Lotus Omnivore two-stroke direct injection engine unveiled
Lotus Engineering, the descriptively named automotive consultancy arm of Lotus Cars, has developed a single-cylinder two-stroke motor designed to run on alcohol-based renewable fuels. The engine, called Omnivore, might sound like something that would power a motorcycle, but it's actually intended for lightweight cars.
The Omnivore concept features a variable compression ratio system and uses a two-stroke operating cycle with direct fuel injection. The engine concept features a monoblock construction that blends the cylinder head and block together eliminating the need for a cylinder head gasket, improving durability and reducing weight. A novel charge trapping valve in the exhaust port allows asymmetric timing of exhaust flow and continuous variation of the exhaust opening point.
Lotus claims the Omnivore is ideally suited to flex-fuel operation with a higher degree of optimization than is possible with existing four stroke engines. The variable compression ratio is achieved by the use of a puck at the top of the combustion chamber. This simple, yet effective system moves up and down affecting the change in geometric compression depending on the load demands on the engine.
The motor uses the Orbital FlexDI fuel injection system which produces fine in-cylinder fuel preparation irrespective of fuel type, and together with air pre-mixing allows efficient two-stroke combustion and low-temperature starting, whilst offering singular opportunity for advanced HCCI control.
"The absence of poppet valves in two-stroke engines makes the incorporation of a variable compression ratio system relatively straightforward," said powertrain development boss Geraint Castleton-White. "Our research into these systems on four-stroke engines has led us to the conclusion that while thermodynamically it is a desirable technology to incorporate, practically it is very difficult, particularly taking into consideration production feasibility. This two-stroke engine could solve these practical difficulties and simultaneously permits a much larger range of compression ratio adjustment, with the potential to perform at a much higher efficiency when running on renewable fuels."
The Omnivore program is another step in Lotus' research into the combustion processes involved in running an engine on mixtures of alcohol based fuels and gasoline, which included the Lotus Exige 270E Tri-fuel, unveiled at the International Geneva Motor Show in 2008