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This paper details an investigation of the output performance of an externally scavenged, single cylinder, two-stroke cycle engine. The engine was of the loop scavenged type with scavenge air supplied by a crankshaft driven supercharger. The main emphasis was to investigate the effects of exhaust and transfer port timings and also to evaluate the effectiveness of different supercharger drive ratios. The engine was run using two different fuel systems; one being a high pressure liquid system injecting directly into the cylinder head and the other being a low pressure liquid system injecting into the intake system. Provision was provided for four different timing edges for both exhaust and transfer ports. In each configuration the engine was performance tested over a range of operating conditions while the fuel efficiency, brake specific emissions and air flow characteristics were recorded.

The gas exchange process of the two-stroke engine is such that the flow of fresh air into the cylinder and exhaust gas out of the cylinder occur substantially together. It is therefore the case that not all of the air delivered will be trapped during this scavenge process. Extensive research has already been conducted into optimising the porting layouts of two-stroke engine cylinders. One of the techniques developed at The Queen's University of Belfast for evaluating scavenging is a unique experimental method described as the ‘single cycle scavenge test’. Although the test does not reflect the actual scavenge process in a firing engine, it is a sufficiently useful procedure to have become an industrial standard for scavenge evaluation. This paper discusses the application of that test procedure in the development of a multicylinder, externally scavenged, two-stroke automotive engine.