M. Afzaal Malik

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

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.

A Comparative Study of Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundles Using Bond Graph Approach

Flow-induced vibration (FIV) has been a major concern in the nuclear and process industries involving steam generator and heat exchanger tube bundle design. Various techniques and models have been developed and used for the analysis of cross-flow induced vibration of tube bundles. Bond Graph approach has been applied to existing FIV excitation models, followed by a comparative study. Results have been obtained using 20-SIM software. It is expected that the current approach will give a new dimension to the FIV analysis of tube bundles.© 2005 ASME

Modeling and Simulation of Elastohydrodynamic Lubrication of Piston Skirts Considering Elastic Deformation in the Initial Engine Start-Up

The presence of Elasto-hydrodynamic Lubrication (EHL) film between opposing piston and liner surfaces prevents possible solid-to-solid contact and wear. This enhances engine life manifold as compared to when the EHL film is non-existent in the initial engine startup or breaks down during normal engine operation. Forced dry sliding of piston during engine cranking followed by partial lubrication in the initial engine startup leads to adhesive wear. This research investigates the possibility of an EHL film on such an occasion by considering elastic deformation of opposing piston skirt and liner surfaces due to Elasto-hydrodynamic (EHD) pressures. The geometry of piston skirts is defined and governing equations are applied to determine hydrodynamic pressures. The EHL film thickness profile generated by inverse solution technique and its expression is defined by incorporating contact geometry and EHD pressures in the piezoviscous regime. A computer code is developed and used to simulate the performance parameters and their behavior during initial engine startup. Due to critical factors such as engine speed, redial clearance between piston skirts and liner and lubricant viscosity, a time dependent 2-D EHL film profile is generated. The simulated results indicate that, despite piston eccentricities due to secondary oscillatory motion, EHL film established between the opposing piston skirts and liner surfaces prevented possible solid-to-solid contact in the entire duration of 720-degree crankshaft rotation, which corresponds to four piston strokes.Copyright

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

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.Copyright

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

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.Copyright

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

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.Copyright

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

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.Copyright

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

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.© 2010 ASME

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

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.Copyright

Verifying experiment for automated design of mechatronic systems using Bond-Graph modelling and simulation and genetic programming

All modern dynamic engineering systems can be characterised as mechatronic systems. The multi-domain nature of a mechatronic system makes it difficult to model using a single modelling technique over the whole system as varying sets of system variables are required. Bond-Graphs offer an advanced object-oriented modelling and simulation technique. They are domain independent allowing straight forward and efficient model composition, classification and analysis. Bond-Graph model of the mechatronic system can be directly simulated on a digital computer using simulation software such as 20-Sim© and Modelica© graphically or manipulated mathematically to yield state equations using a simplified set of power and energy variables. The simulation scheme can be augmented to synthesise designs for mechatronic systems using genetic programming as a tool for open-ended search. This research paper presents results of an experiment conducted to verify a unified approach developed by combining Bond-Graph modelling and simulation with genetic programming for automated mechatronic system design. A comprehensive review of various aspects of the physical modelling paradigm along with the concept and development of automated design and the methodology is also included.