Lotus Engineering will display a single-cylinder research engine monoblock demonstrating the architecture ofthe Omnivore engine concept at the upcoming 79th International Geneva Motor Show. The Omnivore was designed in collaboration with Queen’s University Belfast and Orbital Corporation Limited Australia for high thermal ef?ciency when fueled on any alcohol-based fuel or gasoline. It features an innovative variablecompression ratio system and uses a two-stroke operating cycle with Orbital FlexDI direct fuel injection. It isideally suited to ?ex-fuel operation with a higher degree of optimization than is possible with existing fourstroke engines, according to Lotus.
The engine concept features a monoblock construction that blends the cylinder head and block togethereliminating the need for a cylinder head gasket, improving durability and reducing weight. In this case, theapplication of a monoblock is facilitated by the absence of the requirement for poppet valves. A novel charge trapping valve in the exhaust port allows asymmetric timing of exhaust ?ow and continuous variation of theexhaust opening point.
“The absence of poppet valves in two-stroke engines makes the incorporation of a variable compressionratio system relatively straightforward. Our research into these systems on four-stroke engines has led us tothe conclusion that while thermodynamically it is a desirable technology to incorporate, practically it is verydif?cult, particularly taking into consideration production feasibility. This two-stroke engine could solve these practical dif?culties and simultaneously permits a much larger range of compression ratio adjustment, withthe potential to perform at a much higher ef?ciency when running on renewable fuels.”
—Geraint Castleton-White, Head of Powertrain at Lotus Engineering
The variable compression ratio is achieved by the use of a puck at the top of the combustion chamber. This system moves up and down affecting the change in geometric compression depending on the load demands on the engine. The Orbital FlexDI fuel injection system produces ?ne in-cylinder fuel preparation irrespective of fuel type, and together with air premixing allows ef?cient two-stroke combustion and low-temperaturestarting, while offering singular opportunity for advanced HCCI control. With sponsorship from DEFRA/DECC and DOE NI through the Renewables Materials LINK program, Lotus Engineering is currently in the ?nalstages of commissioning the Omnivore single-cylinder research engine.
Source: http://www.greencarcongress.com/2009/02/lotus-engineeri.html