OK, The system is Pre-glow plugs and works quite well for cold starts in Winter.
There are two types of thermal-start. One automatically fills from the return line back to the tank and drips diesel fuel on the small igniter located at the intake manifold. It does this when the key is turned fully left, powering up the igniter and pre-burning the fuel prior to cold start.
The other type you have to physically fill the bottle and the rest works the same. Hope this helps.
Mark