynolds equation using inverse solution technique and the finite difference method in fully flooded lubrication conditions. The temperature distribution within oil film is given by using the 2-D transient thermal energy equation with heat generated by viscous heating. The numerical analysis is based on energy equation having adiabatic conduction and convective heat transfer with no source term effects. The study is extended to a number of engine lubricants having different viscosities to investigate the extent of adverse effects due to temperature rise on load carrying capacity of lubricants. Numerical simulations show that piston eccentricities, film thickness profiles, hydrodynamic and EHL pressures visibly change when using different viscosity grade engine lubricants. This study suggests that a lubricant of appropriate viscosity can be optimized keeping in view the vulnerability of piston skirts and cylinder liner to adhesive wear at the time of initial engine start up.

Effects of Multi-Grade Oils in Modeling Non-Newtonian Rheology Between Piston and Cylinder Surfaces in Engine Initial Start Up Conditions

2014 ◽  
Author(s):  
Usman Chaudhri ◽  
Kendrick Aung
Keyword(s):  
Film Thickness ◽  
Hydrodynamic Lubrication ◽  
Fluid Velocity ◽  
Computational Method ◽  
Type Model ◽  
Perturbation Scheme ◽  
Reynolds Equations ◽  
Linear Partial Differential Equations ◽  
Start Up ◽  
Secondary Motion

This paper presents the results of a transient analysis of hydrodynamic lubrication between piston and cylinder surfaces in engine Initial startup conditions with a Non Newtonian lubricant under oscillatory motion. Effects of different multi-grade oil viscosities are also investigated in the simulation. The time dependent Reynolds equations use a Maxwell type model to analyze fluid rheology. A perturbation scheme is used to derive coupled non linear partial differential equations to obtain the fluid velocity. The oil film profile is predicted by solving the two-dimensional Reynolds equations using the finite difference computational method. The piston velocities in engine secondary motion are adjusted by using fourth order Runge-Kutta technique. Using different oil viscosities, the effect of viscoelasticity on lubricant velocity and pressure fields is examined and the influence of film thickness on lubricant characteristics is investigated. Numerical simulations show that piston eccentricities and film thickness profiles vary under different multi grade oils at engine start up conditions.

Analysis of EHL Circular Contact Start Up: Part I—Mixed Contact Model With Pressure and Film Thickness Results

2000 ◽  
Vol 123 (1) ◽  
pp. 67-74 ◽  
Author(s):  
Jiaxin Zhao ◽  
Farshid Sadeghi ◽  
Michael H. Hoeprich
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Iteration Scheme ◽  
Mixed Lubrication ◽  
Contact Forces ◽  
Solid Contact ◽  
Start Up ◽  
Lubricated Contact

In this paper a model is presented to investigate the start up condition in elastohydrodynamic lubrication. During start up the lubrication condition falls into the mixed lubrication regime. The transition from solid contact to lubricated contact is of importance when investigating the start up process and its effects on bearing performance. The model presented uses the multigrid multilevel method to solve the lubricated region of the contact and a minimization of complementary energy approach to solve the solid contact region. The FFT method is incorporated to speed up the film thickness calculation. An iteration scheme between the lubrication and the solid contact problems is used to achieve the solution of the mixed lubrication contact problem. The results of start up with smooth surfaces are provided for the case when speed increases from zero to desired speed in one step and the case when speed is linearly increased to desired speed. The details of the transition from full solid contact to full lubricated contact in EHL start up are presented. The change of pressure and film thickness as well as contact forces and contact areas are discussed.

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