BMW develops steam-assisted drive system for the 3-series
17 December 2005

STEAM-DRIVEN CARS went out of fashion more than 80 years ago, but BMW is experimenting with a steam-powered auxiliary drive that increases power and cuts fuel consumption.

The Turbosteamer uses over 80 per cent of wasted heat from the exhaust and cooling system to produce steam, which helps to drive the crankshaft. The set-up has been tested on a 1.8 four-cylinder petrol engine on a stationary rig, where it improved fuel consumption by 15 per cent and increased power by 13bhp and torque by 15lb ft.

The system works by passing water through a condenser on the exhaust system, and using the generated steam to drive a pulley on the crank via an expander at the front of the engine. A second circuit containing hot water from the cooling system also passes through the condenser, and this drives another crank pulley.

A four-cylinder powerplant was used because it leaves enough room in the engine bay of a 3-series to accommodate the system.

Steam auxiliary drives using a heat recovery system have been around since 1914, but their size has always prevented development. BMW claims it could have a production-ready Turbosteamer within 10 years, and that the finished version could be fitted to any combustion engine.

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Our Verdict

Toyota Verso

Appealing to some, thanks to a fine balance of quality, space and refinement, but rarely thrilling to be in

Find an Autocar car review

Driven this week