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In spark-ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.
To detect knock, a piezoelectric knock sensor (basically a microphone) bolted to the engine block responds to unique frequencies caused by engine knock. The sensor generates a small voltage that is sent to the electronic control unit , which processes the signal to determine if, in fact, knock is occurring.
Engine knocking (detonation) can be caused by poor quality fuel, an engine fault or if inappropriate fuel and/or ignition settings are trialled/chosen while engine tuning is taking place. If the detonation is severe, the cylinder pressure can increase to eight times above normal pressures, [ citation needed ] which can cause the cylinder head ...
Shocking dashcam footage filmed from a road rage driver's car shows the moment he knocked a motorcyclist off his bike. Graham Robinson, 69, pursued Liam Guest in a 50 mph chase through the Welsh ...
LSPI events are random and infrequent, and their effects on impacted vehicles can include very high-pressure spikes, loud knocking noises and sometimes catastrophic engine damage. [4] It's commonly known as "Detonation or Knock". Engine management systems can overcome pre ignition by the means of a knock or detonation sensor.
Conversely, directly injected engines can run higher boost because heated air will not detonate without a fuel being present. Higher compression ratios can make gasoline (petrol) engines subject to engine knocking (also known as "detonation", "pre-ignition", or "pinging") if lower octane-rated fuel is used. [5]
The reduced engine speeds allow more time for autoignition chemistry to complete thus promoting the possibility of pre-ignition and so called "mega-knock". Under these circumstances, there is still significant debate as to the sources of the pre-ignition event. [3] Pre-ignition and engine knock both sharply increase combustion chamber temperatures.
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