Five-stroke engine debut

Ilmor, a UK-based engineering firm, has developed what it claims is the world's first five-stroke combustion engine.

The 700cc turbocharged prototype engine outputs 97kW and 165Nm of torque, which its creators claim is at least five per cent more efficient than a similar displacement direct injection engine. With less than half the capacity of the 1.8-litre engine in the Toyota Prius, the Ilmor powerplant produces 16kW more power.

The five-stroke prototype engine uses multipoint electronic injection as opposed to the more efficient direct injection of petrol, and will be targetting makers of hybrid cars to test its new engine designs. The engine is ostensibly a three-cylinder unit, but the middle cylinder is a special 'low pressure expansion cylinder'.

In a media statement, Ilmor said it "is keen to find a development partner to bring this exciting concept a step closer to production, and to this end is currently in discussion with automotive OEMs and Tier One suppliers, who are showing considerable interest."

Ilmor currently supplies Honda with Indycar engine components and was once part-owned by Mercedes-Benz, when it co-developed F1 powertrains for the German company.

The Northampton-based company also fielded a MotoGP bike in 2006 and 2007 (ridden by Australian Garry McCoy) running an 800cc V4.

After every fourth cylinder stroke (the exhaust stroke), a fifth stroke sends burnt gases to a separate low pressure expansion cylinder. Here's the official explanation from Ilmor:

The patented 5-stroke concept utilises two fired cylinders operating on a conventional 4-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 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 turbocharged to 3 bar abs.