BMW Turns to Steam to Boost Power, Improve Fuel Economy

By FELIX BAUER | AUTOMOTIVE NEWS

AutoWeek | Published 02/13/06, 1:17 pm et

MUNICH, Germany -- BMW is applying steam-engine technology in an auxiliary drive that the automaker says can boost both power and fuel efficiency in ordinary piston-driven cars.

The automaker is testing a two-stage device called the Turbosteamer on a stationary conventional 1.8-liter engine at BMW headquarters here.

The device works entirely on the waste heat from the engine.

Turbosteamer converts more than 80 percent of the heat energy in the exhaust into usable power, says Raymond Freymann, head of BMW's advanced research and development subsidiary.

BMW could start building production vehicles with the system by the first half of the next decade, Burkhard Goeschel, BMW board member for r&d, said during a briefing.

The system can be used on any combustion engine.

In trials on a test rig, the system when attached to a regular BMW four-cylinder, 1.8-liter Valvetronic engine reduced fuel consumption by 15 percent. It also generated an extra 13 hp and 14.8 pounds-feet of torque.

The concept is hardly new. The first patent for a steam auxiliary drive harnessing exhaust heat was issued in 1914 to Wilhelm Schmidt of Germany.

The sheer size of a heat-recovery system had been the biggest problem. But the Turbosteamer fits in a regular 3-series body.

"All we lose is a bit of ground clearance," says Freymann.

BMW knows that a production version of the Turbosteamer system must provide enough benefit to justify the higher price tag.

Says Freymann: "The clients have to save more fuel than the system's extra cost."

How the system works

BMW's system uses two fluid-circulating systems to recover exhaust heat from the gasoline engine. The primary high-temperature circuit pumps water through a heat exchanger, surrounding the exhaust gases immediately behind the catalytic converter. Water is heated to 1,022 degrees Fahrenheit.

Steam is converted into mechanical energy in an expander and transferred by pulleys to the engine crankshaft.

The steam flows through another heat exchanger and transfers its remaining heat to a second circuit filled with ethanol. This lower temperature system replaces the engine's regular coolant system.

This system also collects heat in a heat exchanger in the exhaust-gas flow. It releases its energy in a second expander unit that transfers the energy to the crankshaft.

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