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Man builds 100mpg engine using 200-year-old technology

By Kelly Hodgkins June 15, 2016

Josh "Mac" MacDowell of San Antonio Texas had a brilliant idea. He took a Stirling engine, a type of engine developed 200 years ago, and added some 21st-century technology to it. The result is a hybrid electric car so efficient that you never have to stop to recharge, reports Houston's KHOU11.

The centerpiece of MacDowell's innovation is the Stirling engine, which was created in 1816. The closed-cycle air engine uses the expansion of hot air and the compression of cold air to generate the power needed to drive an engine. Unlike steam engines which utilize a similar principal, the Stirling engine has an internal regenerative heat exchanger that keeps the hot and cold air at the correct temperature. This recycling feature boosts the engine's efficiency to a whopping 50 percent. For comparison, a standard internal combustion engine operates only at 14 percent efficiency.

Though mechanically sound, the Stirling engine never caught on in the 1800s, with most businesses choosing to use steam engines for their industrial applications. NASA even experimented with the engine in the early 1980's, and was able to achieve 54 miles per gallon, but the Space Agency never went any further with the technology. MacDowell borrowed one of these Stirling engines from NASA and began experimenting with it to see if he could use the regenerative engine with 21st-century automotive know-how.

MacDowell coupled the engine with existing hybrid technology, creating a system that will deliver 58 miles per gallon to a Ford F-150 and at least 100 miles per gallon in a smaller SUV. In his model, the Stirling engine runs at a fixed RPM generating electricity that is used to charge the batteries, which drive motors that propel the vehicle.

Using this thermopile technology, a Stirling-powered vehicle can drive at highway speeds without having to recharge. MacDowell also redesigned the Stirling engine to have the dimensions and appearance of a standard four-cylinder engine, making it compatible with existing automobiles. His idea was so brilliant that Texas A&M University became involved in the project, providing MacDowell with technical expertise and a testing environment to aid in the development of the engine.

To showcase his original engine, MacDowell intends to drive an SUV across the country on less than 40 gallons of gasoline. He also plans to submit his laboratory findings to the Texas Transportation Institute, which will verify his 100 miles per gallon claims. Once proven and tested, MacDowell believes his idea will revolutionize the hybrid engine industry leading to the eventual end of the internal combustion engine. Stay tuned.

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"Phase I Results from the Stirling Powered Vehicle Project funded by NASA


Ten months of operation were with Air Force personnel at Langley Air Force Base. VA, where over 1100 hr and 4000 mi were logged on the Langley flight line. The Stirling-powered van was operated on unleaded gasoline. JP-4 aircraft fuel, and diesel fuel at Langley Air Force Base. Two months of operation were completed with Deere & Company personnel in the Moline. IL area where over 175 hr and 2650 mi were logged on a Deere mail delivery route.

The Air Force provided a 1986 General Motors (GM) multistop (delivery) van (Fig. 1) powered by a standard 6.2-L (379-in3) V-8, diesel engine (145 hp (108.8 kW) at 3600 rpm). Curb weight of this vehicle is 6800 lb (2677 kg), with a maximum gross vehicle weight (GVW) of 8600 lb (3386 kg). Engine specifications and a power and torque curve are shown in Table 1 and Fig. 2. When the GM multistop van arrived at MTI, it was driven approximately 1100 mi to break in the drivetrain to ensure that the vehicle was sound. After the vehicle break-in was completed, the diesel engine was removed and a Mod I Stirling engine mockup was installed to determine what modifications would be required. The only major alteration required was a cutout in the front crossmember. This modification was needed so that the engine and transmission could be properly installed and aligned.

Oil samples were taken 10 times during the one-year evaluation period and sent to Deere & Company for detailed analysis. No degradation of the oil was noted and Air Force operators and maintenance personnel observed that the oil appeared to be in "like new" or "virgin" condition.

Fuel economv for the Stirling- powered van was reported bv the Air Force to be 6.3 mpg with all fuels used during the 10-month evaluation period. Fuel economy numbers include fuel usage for both the gas-fired, front window defogger and the rear-compartment heating system. This compares with an average of 4.3 mpg for four gasoline-powered vans and 8.1 mpg for nine diesel-powered vans used at Langley in similar missions during the same period.

The 75-hp automotive Stirling engine, although underpowered for the Air Force multistop, has demonstrated that it has the potential to be a viable multifuel engine for lightduty trucks and vans of the future.

As of January 1988. seven experimental. first-generation. Mod I automotive Stirling engines CASE'S) were built and operated in test cells and vehicles for over 18 000 hr."