Egon, There are at least three distinct types of ICE used for (small) model airplane engines, the type that make your chainsaw jealous. The glow engine uses a glo plug which enables starting the engine with fuel that used to be castor oil, alcohol, and nitromethane but can be lots of synthetics stuff these days. The glow plug retains enough heat between firings in its exposed coil of heater wire to help ignite each succeeding dose of fuel and air. The compression is way lower than a model airplane diesel.
There are model airplane diesel engines and the ones I have struggled with do not have glow plugs and are true compression ignition. The ones I have seen have a compression adjustment which is essentially a screw you turn to move a piece of metal into or out of the combustion chamber to take up more or less space. The fuel used is not at all like automotive diesel. When I was around these engines the fuel had a high ether content. They aren't the easiest starting engines, especially in winter.
There are also true spark ignition engines in truly small sizes used on model airplanes. Some of these predate a lot of the glow plug engines and were used before my time (yes, while the big rocks were still hot.) Imagine a model airplane with a 8-10 inch propeller spun by an engine with an itsy bitsy standard spark plug. The displacement would have been in the range of about 0.25 to 0.45 cubic inches and the plane would have had to carry batteries to power the points-plug-condenser-ignition coil type arrangement. Never having had or actually operated one of those engines I can't speak from memory about the fuel. I did buy one of the planes that had originally had a spark ignition engine but the engine was missing and I substituted a Testors brand 0.35 cubic inch glow engine after completing flight testing with a 0.01 cubic inch glow engine which turned over 20,000 RPM with about a 3 inch prop (Cox Thimble Drome line.)
Larger flying models sometimes use chain saw motors or even small jet turbines.
Navy "Heavy Fuel" requirements (the Navy doesn't like to use gasoline or other dangerously volatile and explosive fuel on board a super carrier) has spurred the development of diesel engines for use for shipboard based UAV (Unmanned Aerial Vehicles.) There is precedent for diesel powered aircraft. Manned diesel aircraft were tried way back when and in the mid 20th century the Germans and Japanese both did extensive diesel aircraft trials.
Do a Google on diesel aircraft or similar and you'll see that diesel aircraft engines, although not mainstream, are not hard to find.
...oh, by the way... weren't the early injected 'Vettes, direct injection into the combustion chamber, like way before the "modern" "external" injection? I'm not positive as I have never been a big fan of Corvettes and didn't track them closely.
Pat
