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The paper describes the principal features of Omnivore, a spark-ignition-based research engine designed to investigate the possibility of true wide-range HCCI operation on a variety of fossil and renewable liquid fuels. The engine project is part-funded jointly by the United Kingdom's Department for the Environment, Food and Rural Affairs (DEFRA) and the Department of the Environment of Northern Ireland (DoENI). The engineering team includes Lotus Engineering, Jaguar Cars, Orbital Corporation and Queen's University Belfast. The research engine so far constructed is of a typical automotive cylinder capacity and operates on an externally-scavenged version of the two-port Day 2-stroke cycle, utilising both a variable charge trapping mechanism to control both trapped charge and residual concentration and a wide-range variable compression ratio (VCR) mechanism in the cylinder head.

Washcoat sintering and substrate meltdown have traditionally been the principle deactivating mechanisms of catalysts fitted to two-stroke engines. The reduction of the excessively high HC and CO levels responsible for these effects has therefore been the focus of considerable research which has led to the introduction of direct in-cylinder fuel injection to some larger versions of this engine. However, much less attention has been paid to the effects of oil and its additives on the performance and durability of the two-stroke catalyst. The quantity of oil emitted to the exhaust system of the majority of two-stroke engines is much greater than in four-stroke engines of comparable output due to the total loss lubrication system employed. The fundamental design of the two-stroke also permits some of this oil to ‘short-circuit’ to the exhaust in a neat or unburned form.

Engineers dealing with the two-stroke cycle engine have always sought to find a scavenge flow simulation process which will allow for the development of an existing engine or provide information for the design of a new power unit. Many schemes put forward have been found wanting in some manner, although in recent times the method proposed by Jante has been shown to be very effective and to that end this paper provides further evidence. In this publication a new version of the old idea of simulating scavenging by a liquid flow approach is presented, an apparatus described and test results given for six cylinders of one two-stroke cycle engine. These six test cylinders have dissimilar scavenge flow characteristics while retaining similar dynamic flow parameters and are tested under firing conditions for the usual performance characteristics as well as for scavenging and trapping efficiencies; they are also tested using the Jante motoring method for their scavenge flow behaviour.