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Knock Sensor

The knock sensor is fitted to the outside of the engine and prevents damaging spontaneous ignition.
The knocking effect is created by acyclic uncontrolled combustion, which produces extreme local temperatures in the cylinder. These high heat quantities place a severe strain on engine components such as the pistons, valves and cylinder head, and can lead to damage.
The knock sensor registers the structure-borne noise emissions of the engine.
The engine control unit cross-checks the measured pulses against the stored specification values and intervenes to control the engine, fuel injection and ignition as necessary, before the combustion reaches the knock limit.
The knock sensor also detects the fuel quality. The higher the octane number (RON), the more knock-proof is the fuel. This means 98 RON Super Plus grade fuel ignites at a higher temperature than normal 95 RON petrol. If only a lower quality of fuel is available, the engine control unit automatically corrects the ignition timing based on the information from the knock sensor. This prevents damage to the engine.