At the 79th Geneva International Motor Show next week Lotus will be exhibiting the single-cylinder research engine monoblock, Omnivore.
The Omnivore was designed in collaboration with Queen’s University Belfast and Orbital Corporation Limited Australia for high thermal efficiency regardless of whether an alcohol-based fuel or petrol is used. It features an innovative variable compression ratio system and uses a two-stroke operating cycle with Orbital FlexDI direct fuel injection. It is ideally suited to flex-fuel operation with a higher degree of optimization than is possible with existing four stroke engines, according to Lotus.
The multi-fuel one-cylinder can drink any alcohol or gasoline-based fuel
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. In this case, the application 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 flow and continuous variation of the exhaust opening point.
“The absence of poppet valves in two-stroke engines makes the incorporation of a variable compression ratio system relatively straightforward” said Geraint Castleton-White, Head of Powertrain at Lotus Engineering.
“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 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 fine in-cylinder fuel preparation irrespective of fuel type, and together with air premixing allows efficient two-stroke combustion and low-temperature starting, while offering singular opportunity for advanced HCCI control.
Lotus believes that C02 emissions would be greatly reduced towards the ideal of zero if the motor industry were to embrace alcohol-based fuels.