Actually, the miniature .049 glow-plug model airplane engines _are_ diesels, as they don't have any ignition. I seem to recall that in the good ol' days before cars had electric starters, you had to crank the engine to start it. If you weren't aggressive enough, the car would kick back & possibly run backwards for a bit, breaking your arm in the process. Ditto for farm tractors. The problem with jet engines is that they aren't symmetrical: the blades have an orientation. Furthermore, trying to stuff air backwards through the exhaust into the intake won't work, either, because the fuel injectors aren't in the right place. So-called scramjets don't appear to have any moving parts at all, much less rotating parts, so there is no chirality. At 11:45 AM 1/28/2014, Bill Gosper wrote:
What keeps diesels from starting backwards--valving? What about external combustion (jet) engines? An engine with perhaps similar problems can be made from http://toobnix.org/?p=741 http://vimeo.com/38945542 generating compression from increasing the twist (decreasing the pitch) along the length. Further along, the rotors can continuously deform to circularity to accommodate porting.