How a Glow Plug Works?

Spark plugs in gasoline engines start ignition with a spark. In nitro engines, glow plugs cause ignition with heat.

Heat is created initially by connecting a glow starter or 1.5V battery to the plug. Once the plug comes up to heat, the battery is disconnected and the heat retained by the combustion chamber will keep the engine running. Engine timing is automatic and controlled by engine RPM. Running at higher RPM makes the plug hotter and "fire" the fuel-air mix sooner. At lower RPM, the filament cools and the plug fires less frequently.