Bill Brogden seems to think this is the most promising of the aerodiesels.
http://bmepinc.com/AEHS%20presentati...%2005%2008.pdf
There was a flurry of press releases a couple of years ago about Lycomings iE2 series but it seems to have gone quiet lately.
http://www.lycoming.com/news-and-eve...iE2_Engine.pdf