The Lotus Range Extender engine features an innovative architecture comprising an aluminum monoblock construction, integrating the cylinder block, cylinder head and exhaust manifold in one casting. This results in reduced engine mass (56 kg/123 lbs), assembly costs, package size and improved emissions and engine durability.

The engine uses an optimized two-valve port-fuel injection combustion system to reduce cost and mass and, in line with Lotus Engineering’s research into renewable fuels, can be operated on alcohol-based fuels or gasoline.

In addition to the cost-advantage of its engine design, the Range Extender’s high efficiency and low mass will enable the downsizing of expensive batteries while maintaining vehicle efficiency and range, according to Lotus. The engine has been designed using production methodologies and the parts procured from low volume potential production suppliers, offering a fast route to market for original equipment manufacturers wanting to source a dedicated range extender for series hybrid vehicles.

Lotus developed the Range Extender engine as part of the ‘Limo-Green’ project funded by the UK’s Technology Strategy Board, a collaboration between Lotus Engineering, Jaguar Cars Ltd, MIRA Ltd and Caparo Vehicle Technologies, demonstrating a large, lightweight, prestigious executive sedan with less than 120 g/km CO₂ emissions. (Earlier post.)

Key features of the Range Extender engine include:

• Monoblock. The Range Extender features a novel engine architecture incorporating a monoblock construction that blends the cylinder head and block together eliminating the need for a cylinder head gasket, improving durability and reducing weight. Approximately 17 parts are eliminated using this approach and the water jacket is better optimized.

• Integrated Exhaust Manifold. Lotus Engineering designed and developed a new advanced cylinder head design featuring an integrated exhaust manifold. The production-ready technology can significantly reduce manufacturing costs, emissions and weight. An integrated exhaust manifold has potential to:

  • Reduce parts count: 18 fewer components resulting in lower inventory, production, logistics and aftermarket costs;
  • Reduce weight: total system mass reduction resulting from elimination of separate exhaust manifold;
  • Improve engine durability.

• Generator. Attached to the engine via the crankshaft, the generator sustains vehicle operation beyond the range provided by the batteries.

• Additional Benefits. The Lotus Range Extender engine generates a reduction in emissions through faster light-off of the close-coupled catalytic converter with a reduction in heat loss between the exhaust port and catalyst inlet. Engine operating range is optimized to deliver more efficient running, which also aids underhood thermal management.

  Utilization of the monoblock construction results in an assembly cost reduction, while there is also a reduced catalyst loading requirement because less heat is lost on engine start-up between the exhaust port and catalyst inlet.

  Increased vehicle integration flexibility is achieved because of the reduction in mass and the reduced package size leads to reduced space requirements. Particular emphasis has also been placed on the coupling of the generator and NVH signature.