Paper 3: Non-Steady Flow in Internal Combustion Engine Inlet and Exhaust Systems

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Abstract
Previous work on non-steady flow in exhaust systems has shown that the method of characteristics can be used to predict the flow conditions to a high degree of accuracy. In these calculations the pressure at the inlet port or valve was considered to be constant. Recent work on the effect of pulsating flow on centrifugal compressors has shown the importance of considering non-steady flows in the inlet systems of supercharged engines. Predictions of the non-steady flow in inlet systems, usually based on acoustic theory, have only been accurate in particular cases. In this paper the method of characteristics has been applied to the study of non-steady flows both in the inlet and exhaust systems of internal combustion engines. Comparisons are made between the calculated and experimental results obtained on a multi-cylinder pulse generator. Tests on both single- and two-cylinder units were carried out and measurements of the inlet pipe pressure, exhaust pipe pressure, cylinder pressures and temperatures, and inlet and exhaust mass flows were made. Comparisons between the theoretical predictions and the test results were extremely good; in all the cases the pressures were in close agreement. The inlet predicted mass flows were all within +9 and −4 per cent of the measured flows, the standard deviation being 3·1 per cent. The exhaust mass flows were all within +8 and −12 per cent of the measured mass flows, the standard deviation being 4·3 per cent. It was considered that the method gives reliable predictions of the flow processes in internal combustion engines.

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