I've worked on diesels my whole life..... a few corrections here:

Mr Clayton, glowplugs are often in the combustion chamber. Indirect injection diesels have a seperate combustion chamber with the glowplug and injector in it.

Many diesels can start without glowplugs. It is all dependant on the style of injection, combustion chamber, etc. Many direct injection types will light off just fine with no glowplugs. Many of the engines I work on will have block heaters and other forms of ignition assistance but will often fire off just fine with nothing. (2 stroke detroit diesels are a fine example).

Tool, old VW's, internationals diesels, and many Indirect injection type would eat/destroy glowplugs if the fuel injection timing is way too advanced. The combustion is so instantaneous that it'll shatter/erode the glowplugs.

Drew