As I wrote in Thursday’s Times, several start-ups backed by Silicon Valley venture capital firms are developing a new type of internal combustion engine that promises a striking boost in fuel economy while reducing greenhouse gas emissions.

It sounds a bit too good to be true, but the companies have had their claims verified by independent firms, and some of them have signed licensing deals with major engine manufacturers.

The start-ups that I profiled – Achates Power, EcoMotors and Pinnacle Engines – all are building variations on what is called an opposed piston engine. Such engines do away with heavy cylinder heads that serve as combustion chambers in conventional engines. Instead, the space between two opposing pistons forms the combustion chamber where fuel is ignited.

That makes opposed piston engines lighter and cheaper to make. And because opposed piston engines have a greater power density, they waste less energy as heat and thus operate more efficiently.



“The technology is viable,” said Dean Tomazic, vice president of FEV, an engineering company in Auburn, Mich., that has tested opposed piston engines to verify their developers’ claims. “It is obviously a completely different concept compared to conventional engines.”

Athough such engines were used in the mid-20th century as power plants for ships and World War II-era fighter planes, they were long considered too expensive and impractical for automotive use.

Pinnacle, based in San Carlos, Calif., is developing a four-stroke, gasoline opposed piston engine. One of Pinnacle’s key innovations is a sleeve valve invented by the company’s founder, Monty Cleeves, that helps ensure that energy is used for propulsion rather than wasted as heat.

Mr. Cleeves said that Pinnacle’s engine could run on a variety of fuels, including compressed natural gas and ethanol without a loss of performance experienced in conventional engines.

He has kept the start-up in stealth mode for nearly four years, operating from a small unmarked office and garage a few miles from where Tesla Motors developed its electric Roadster sports car.

Earlier this month, Mr. Cleeves gave me a peek at a prototype of the Cleeves Cycle engine being tested at engine factory in my hometown of Berkeley, Calif. (Who knew?)

Pinnacle has signed a deal to license its technology to a major Asian scooter maker that it declined to identify. The one-cylinder, 15-horsepower engine connected to a maze of wires and tubes dangling from the ceiling of Hasselgren Engineering is larger than the model planned for production.

That engine will be 30 percent more efficient than conventional scooter engines while emitting fewer pollutants, said Mr. Cleeves, noting that performance has been verified by FEV.

“India, for instance, is well behind the rest of the world in emission standards because the costs for implementation are high,” said Mr. Cleeves, who spent his career in the computer chip industry. “We end up making it so they can put in better emissions standards without raising the cost of the vehicles at all.”

“It’s a huge win for public health in the developing world,” he added.

The scooter engine is scheduled to come to market in early 2013. Pinnacle is also developing a multicylinder automotive version that software simulations show will be up to 50 percent more fuel-efficient than conventional gasoline engines, executives said.

The company is seeking a federal grant to speed development of the car engine. If Pinnacle does not obtain the aid, executives estimate the engine would be ready for production in 2016.

Dr. Tomazic said the impact of opposed piston engines remains to be seen.

“Opposed piston engines will find their initial applications as niche products and slowly make their way into the market,” he said. “The industry is really competitive, and everyone is looking for good technology that they can get cheaply and meet customer demands.”