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A method of predicting brake specific fuel consumption characteristics from limited specifications of engine design has been investigated. For spark ignition engines operating on homogeneous mixtures, indicated specific fuel consumption based on gross indicated power is related to compression ratio and spark timing relative to optimum values. The influence of burn rate is approximately accounted for by the differences in spark timings required to correctly phase combustion. Data from engines of contemporary design shows that indicated specific fuel consumption can be defined as a generic function of relative spark timing, mixture air/fuel ratio and exhaust gas recirculation rate. The additional information required to generate brake specific performance maps is cylinder volumetric efficiency, rubbing friction, auxiliary loads, and exhaust back pressure characteristics.

A correlation for total gas-side heat transfer rate has been derived from the analysis of engine data for measured heat rejection rate, frictional dissipation, and published data on exhaust port heat transfer. The correlation is related to the form developed by Taylor and Toong, and the analysis draws on this. However, cylinder and exhaust port contributions are separated. Two empirical constants are fixed to best match predicted to measured results for heat rejection to coolant and oil cooler under steady-state conditions, and also for exhaust port heat transfer rates. The separated contributions also defined a correlation for exhaust port heat transfer rate. The description of gas-side heat transfer is suited to needs for the analysis of global thermal behaviour of engines.

A suite of computer programs for engine thermal analysis and the analysis of thermal interactions with external systems has been developed. Defining an engine design is made particularly simple and the representation generated agrees well with measured data. Engine geometry, mass, and internal coolant volume are determined from a short list of key parameters and the selection of a generic template. Thermal conditions in the engine structure are modelled numerically using the lumped-capacity method. Heat exchange at boundaries with gas, coolant and oil flows are described through sub-models giving good agreement with data for global characteristics of engine behaviour. The effects of spark timing and coolant composition on heat transfer rates are taken into account, as is the effect of frictional dissipation as a heat source. Validation and applications of the model are described.