Quote:
Originally Posted by MerF
The cylinders won't even feel the effects of pinging. The damage is done on the head, piston, and rotating assembly. Of course, when any of these three fail, the effects will be that something goes sideways instead of up and down, and THAT'S when the cylinders get hosed.
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well I was trying to keep it short...but MerF I do totally disagree with you on what I got quoted. detonation even on a naturally aspirated vehicle wears down the cylinder wall. I had to pull out the TECH MANUAL on ya!
The fuel/air mixture is normally ignited slightly before the point of maximum compression to allow a small time for the flame-front of the burning fuel to expand throughout the mixture so that maximum pressure occurs at the optimum point. The flame-front moves at roughly 33.5 m/second (110 feet/second) during normal combustion. It is only when the remaining unburned mixture is heated and pressurized by the advancing flame front for a certain length of time that the detonation occurs. It is caused by an instantaneous ignition of the remaining fuel/air mixture in the form of an explosion. The cylinder pressure rises dramatically beyond its design limits and if allowed to persist detonation will damage or destroy engine parts.
A non conventional engine that makes use of detonation to improve efficiency and decrease pollutants is the Bourke engine.
Detonation can be prevented by:
The use of a fuel with higher octane rating
The addition of octane-increasing "lead", methylcyclopentadienyl manganese tricarbonyl (MMT), isooctane, or other antiknock agents.
Increasing the amount of fuel injected/inducted (resulting in lower Air to Fuel Ratio)
Reduction of cylinder pressure by increasing the engine revolutions (lower gear), decreasing the manifold pressure (throttle opening) or reducing the load on the engine, or any combination.
Reduction of charge (in-cylinder) temperatures (such as through cooling, water injection or compression ratio reduction).
Retardation of spark plug ignition.
Improved combustion chamber design that concentrates mixture near the spark plug and generates high turbulence to promote fast even burning.
Use of a spark plug of colder heat range in cases where the spark plug insulator has become a source of pre-ignition leading to detonation.
Correct ignition timing is essential for optimum engine performance and fuel efficiency. Modern automotive and small-boat engines have sensors that can detect knock and retard (delay) the ignition (spark plug firing) to prevent it, allowing engines to safely use petrol of below-design octane rating, with the consequence of reduced power and efficiency.
A knock sensor consists of a small piezoelectric microphone, on the engine block, connected to the engine's ECU. Spectral analysis is used to detect the trademark frequency produced by detonation at various RPM. When detonation is detected the ignition timing is retarded, reducing the knocking and protecting the engine. See also Automatic Performance Control (APC).
Consequences of Knocking
Engine knocking has disastrous consequences for the engine, since it leads to the catastrophical wear of the combustion chamber walls, through particle wear for moderate knocking, to welding for serious knocking. This is due to the contact between those walls and high temperature gases resulting from the unwanted explosion. The processes also lead to a 'knocking' noise for the engine, that give its name to the phenomenon.