Abstract: An after glow control system for an engine, which controlls the voltage to be applied to glow plugs of the engine, is disclosed. The system comprises a first electric path through which a voltage is applied from a battery to glow plugs during the preheating period and a second electric path which is connected to the first electric path in parallel and through which a voltage is applied from the battery to the glow plugs during the after glow period. In the second electric path, a voltage dropping circuit of a switching type is provided. The voltage dropping circuit is provided with a switching means between the battery and the glow plugs and a switching control circuit which controls the opening and closing period of the switching means.

Abstract: A ceramic heating element is held in a metal housing to be mounted on an internal combustion engine, so that the heating element is operated as a glow plug for igniting an air-fuel mixture. The ceramic heating element is formed of an electrode section housed in the housing and a heat generating section extending out of the housing, whereby the heat generating section is exposed to the mixture in an engine cylinder. The electrode and heat generating sections are divided into two portions, respectively, and both forward ends of divided heat generating portions are connected with each other, so that electric current flows from one of the electrode portions through the divided heat generating portions to the other electrode portion.

Abstract: A glow plug for rotary piston engines adapted to be mounted in an engine plug hole so as not to project from the plug hole and to be traversed by a flow of fuel-air mixture temporarily trapped in the plug hole. The plug includes an elongated protective tube providing a straight root portion by which it is supported from a plug housing adapted to be inserted in a plug hole. The tube terminates in a closed end hook-shaped free tip portion spaced from the root portion and plug housing and lying in the same plane as the root portion. A helical heater coil is disposed in the protective tube with the pitch of the coil being smaller at the free tip portion than at the root portion so that greater heat is generated in the free tip portion than in the root portion.