As the plug continues to heat up, it opens a valve permitting diesel from a special reservoir mounted directly above the Thermostart into the Thermostart plug. This fresh diesel is also vaporised and adds to that in the inlet manifold. At 20 seconds, provided air is available, the diesel near the plug ignites and as the engine is cranked, the ignited diesel is drawn into the combustion chambers - to which more diesel is added after the compression stroke.