January 2, 2011
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With its first prototype Five-Stroke having achieved an impressive fuel consumption figure of 226g/kWh, engine designer and manufacturer Ilmor Engineering is planning a second phase development engine for real-world in-vehicle testing.

Targets for the new engine, which could be suitable for installation for either hybrid or conventional installation, are a Brake Specific Fuel Consumption (BSFC) of better than 215 g/kWh, a 20 percent reduction in weight over existing production engines of a similar output, and a power density of 150 hp/L. Following testing on Ilmor’s dynamometers and detailed analysis of the first prototype powerplant, developments are planned to cylinder capacity, valve gear design, turbo selection, and ancillaries to achieve these figures. No modifications are planned which would require any unconventional or new manufacturing processes, its simplicity and reliance on tried and tested technology being one of the key benefits of the Five-Stroke engine.


The patented five-stroke concept utilizes two fired cylinders operating on a conventional four-stroke cycle, which alternately exhaust into a central expansion cylinder, whereupon the burnt gases perform further work. The additional low pressure expansion cylinder decouples the expansion and compression processes, and enables the optimum expansion ratio to be selected independently of the compression ratio.

The engine uses two overhead camshafts, one is high pressure, the other low pressure. The high pressure camshaft turns at half the crank speed while the low pressure crankshaft rotates at the same speed as the crank.

The high pressure cam works with the outer two cylinders, in the same way a standard four-stroke engine would, but the low pressure camshaft works with the central larger cylinder gathering exhaust flow from the outer cylinders. The engine is designed to be far more fuel efficient than a traditional four-stroke four-cylinder counterpart.


    1. A secondary cylinder provides an additional expansion process enabling extra work to be extracted, hence increasing thermodynamic efficiency.

    2. The engine runs an overall expansion ratio approaching that of a diesel engine ? in the region of 14.5:1

    3. The compression ratio can be reduced to delay knock onset without a reduction in performance.

    4. Because the firing cylinders can be very highly rated, the engine is relatively compact.

The engine concept, which was invented by Gerhard Schmitz, has been developed by Ilmor into a working engine using a rapid prototype cast cylinder head, a machined from solid cylinder block and separate electrically powered oil and water pumps. Two overhead camshafts operate the conventional coil spring valve gear with the HP camshaft running at 0.5 x crank speed and the LP camshaft running at 1 x crank speed. The engine is turbocharged to 3 bar abs.


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