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The performance of two-stroke, high specific output engines, is largely dependent on the exhaust system. This paper describes an experimental study on the effect of each of the exhaust pipe sections on the actual engine performance. The exhaust system has been designed with interconnecting flanges that allow the various sections to be bolted together for testing on a dynamometer. This allows numerous combinations of various section designs to be evaluated. In an effort to understand the exact mechanisms involved in the pressure wave action within the engine, several pressure transducers have been located in the intake, crankcase, cylinder and exhaust.

Coefficient of discharge for a particular flow discontinuity is defined as the ratio of actual discharge to ideal discharge. In an engine environment, ideal discharge considers an ideal gas and the process to be free from friction, surface tension, etc. Discharge coefficients are widely used to monitor the flow efficiency through various engine components and are quite useful in improving the performance of these components. In modelling the flow through internal combustion engines it is equally important to have accurate values for coefficients of discharge through the combinations of valves, ports and ducts. It is especially important when modelling high performance two-stroke engines, due to the relatively high flow rates and the rapidly changing flow directions. Such an engine relies on the plugging pulse from the tuned exhaust system to ram escaped fresh charge back into the cylinder, prior to exhaust port closure.