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Lotus to Introduce Range Extender Engine

The Lotus 1.2-liter, 3-cylinder Range Extender engine with integrated electrical generator. Click to enlarge.

Lotus Engineering will unveil its Range Extender engine at the 63rd Frankfurt International Motor Show next week. In a series hybrid vehicle, the Range Extender engine is attached to an electricity generator and provides an efficient source of energy to power the electric motor directly or charge the vehicles battery. The battery can also power the electric motor which enables the design of a drivetrain that has low emissions, optimized performance and acceptable range.

The Lotus three-cylinder 1.2 liter Range Extender engine is optimized between two power generation points, giving 15 kW of electrical power at 1,500 rpm and 35 kW at 3,500 rpm via the integrated electrical generator.

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.

Specifications of the Lotus Range Extender Engine
General 1.2-liter 3-cylinder with 2 valves per cylinder, SOHC
Construction Monoblock with integrated exhaust manifold
All aluminum
Balance shaft (optional)
Direct-coupled generator
Bore and stroke 75.0mm x 90.0 mm
Compression ratio 10:1
Maximum power 35 kW (47 bhp) at 3500 rpm via integrated electrical generator
Peak torque 107 N·m at 2500 rpm
Maximum BMEP 11.2 bar
Maximum engine speed 3500 rpm
Fuel system Port fuel injection, Lotus EMS
Fuel 95 RON ULG, ethanol or methanol
Dry weight 56 kg


Multi-Modal Commuter Dude (formerly known as Bike Commuter Dude)

Perhaps this could be of interest on future Tesla models, seeing as Lotus already produces their chassis. With some Tesla parts being used for the series hybrid approach, a very cost effective joint venture could perhaps be in the works.


I think this genset would come close to meeting the requirement of a self-contained, mobile range extender bumper trailer for use by BEVs on long distance trips.

The idea is that BEVs would be used mostly for battery only trips of less than 100 miles on a daily basis. When long trips are desired, hook on the trailer, attach the electronic and power cables, fill the unit with fuel and you are set to go. This could be a dealer rental device or an option; which ever meets the driver's needs.

The main advantage of this idea is the BEVs doesn't need to carry any more battery weight or the extra weight of an on-board ICE on daily trips which should improve the efficiency of the car.


This is great news. I expect to see quite a bit of competition in this area eventually. I wonder what the specific fuel consumption will be at both speeds. That's what really determines your mileage over long trips.


This seems small enough to use an optional power module space in new EV vehicles.

The REE could be rented/inserted for cross-country travel or range anxiety concerns.

Henry Gibson

This unit promotes most of the advantages that have been mentioned in prior posts. The multiple fuel use is a great advantage since methanol and butanol have very long storage lives for when the extender is not needed. It is too large for most users. It would have been better for many puposes just to have used the OPOC design for less weight. TZERO demonstrated the trailer range extender. Why are there three pistons instead of one to run a generator? Why are such low RPMs used to power a generator. A dynamic mass balancer could deal with vibrations and be reliable for fewer parts. This is probably a better range extender than the VOLT one so GM should abandon all work on theirs to save taxpayer money. For this power range a Capstone turbine could be used with only one moving part and no need for catalytic converters or a cooling system or a lubrication system. The electrical efficiency could have been mentioned in Kilo-Joules thermal per kilowatt hour electric, but there is yet no way to compare it to a Capstone turbine.

In truth, most car users would rarely use a range extender so the efficiency of them is of low concern.

A hydraulic hybrid would have most of the low fuel use advantages without the high cost of electric motors, electronic drives and batteries. Never the less; the Plug-in-Hybrid is one of the most efficient ways to reduce oil consumption and CO2 release. Coal to liquid is the fastest way to reduce oil use. ..HG..

Henry Gibson

Perhaps the AURAGEN could have been incorporated for weight savings. ..HG..


Hope that this will be one of many common sense light weight gensets for future PHEVs range extenders.

Future PHEV/BEV configuration could offer a similar genset as a plug-in (removable) optional unit that could be replaced with a second battery pack to change a PHEV into a BEV (or visa versa) when batteries price come down.


How small could these things potentially get? I see this is for quite a large vehicle but what about the potential for smaller EVs such as the Loremo?


How small could these things potentially get? I see this is for quite a large vehicle but what about the potential for smaller EVs such as the Loremo?


Why a 10:1 compression ratio? The big benefit of a range extending engine is that it's not limited to traditional 'road connected' engine requirements for throttle reponse, low down torque etc. They should have made it a 15:1 Miller or Atkinson cycle to increase the thermal efficiency from ~28% to ~38%. Big gains in fuel economy from a relatively simple approach.

Will S

Exactly the direction automakers should be going, as a complement to BEV production. Hats off to Lotus.


What clett said.

One stat is very obvious in the table at the end... due to its absence.  That is the BSFC.  This engine is over-square and runs slow, which is good, but the thermal efficiency is one of the most important specs and it isn't given.

I'd like to see some extreme efficiency measures.  Things like a direct-injection Atkinson cycle with Comprex pressure-wave supercharging to make up the volumetric efficiency and recycle the exhaust pulse energy.  If you have an engine that only runs at 2 speeds you can do this, so the system can squeeze the absolute maximum out of every bit of fuel it's forced to burn.  Why waste anything?

Henry Gibson

Driving a car at high speeds on motorways defeats any efficiency that is built into an automotive engine. ..HG..

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