Compression - The act of compression of any gas produces heat. A diesel produces considerably more compression than a comparable glow engine and that in turn is why a properly designed diesel will have more stoutly constructed upper end.

Also the reason on the first start of the day you must open the compression screw before the first start and adjust. Hitting an overcompressed diesel with a starter will destroy an engine in a flash in exactly the same manner as hitting a hydrolocked glow engine with a starter. Also the reason many diesel flyers prefer hand proping. Once a diesel is properly compressed and needle set will start far easier than any glow engine.

Glow engines actually are considered a semi diesel with a little extra help from a glow plug. That is why you can control the ignition timing of a glow engine with plug heat. A hotter plug will advance the ignition timing BTDC and a colder plug will retard ignition timing.

A hot glow engine if conditions are just right and the state of prime just right subject to many varibles such as engine port design can start accidently with no glow heat attached. Yes I have seen this occur on more than one occasion.

John