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Reed valves are the most common method used to control the intake of fresh air and fuel into the crankcase of a high performance two-stroke engine. While they can be quite simple in terms of mechanical design, their operation is highly dynamic and can be influenced by many other components. Previous publications from The Queen's University of Belfast have shown the derivation of mathematical models and their verification by measurements from a firing engine at relatively high engine speeds, up to 9,500 rev/min. In this present paper, measured and predicted data for delivery ratio and reed tip lift are presented for a 125 cm3, single cylinder engine over a range of speeds up to 12,290 rev/min. Steady flow discharge coefficients are measured and used in the mathematical simulation. Four variations of reed valve material/thickness are investigated in the firing engine. Correlation between measured and predicted delivery ratio is good over the speed range and various reed specifications.

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.

The performance of two-stroke, high specific output engines, is influenced considerably by the ignition timing curve. This paper describes the cylinder pressure analysis of a TZ250B Yamaha racing motorcycle engine. Cylinder pressure data was recorded for compression ratios of 7.8 and 9.0, for a range of engine speeds. The analysis of the cylinder pressure was carried out with computer software written in fortran 77 code.

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.