An Experimental Investigation into the Effect of Bore/Stroke Ratio on a Simple Two-Stroke Cycle Engine

Paper #:
  • 1999-01-3342

Published:
  • 1999-09-28
Citation:
Thornhill, D., Douglas, R., Kenny, R., and Fitzsimons, B., "An Experimental Investigation into the Effect of Bore/Stroke Ratio on a Simple Two-Stroke Cycle Engine," SAE Technical Paper 1999-01-3342, 1999, https://doi.org/10.4271/1999-01-3342.
Pages:
16
Abstract:
This paper describes an experimental investigation into the effect of bore/stroke ratio on a simple two-stroke engine. This was achieved with a special purpose engine of modular design. The engine allowed four combinations of bore and stroke to be contrived to yield a common swept volume of 400 cm3 with bore/stroke ratios of: 0.8, 1.0, 1.2 and 1.4.Other factors that might affect engine performance were standardised: the exhaust, intake and ignition systems were common, the combustion chamber designs were similar, scavenge characteristics were similar, port timings and time-areas were kept the same, and cylinder and crankcase compression ratios were also kept the same.The most important conclusions were: Engine power was greatest with the compromise bore/stroke ratio of 1.0 or 1.2. Combustion efficiency tended to decrease with increasing bore/stroke ratio. Mechanical efficiency tended to increase with increasing bore/stroke ratio. The specific fuel consumption tended to rise with increasing bore/stroke ratio. The experimental investigation concluded that a square or slightly over square bore/stroke ratio produces an engine with the best brake performance.
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