5 Stroke Engine

Our objective with the 5-stroke engine is to develop a gasoline engine with fuel consumption and emission levels comparable to that of current diesel engines, without the serious problem of particulate and NOx emissions that plague diesels.

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 valvegear with the HP camshaft running at 0.5 x crank speed and the LP camshaft running at 1 x crank speed. The engine is also turbocharged to increase the engine rating.

5-stroke performance figures

Engine capacity 700cc (turbocharged)

Peak power 130 bhp @ 7000 rpm

Peak torque 166 Nm @ 5000 rpm

Fuel consumption of only 226 g/kWh



Advantages of the 5-stroke concept

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

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

Minimised pumping work due to the downsizing effect from highly rated firing cylinders.

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

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

The fuel consumption does not rise as rapidly with increasing BMEP, as retarding rejects more energy into the expansion cylinder.

The engine uses 100% conventional technology and so requires no new manufacturing techniques.

Principle of operation

The 5-stroke concept engine utilises two fired cylinders (High Pressure - HP) operating on a conventional 4-stroke cycle which alternately exhaust into a central expansion cylinder (Low Pressure - LP), whereupon the burnt gases perform further work. The LP cylinder decouples the expansion and compression processes and enables the optimum expansion ratio to be selected independently of the compression ratio.

Running of the concept engine has produced impressive fuel consumption readings over a very wide operating range. This is because at the onset of knock a greater percentage of work can be extracted in the LP cylinder, giving a degree of self compensation.