Flow and heat transfer modelling of an automotive engine lubrication system
This dissertation documents the thermodynamic and fluid mechanic analysis of an engine lubrication system. A comprehensive thermofluid computer model was developed to provide a flexible design analysis tool for the accurate prediction of oil pressures, flow rates and temperatures at any point within any lubrication system. Technical and financial support for the study was provided by Jaguar Cars. A comprehensive literature review revealed that the past research in this field had concentrated on either the thermofluid analysis of the lubrication system by engine testing, or the detailed analysis of individual components. A small number of computer models were developed for the flow analysis of the whole lubrication system. However, these models had limited heat transfer prediction capabilities, some requiring measured engine temperature data, and were not flexible enough to be employed as design tools. The objective of this study was to develop a flexible steady-state thermofluid design analysis tool, by integrating a flow analysis approach with a detailed analysis of the heat transfer within the engine block. Mathematical models of the thermofluid behaviour of the lubrication system components were developed and were implemented in a suite of FORTRAN computer programs which formed the design analysis package. A simple, linear flow model was initially developed to represent the system with a combination of laminar pipes, pumps, filters, journal bearings, crank-shaft transfer holes and cam bearing transfer holes. The linear program provided a rapid analysis tool, but the accuracy of the results were limited by the simplified flow characteristics of the system components. A more comprehensive and flexible non-linear flow model was developed, which solved for the unknowns with an iterative technique. Additional component models with non-linear flow characteristics, such as turbulent pipes, annular pipes, strainers, and oil coolers, were developed. The non-linear solution technique was proven to be robust and flexible and was subsequently used in all the analysis programs. The heat transfer to the oil within the pressurised part of the lubrication system is modelled by the heat transfer program. The engine block temperatures are calculated by the engine block program. This program accounts for the heat transfer to the oil splashed on to the internal surfaces of the engine. The engine geometry is represented by a series of block elements and modelled as a nodal resistance network. This capability has particular importance during the design stage, rapidly providing an estimate of the temperature profile through the engine block, results which were previously only available from expensive and slow FEA models. It was shown that both the Jaguar AJ6 and V8 engine lubrication systems could be analyzed in great detail. Engine tests showed that the predicted flow rates, pressures and temperatures were in excellent agreement with measured values. The overall accuracy of the results induced a high degree of confidence in the thermofluid model. The final analysis package was proven to be easy to use, robust, rapid, flexible and accurate. The design analysis package, developed during the course of this study, represents a unique stand-alone simulation tool which can rapidly analyze any engine lubrication system configuration. This package provides a valuable analysis tool which can be used to optimise system designs at the initial design stage and the diagnosis of performance problems during the development phase. Parametric studies can be easily carried out on the lubrication system and engine block configuration to identify areas which can enhance heat transfer to the oil. The steady-state analysis package forms an excellent platform for the development of a full transient model. This would allow a detailed analysis of the lubrication system during engine warm-up, with the aim of reducing engine emissions and determining minimum oil requirements.