200-Year-Old NASA-Tested Engine May Be the Key to 100 MPG SUVs

Texas inventor builds a hybrid powertrain using a Stirling engine.


In his attempt to develop the next generation of experimental powertrains, Texas inventor Josh MacDowell has gone way back in time. By pairing modern hybrid batteries and electric motors with a 200-year-old design called a Stirling engine, MacDowell claims to have created a a range-extended electric vehicle powertrain he says gets 100 miles per gallon in a small SUV. And he's already nabbed a patent for it.

Created by Scottish minister Robert Stirling in 1816, the Stirling engine is a closed-system engine that uses internal differences in air temperature to move two pistons, which can then perform mechanical work.According to Houston’s KHOU 11 News, instead of using the Stirling to perform work, MacDowell attached a thermopile—a linked series of conductors that can generate voltage from differences in temperature—to the business end of the engine. So the Stirling powers the thermopile, the thermopile creates voltage to charge the batteries, and the batteries power the electric motors that turn the wheels.

One of the biggest benefits to MacDowell’s Stirling is its thermal efficiency, which reaches about 50 percent thanks to an internal regenerative heat exchanger. Even the most finely tuned gasoline engine, like that in a Toyota Prius, can only reach 40 percent thermal efficiency.

The inventor says he can get “at least 58 miles per gallon” out of a Ford F-150 right now. After he’s finished shrinking the hybrid power unit and installing it in a smaller SUV, he predicts a return of 100 mpg. He plans to prove it with a cross-country drive from the East Coast to California using less than 40 gallons of gas, after which he’ll have the numbers verified at both the Texas A&M Transportation Institute and the independent, non-profit Southwest Research Institute in San Antonio.

It may all sound pie-in-the-sky, but at least one group of smart people at Texas A&M like what MacDowell is doing. Dr. Mirley Balasubramanya described the novel power unit as "a wonderful idea,” and his department is helping the inventor with testing and technical expertise.

MacDowell is hardly the first forward-looking inventor to play around with Robert Stirling's mechanical masterwork. Segway inventor Dean Kamen is a fan of the engine; he put one in the Th!nk electric car in 2008, created a Stirling-powered hybrid scooter in 2009, and has spoken to the New Hampshire government about trying to use a Stirling engine to run a building’s HVAC. And the good folks at NASA, who provided MacDowell with his Stirling, experimented with the engine in the Seventies and Eighties. The space agency used the technology to squeeze 54 miles per gallon out of a Dodge pickup, only to walk away from the project...because gas was so cheap.