Another diesel engine start-up comes out of stealth

January is diesel engine month, it seems.

Following announcements from EcoMotors and Transonic Combustion, San Diego's Achates Power has said on its Web site that it's creating a clean, light, fuel-efficient diesel engine.

The company has also received investments from Sequoia Capital, a relative newcomer to energy investments, Rockport Capital Partners and Interwest Partners. (VentureWire has a brief interview with Achates CEO James Lemke.)

Achates has not said how its engine will work, the company has three patent applications on file with the U.S. Patent Office. Two of the patents describe what's known as an opposed piston/opposed cylinder engine. In this type of engine, two pistons sit inside a single cylinder. That makes it different than most other motors where pistons have individual cylinders. (Some car makers have made engines with horizontal pistons, similar to an opposed piston engine, but they have their own cylinders.)

"The opposed-piston engine was invented by Hugo Junkers around the end of the nineteenth century," one of the patent applications states. "In 1936, the Junkers Jumo airplane engines, the most successful diesel engines to that date, were able to achieve a power density and fuel efficiency that have not been matched by any diesel engine since...Nevertheless, Junkers' basic design contains a number of deficiencies."

As a result of the deficiencies and costs, it never went mainstream. But who knows? It could now. EcoMotors, which has received investments from Khosla Ventures, is doing the same thing.

Transonic, meanwhile, has come up with a fuel injection system that increases the pressure inside of diesel engines. Putting Transonic's system into a diesel lets the engine run on regular gas (which is cleaner). Mileage also goes up to 100 miles per gallon. The system sounds similar to a technology called HCCI being tinkered on at Toyota and GM.

Achates, by the way, was in Roman mythology a close friend of Aeneas, the star of The Iliad.