The diesel engine does not have an ignition system, because due to high compression, the air heats up so much that after fuel injection it ignites spontaneously.
BMW petrol engines are equipped with a control card ignition system. The ignition system control is built into the engine control unit. In this case, the ignition is direct. There is no conventional ignition distributor in the system. Instead, the distribution of the ignition voltage to the individual cylinders is carried out through fixed parts that are electronically controlled. A high ignition voltage is induced in six separate coils located above the spark plugs. Synchronization of the system operation is carried out using pulse sensor signals transmitted to the control unit. The pulse sensor is located in front of the cylinder block and registers the crankshaft speed.
The determination of the required ignition timing is carried out by the control unit based on the characteristics stored in the memory (management cards). Thanks to this, the ignition system easily adapts to various operating conditions.
The ignition timing is influenced by the knock sensor signal. Since the best fuel consumption occurs at a high compression ratio, it is assigned as high as possible in modern engines. However, a high compression ratio can lead to uncontrolled combustion, in which case one speaks of knocking combustion in the engine. Prolonged knocking can damage the engine. To avoid this, a knock sensor is required, which registers a violation of combustion and transmits a signal to the control unit, which makes sure that the ignition is delayed. BMW vehicles have 2 knock sensors located on the engine block. One sensor controls the combustion process in cylinders 1-2-3, and the other - in cylinders 4-5-6. Thanks to the regulating action of the knock sensors, the engine can be operated on gasoline with a lower octane number (Normal 91), however, a reduction in engine power is inevitable.
All components of the ignition system are coordinated, so that the optimum ignition timing is always guaranteed. Ignition timing adjustment is no longer required.
To avoid personal injury and damage to the ignition system, when working on the electronic ignition system, the safety regulations must be observed.