Three-cylinder, five-stroke engine provides fuel and emissions savings
7 August 2009

Ilmor Engineering has developed an innovative 130bhp, 700cc, three-cylinder, five-stroke petrol engine that develops the fuel economy of a diesel engine without any of the emissions shortcomings.

The engineering firm, which has a long history working in motorsport and which was previously part-owned by Mercedes when it prepared its F1 engines, has developed the radical road car engine to showcase its engineering ability.

See the Ilmor engine gallery here

The novel design allows the turbocharged engine to achieve a diesel-like expansion ratio on spark ignition, greatly improving fuel consumption but still achieving 122lb ft of torque.

Ilmor says the fuel consumption is better than the latest downsized turbocharged engines on sale. It estimates its engine is at least five per cent more efficient than an equivalent direct injection engine, despite currently running with multi-point injection.

The engine uses two fired four-stroke cylinders under high pressure, which alternately exhaust into a low-pressure central expansion cylinder, which, in a fifth stroke, provides a further expansion process on the exhaust gases.

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Ilmor also says that due to the larger expansion cylinder, the engine balance is the same as a conventional four-cylinder engine.

Ilmor now hopes to develop a second-generation engine for in-car testing, saying a 150bhp unit that is 20 per cent lighter than a standard equivalent engine is achievable.

"There is so much more to come," said Steve O'Connor, Ilmor's engineering manager. "This is just a first concept, and there's plenty of refinements to come.

Ultimately, Ilmor hopes to sell the engine to a major car manufacturer, and says its characteristics make it particularly applicable to use in conjunction with hybrid systems.

"We're looking for a manufacturer to back the idea," said O'Connor, "and the interest centres on its use in a hybrid application, as they tend to need sudden bursts of energy, and that is what this engine does well."

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