For this purpose, a glow plug is installed in each combustion chamber. The glow plug consists of a body with a heating rod pressed into it. The heating rod, in turn, consists of a heating coil and a control coil. After applying voltage, the heating coil in the rod heats up within a few seconds to a temperature of + 850°C. In this case, the current passing through the candle reaches 30A. As the heating increases, the resistance of the coil increases, which limits the current to 15 - 25 A. When the preheat indicator lamp on the instrument panel goes out, the engine can be started.
The preheating time required to start the engine is no more than 10 s. The time is regulated by the preheat relay and the engine control unit, which receives information about the current engine temperature through the coolant temperature sensor. Based on the information received, the engine control unit decides on the duration of the glow plugs and the required heating current.
Note. On a diesel engine with direct injection, preheating is required only at temperatures below 0°C.