[Christ]

Glow plugs are used to pre-heat the combustion chamber of the diesel, since diesel engines actually rely on auto-ignition (compression-related ignition, pinging, knocking, etc.) to run... that heat has to be given a starting point... the glow plugs allow the diesel engine to waste less fuel while starting, and start easier than just compressing a bunch of gasses several times to build the heat up.

A potential alternative to the glow plugs is using a fuel that has a high BTU/gallon, but not as high of a octane rating (the word octane is a hint) during startup...

That said - it's dangerous, you probably shouldn't try it, but I've seen it work in controlled situations.

BTW - in case you don't know, detonation resistance of Diesel is measured as "Cetane" ratings... not Octane.