Lotus will reveal a one-cylinder version of its new flex-fuel engine concept at Geneva motorshow next week. Pictures and further details of the Omnivore project have been released today, with Lotus claiming its new technology has the potential to significantly increase fuel efficiency for sustainable alcohol-based fuels.
The Lotus Omnivore engine (Ed, ‘omnibibe’ surely?) boasts an innovative variable compression ratio system and two-stroke operating cycle with direct fuel injection allowing it to run on petrol or alcohol-fuels such as ethanol.
Among the new power unit’s unusual features are monoblock construction with combined cylinder head and block, eliminating the need for a head gasket - apparently this improves durability as well as saving weight. Things get a little more technical after that, so we’ll quote the Lotus press release verbatim:
‘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 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,” says Lotus.’
According to Lotus Engineering’s head powertrain boffin Geraint Castleton-White, switching from a four-stroke to a two-stroke operating cycle was the key to successful implementation of the flex fuel concept.
‘The absence of poppet valves in two-stroke engines makes incorporation of a variable compression ratio system relatively straightforward. Research into these systems on four-stroke engines tells us it is thermodynamically desirable, but practically very difficult. This two-stoke engine solves the practical difficulties while permitting a much larger range of compression ratio adjustment,’ he says.
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