The last available news on the Gemini appears to be from around late 2009. There's no substantial developments to report. Tim Archer talks up the Gemini at a 2009 expo in the video below... but the bottom line is...
1. The Gemini isn't radical enough to be able to claim a serious advancement in engine technology, weight saving, and fuel efficiency.
2. Just fiddling with a WW2 Junkers Jumo design, only produces the same problems that saw the Jumo development abandoned.
There's no way of building a substantially lighter weight, water-cooled, highly fuel efficient diesel, using the opposed piston design.
The last news was that Power Plant Developments were doing "fuel mapping" in late 2009. I would suspect that this engine is going nowhere.
The company is probably at the stage of looking for more money... as many of these "new engine" companies burn up money faster than they can get people to invest.
Thus we have most of these so-called "revolutionary" aircraft diesels, all stalled at the point of progress, of about 5-6 years ago.
Some have fallen by the wayside, most are stalled on age-old problems of keeping weight down... reliability at a high level... sealing... cost at satisfactory levels... and a failure to offer SUBSTANTIAL advances in technology.
Even the so-called, fabulous Rand-Cam engine has stalled... on the age-old problem with all rotary-style engines, of massive problems with sealing.
The Rand Cam engine has now morphed into the RadMax, after the Rand Cam engine failed to live up to all its claims.. but the RadMax engine is still not a runner, either.
These perpetual sealing problems were the downfall of the Sarich Orbital engine... it was a major problem with the Wankel engines... and it haunts every rotary engine developer.
The Raptor Turbo diesel has nothing to offer over anything else available. A convential 4 cyl engine placed horizontally, is only inventing the wheel again.. but with a different hubcap, to try and convince people it's a radical development.
Gemini Diesel interview - Tim Archer ..
Gemini Diesel 100 HP aircraft engine, PPD Gemini aircraft engine manufacturer, Lightsport Aircraft Pilot Video newsmagazine.
Raptor Turbo diesel ..
Raptor Turbo Diesel
RadMax engine ..
RadMax Technologies, Inc.