For you gear heads that are interested in engine designs in general, this is interesting. So interesting, that the DOD handed Cummins $48 million to start putting them in military applications.
You may remember that Junkers 205 2 cycle opposed piston diesel engines went into large aircraft - bombers and cargo and passenger planes around WWII time frame.
Well the design is getting a new look with modern computer control technology. They claim it is more fuel efficient and has lower emissions than current engine designs.
Opposed-Piston - Achates
The power to weight ratio of typical diesel engines keep them out of air craft, but this design has a better power to weight ratio than many gasoline engines.