LOTUS ENGINEERING HAS lifted the lid on its latest project, a range-extending petrol engine designed to be used by the next generation of hybrid vehicles.

Intended for use in a series hybrid setup (similar to the upcoming Chevy Volt), Lotus’s new powerplant is essentially a vehicle-borne generator.

Mated to an electrical generator rather than a gearbox, the 1.2 litre three-cylinder engine isn’t used to drive a car’s wheels, but to charge up a bank of batteries when electric power runs low.

The Range Extender engine is designed to work in two output modes, one delivering 15kW of power at a constant 1500rpm and the other generating 35kW at 3500rpm. Both engine speeds have been specifically selected to maximise efficiency, with the higher speed being used to supply more power when the batteries need to be charged faster.

The engine is also much simpler than most petrol engines, being built around a highly simplified monoblock design that combines the cylinder head and crankcase in the one casting.

The exhaust manifold is also integrated into the block, improving emissions, thermal performance and lowering weight. The entire unit weighs just 59kg including its generator, minimising the amount of ‘dead weight’ carried by the vehicle when operating on battery reserves.

The engine is also flex-fuel capable, and can run on 95-octane petrol, methanol or ethanol.

Lotus will be officially debuting its Range Extender engine at the Frankfurt Motor Show next week, however potential production-car applications for the powerplant have yet to be made known. For now though, the Range Extender will see service as a technology demonstrator in the UK Government-funded “Limo Green” project.