How does Auto Octane (adjustable octane, OAR, Octane Ratio,etc.) and Knock sensors determine octane?

Higher octane fuel is better for turbocharged engines because it's more resistant to

engine knock, which can improve performance and prevent damage.

Your vehicle doesn't actually have the ability to recognize the octane level of the fuel in

its tank. Instead, the engine controller uses a closed-loop system to estimate the octane

rating by continuously adjusting the ignition timing until it detects knocking. Knocking

happens when part of the fuel-air mixture ignites before the flame front from the spark

plug reaches it. The more the computer can advance the timing without causing knock,

the higher the inferred octane rating. When knocking occurs, the flame front can move

through the combustion chamber up to ten times faster than the usual spark-initiated

flame front. If left unchecked, these pressure waves could potentially harm the head

gasket, pistons, or cylinder head. However, a brief instance of knock can actually be

beneficial for ensuring the engine runs efficiently. This is monitored by one or more

knock sensors attached to the engine block, which detect the oscillations caused by the

pressure waves, typically within a frequency range of 7 to 16 kilohertz. According to

Stephen Russ, a senior technical leader for gas engines at Ford, this normal knocking is

usually identified and corrected within one or two combustion cycles, and it doesn't pose

any risk to the engine.  However, having a calibration for a specific octane fuel is always

the best way to keep your engine safe.