Two Stroke Engines - The Lotus Approach

The recent interest in two-stroke engines for automotive use has produced powerplants of such divergence that as yet, no clear outlook on a likely design is evident. The only common similarity between all the published engines is direct fuel injection. Whilst this is undoubtedly necessary, the effects of exhaust and scavenging systems play a significant role in the overall performance of the engine. This paper initially describes a valve mechanism providing infinitely variable control of the exhaust port opening point, together with the ability to effectively close the exhaust port at the end of the scavenge period. Such a valve has been tested in a single cylinder, 400 cc loop scavenged engine giving encouraging results. The concept of a rotary inlet valve, situated in the cylinder head is also discussed with a view to achieving uniflow scavenging.