The diesel engine does not have an ignition system, because due to strong compression, the air is heated so that after fuel is injected into the cylinder, it spontaneously ignites.
Schematic diagram of the Motronic ignition system (models from 1986 release)
1 - ignition lock;
2 - ignition coil;
3 - high voltage distributor;
4 - ignition cables;
5 - tips of candles;
6 - spark plugs;
7 - control device;
8 - battery.
Modern BMW petrol engines are equipped with an electronically controlled ignition system, the control unit of which is integrated into the engine control unit. It does not have a conventional ignition distributor. Instead, the distribution of the high voltage to the individual cylinders is done by fixed electronics. On modern engines, high voltage is generated in six separate ignition coils that are located above the spark plugs. The operation of the ignition system is synchronized by the signals that the pulse generator supplies to the control unit. The pulse generator is located forward on the cylinder block and displays the number of revolutions of the crankshaft.
To determine the right moment (advance angle) The ignition control unit uses an electronic database. Thanks to this, the ignition system easily adapts to various engine operating conditions.
Characteristics of the database of the ignition system
1 - ignition timing;
2 - load;
3 - number of revolutions.
The ignition timing is also corrected by knock sensors. Since fuel consumption at a high compression ratio is minimal, modern engines compress the air-fuel mixture as much as possible. Due to the high compression, however, uncontrolled combustion, called detonation, can occur. Over time, detonation can cause engine damage. To prevent this phenomenon, a knock sensor is needed, which detects uncontrolled combustion and reports this to the control unit, which provides a shift in the ignition timing in the retarded direction. BMW engines have two knock sensors screwed into the cylinder block, one for cylinders no (gasoline with an octane rating of 91), although it will produce less power. When gasoline with an octane rating of 98 is used, engine power is increased.
All parts of the ignition system are matched to each other and always ensure the optimum ignition timing. Ignition timing adjustment is no longer possible.
When working on the electronic ignition system, care must be taken to avoid injury and damage to system components.