You might want to check out the NASA website as well. As part of their GAP (General Avaition Propulsion) project, they have teamed up with Teledyne-Continental to develop a diesel 4-cyl powerplant with a compression ratio of 18:1, which eliminated the need for a spark/glow-plug i.e. ignition system, is very efficient, and burns Jet A or A+. It is also liquid cooled, lightweight, 25% more efficient fuel burn, and costs 50% less to manufacture than the air-cooled normally aspirated Continentals. It will also be turbocharged and will not need a mixture control. Hopefully it will be certified soon. NASA is also working with Williams on a small turbofan for use in 6-10 person jets that will be cheaper to own & operate than an equivalent piston or turboprop. Check it out (sorry I don't have the URL, just go to the NASA mainpage & follow the links).