Diesel engine preheating system (BMW 7 Series E32)

On a cold engine, the autoignition temperature is not reached by air compression alone, so the engine needs to be warmed up.

For this purpose, a pin glow plug is screwed into each combustion chamber. The glow plug consists mainly of a housing with a heated rod pressed into it. When voltage is applied to the plug, the heating winding in the rod heats the rod to a temperature of more than 850°C, due to which the pre-start glow period rarely lasts more than 5 seconds. When the pre-heating indicator lamp goes out, the engine can be started. Pre-heating period, as well as automatic glow after starting (up to 20 seconds) controlled by the DDE control unit via a pre-heating relay.

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