Stirling Engine: External Combustion Efficiency

One of the most unusual looking cars at this year’s Shell Eco-marathon Europe was testing out one of the oldest concepts for harnessing energy for motion: the Stirling heat engine.

Team Schluckspecht from the University of Applied Sciences, of Offenburg, Germany, designed a vehicle that relied on external heating and cooling to drive pistons. The Stirling engine concept, named after Scottish inventor Robert Stirling who introduced his model in 1816, is sometimes called an external combustion engine because heat is applied from outside the engine.

Unfortunately, the team’s vehicle did not pass the qualifying tests for the competition that ended Saturday in Rotterdam. The car was too heavy and too high, due to the system coils on its roof. But the vehicle did complete some test runs to try out a concept that the students think has promise for future energy systems.

Michael Dold, who is earning his master’s degree in energy conversion at the school, explains one of the Stirling engine’s great advantages is that it can be used with any fuel source. (Team Schluckspecht powered its vehicle on ethanol.)

U.S. government researchers who studied the Stirling engine note that its development was hampered in part because materials that could withstand the high temperatures were not available in the early years of experimentation. Also, the engines were slow to heat up, and couldn’t compete with the spark-ignition engine. Still, automakers in Detroit tested Stirling engines during the oil crises of the 1970s, and a few years ago, Segway inventor Dean Kamen also experimented with the concept. Because of its extreme efficiency, quiet, and fuel versatility, many innovators–including the Offenburg students–think the Stirling engine may have a future in providing energy.