For this purpose, a glow plug is installed in each combustion chamber. The glow plug consists of a housing with a heating rod pressed into it. The heating rod in turn consists of a heating coil and an adjustment coil. After voltage is applied, the heating coil in the rod heats up to a temperature of +850°C within a few seconds. The current passing through the plug reaches 30A. As the heating increases, the resistance of the coil increases, which limits the current to 15-25 A. When the pre-glow 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 preheating relay and the engine control unit, which receives information about the current engine temperature via the coolant temperature sensor. The engine control unit, based on the information received, makes a decision on the duration of the glow plugs and the required heating current.
Note: On a direct injection diesel engine, preheating is only required at temperatures below 0°C.