This paper presents thermodynamic analysis of piston friction in spark-ignition internal combustion engines. The general effect of piston friction on engine performance was examined during cold starting and normal working conditions. Considerations were made using temperature-dependent specific heat model in order to make the analysis more realistic. A parametric study was performed covering wide range of dependent variables such as engine speed, taking into consideration piston friction combined with the variation of the specific heat with temperature, and heat loss from the cylinder. The results are presented for skirt friction only, and then for total piston friction (skirt and rings). The effect of oil viscosity is investigated over a wide range of engine speeds and oil temperatures. In general, it is found that oils with higher viscosities result in lower efficiency values. Using high viscosity oil can reduce the efficiency by more than 50% at cold oil temperatures. The efficiency maps for SAE 10, SAE 30, and SAE 50 are reported. The results of this model can be practically utilized to obtain optimized efficiency results either by selecting the optimum operating speed for a given oil type (viscosity) and temperature or by selecting the optimum oil type for a given operating speed and temperature. The effect of different piston ring configurations on the efficiency is also presented. Finally, the oil film thickness on the engine performance is studied in this paper.

Effect of Piston Friction on the Performance of SI Engine: A New Thermodynamic Approach

In order to obtain greater accuracy in simulation, more sophisticated models are often required. When it comes to the torsional vibration of reciprocating mechanisms the effect of inertia variation is very important. It has been shown that the inclusion of this variation increases model accuracy for both single-cylinder and multi-cylinder engine torsional vibration predictions. Recent work by the present authors has revealed that piston-to-cylinder friction may modify an engine's 'apparent' inertia function. Kinematic analysis also shows that the piston side force and the dynamic piston-to-cylinder friction are interdependent. This has implications for engine vibration modelling. Most modern engines employ a gudgeon pin offset, and there is a growing interest in pursuing large crank offsets; hence, the effect of these on inertia variation is also of interest. This paper presents the derivation of the inertia function for a single engine mechanism, including both piston-to-cylinder friction and crank or gudgeon pin offset, and investigates the effect of each through predictions. The effect of crank offset on the variable inertia function is also verified by experiment.

/pdf/variable-inertia-effects-of-an-engine-including-piston-2jtr6254fu.pdf

Variable inertia effects of an engine including piston friction and a crank or gudgeon pin offset

Predictive modeling of piston assembly lubrication in reciprocating internal combustion engines

Mixed Lubrication and Roughness Surface Effects Application to Piston Rings

The automotive industry has long been searching for efficient ways to improve vehicle performance such as drivability, fuel consumption, and emissions. Researchers in the automotive industry have tried to develop methods to improve fuel consumption and reduce the emission gases of a vehicle, while satisfying drivability and ride comfort issues. Today, by developing computer/software technologies, automotive manufacturers are moving more and more towards modelling a real component (prototype) in a software domain (virtual prototype). For instance, modelling the components of a vehicle’s powertrain (driveline) in the software domain helps the designers to iterate the model for different operating conditions and scenarios to obtain better performance without any cost of making a real prototype. The objective of this research is to develop and validate physics-based powertrain models with sufficient fidelity to be useful to the automotive industry for rapid prototyping. Developing a physics-based powertrain model that can accurately simulate real phenomenon in the powertrain components is of great importance. For instance, a high-fidelity simulation of the combustion phenomenon in the internal combustion (IC) engine with detailed physical and chemical reactions can be used as a virtual prototype to estimate physical prototype characteristics in a shorter time than it would take to build a physical prototype. Therefore, the powertrain design can be explored and validated virtually in the software domain to reduce the cost and time of product development. The main focus of this thesis is on development of an internal combustion engine model, four-cylinder spark ignition engine, and a hydrodynamic torque converter model. Then, the models are integrated along with the rest of a powertrain’s components (e.g. vehicle longitudinal dynamics model) through acausal connections, which represents a more feasible physics-based powertrain model for model-based control design. The powertrain model can be operated at almost all operating conditions (e.g. wide range of the engine speeds and loads), and is able to capture some transient behaviour of the powertrain as well as the steady state response. Moreover, the parametric formulation of each component in the proposed powertrain model makes the model more efficient to simulate different types of powertrain (e.g. for a passenger car or truck).

Acausal Powertrain Modelling with Application to Model-based Powertrain Control

The influence of piston ring lubrication on internal combustion engine performance has received considerable attention for over half-century. Studies show that hydrodynamic lubrication prevails through most of engine cycles, and asperity contact only occurs near the vicinity of dead centers [1][2]. In order to solve the governing equation of lubricant, appropriate velocity and pressure boundary conditions should be incorporated into the lubrication equation - Reynolds equation. While lubricant obeys the no-slip velocity boundary condition, the pressure boundaries at the leading and trail edge of piston ring are related to the chamber and the inter-ring crevice gas pressures. A complete lubrication analysis of piston ring requires an inter-ring gas flow model. In most of existing lubrication models, an isentropic orifice flow model is adopted and the gas flow is assumed to an ideal gas passing through the piston ring end gaps with a constant discharge coefficient [2][3][4][5]. In additional to the flow path of piston ring end gaps, gas also flows through the side-clearance between piston ring and flank groove [6][7][8][9][10]. In this paper, a quasi-Rayleigh narrow-channel gas flow model is proposed by consideration of temperature gradient along radial direction of piston assembly. Piston ring friction force is estimated by a test-rig verified mixed lubrication model [11]. Numerical simulation shows that piston ring friction force and ring axial motion are sensitive to inter-ring gas flow model. The instantaneous indicated mean effective pressure (IMEP) method was adopted here to measure the piston friction during motoring condition. Experimental and numerical results indicate that top ring could contribute about 10% of total power cylinder friction loss.Copyright © 2005 by ASME

Numerical and Experimental Investigation of Piston Ring Friction

This paper presents two piston ring and cylinder liner lubrication models and compares the friction predictions against the experimental results from a corresponding bench test. The first model aims to solve the average Reynolds equation with corrective flow factors, which describe the influence of surface irregularities on the lubricant flow under mixed lubrication condition. The second model takes account of the lubricant film rupture and cavitation. Meanwhile, a stochastic rough contact sub-model quantifies the relation between contact pressure and mean surface separation in both cases. Numerical results on the top compression ring simulation show that both models capture hydrodynamic, mixed, and boundary lubrication regimes, which depend on the real surface topographies of the piston ring and the cylinder liner. Whenever hydrodynamic action is insufficient to maintain the equilibrium position of the ring, the restoring force will be augmented by multi-asperity contacts lubricated by a thin boundary film. Total friction will originate mainly from shearing of viscous lubricant and shearing of asperity conjunctions. The purpose of this modeling effort is to compare both lubrication models to data from an experimental test-rig. This test rig eliminates many of the factors that can make analysis of predictions for real engine operating conditions difficult.Copyright © 2004 by ASME

Friction predictions for piston ring-cylinder liner lubrication

This paper presents a new lubrication model to predict piston ring friction. The average Reynolds equation is adopted to obtain the hydrodynamic component of restoring force against the cylinder liner surface. The dry or boundary lubricated component is derived from Greenwood-Tripp model. The influence of surface irregularities or roughness on the lubricant flow will be described by statistical parameters. Unlike classical piston ring mixed lubrication models, a sideslip rolling friction model is incorporated with contact simulation. Numerical results show that piston ring friction is reduced dramatically by the liner rotation.Copyright © 2005 by ASME

http://www2.eng.cam.ac.uk/%7Empfs/papers/articles/WTC2005/pdfs/t-10/WTC2005-63725.pdf

Theoretical Analysis of Piston Ring Frictional Loss in an Innovative Rotating Liner Internal Combustion Engine

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Papers

Numerical and Experimental Investigation of Piston Ring Friction

Friction predictions for piston ring-cylinder liner lubrication

Theoretical Analysis of Piston Ring Frictional Loss in an Innovative Rotating Liner Internal Combustion Engine