Hot tube engine
The hot tube engine is a primitive type of combustion engine, not to be confused with the hot-bulb engine. The timing of a hot tube engine is controlled by means of varying the length of the hot-tube ignitor, that does the job that a spark plug does in a spark ignited engine. Length of the tube controls when the charge ignites, and the ignition timing can be optimized so as to allow different operating speeds to be selected, much like a spark advance control. This engine type is now since long obsolete. It was mostly used as a stationary engine on farms but was also found in very early automobiles and motorcycles.
