Glow Plugs

With a glow plug engine, ignition is initiated by the application of a 1.5-volt power source. When the battery is disconnected, the heat retained within the engine's combustion chamber remains sufficient to keep the engine running. Ignition timing is 'automatic': At higher rpm, the plug becomes hitter and, appropriately, fires the fuel/air charge earlier; at reduced rpm, the filament becomes cooler and ignition is retarded.