Yes, there were straight Diesel model airplane engines- - - -they had a thumbscrew built into the cylinder head to increase the compression. It usually took a battery powered prop spinner to crank one fast enough to light off the fuel. Finger-flipping one usually caused a kickback and a cut finger. LOTS more power (and noise) than a glow plug engine! Operating RPM was in the 20-25K range.

There's about 100 of them on Ebay today. Search "Diesel model airplane engine".
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!