Free piston engines could achieve efficiencies of 50% which is almost double a regular gas combustion engine. However, new super efficient diesel engines could be even better, plus diesels would be more familiar to the market place.
Some small companies are working on free piston engines and there are researchers around the world at Sandia and other places working on them.
There was a discussion at greencarcongress about free piston engines versus the most efficient new diesel engines.
The 14th Diesel Engine-Efficiency and Emissions Research (DEER) Conference was held on August 4-7, 2008, at the Hyatt Regency Dearborn in Dearborn, Michigan discussed the latest research in high efficiency technology for cars.
Vinod Khosla, active venture capitalist investing in green and clean technology, has invested in Ecomotors.
Ecomotors has a two-cylinder diesel engine that's lighter, more powerful, and easier to scale up than today's engines, says Ford Tamer, operating partner at Khosla Ventures. The design could wind up boosting a diesel engine's efficiency—which is already 20% to 40% better than those of gas engines—by half. [Note: this could be as high as 57% efficiency] The two-cylinder units can be clicked together like Legos: by linking them in a series, designers can build the sorts of larger engines with four, six, or eight cylinders that are typically used in cars and trucks.
Details on the patented design are still hush-hush, but the design uses horizontally opposed pistons, like those in Subaru's gas-powered "boxer" engine. Because the pistons are always moving in opposite directions to one another, they cancel out most of the stress they'd otherwise transfer into the engine block. This allows the design to be lighter than conventional engines, where the pistons are inline or in a V configuration. EcoMotor's approach cranks out about 1 hp per pound of engine weight, says Tamer, 20% better than the highly tuned engine on a Porsche 911, and 300% better than many mass-market engine designs.
Notice that the opposing piston looks similar to the free piston engine configuration, but does not have a solid shaft between the two chambers.
Ecomotors is hoping to develop a four-door sedan by 2010 that gets 100 miles per gallon.
EcoMotors International Inc. currently employs seven people, occupying a building in the 2400 block of West Big Beaver, according to city Assessor Nino Licari. The company plans to purchase $3.5 million in new equipment and move into a 30,120-square-foot facility at 1055 W. Square Lake, Licari said. EcoMotors plans to hire 150 new employees in the first two years, according to Licari. They are applying for local tax breaks.
Diesel Engines at wikipedia
Homogeneous Charge Compression Ignition (HCCIP) engines. Up to 15% more efficient than regular engines, while meeting current emissions standards.
BMW advanced diesels are better than some hybrid cars in terms of fuel economy
BMW plans on increasing efficiency by another 15%
Research presentation from the 14th Diesel Engine-Efficiency and Emissions Research (DEER) Conference.
Identification and evaluation of near-term opportunities for efficiency improvement. by Dean Edwards of Oak Ridge National Labs
Brief two slide poster about free piston engine.