|The Lotus Omnivore engine. Click to enlarge.|
Lotus Engineering will display a single-cylinder research engine monoblock demonstrating the architecture of the Omnivore engine concept at the upcoming 79th International Geneva Motor Show. (Earlier post.)
The Omnivore was designed in collaboration with Queen’s University Belfast and Orbital Corporation Limited Australia for high thermal efficiency when fueled on any alcohol-based fuel or gasoline. 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 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. 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.—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 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.
With sponsorship from DEFRA/DECC and DOE NI through the Renewables Materials LINK program, Lotus Engineering is currently in the final stages of commissioning the Omnivore single-cylinder research engine.