Editing Octane rating (section)

===The problem: detonation===
{{Main|Engine knocking}}
In [[spark ignition]] [[internal combustion engine]]s, '''knocking''' (also '''knock''', '''detonation''', '''spark knock''', '''pinging''', or '''pinking''') occurs when combustion of some of the [[air-fuel ratio|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. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the [[four-stroke cycle]]. In a simple explanation, the forward moving wave of combustion that burns the hydrocarbon + oxygen mixture inside the cylinder like a wave that a surfer would wish to surf upon is violently disrupted by a secondary wave that has started elsewhere. The shock wave of these two separate waves creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential (incremental heating plus power loss) to completely destructive (detonation while one of the valves is still open).

Knocking should not be confused with [[pre-ignition]]{{snd}}they are two separate events with pre-ignition occurring before the combustion event. However, pre-ignition is highly correlated with knock because knock will cause rapid heat increase within the cylinder eventually leading to destructive pre-detonation. <ref>{{Cite journal |last1=Wang |first1=Zhi |last2=Liu |first2=Hui |last3=Song |first3=Tao |last4=Qi |first4=Yunliang |last5=He |first5=Xin |last6=Shuai |first6=Shijin |last7=Wang |first7=JianXin |date=February 2015 |title=Relationship between super-knock and pre-ignition |url=https://journals.sagepub.com/doi/10.1177/1468087414530388 |journal=International Journal of Engine Research |language=en |volume=16 |issue=2 |pages=166–180 |doi=10.1177/1468087414530388 |issn=1468-0874}}</ref>

Most [[engine management system]]s commonly found in automobiles today, typically [[Fuel injection|electronic fuel injection]] (EFI), have a [[knock sensor]] that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the [[ignition timing]] will be automatically altered by the engine management system to reduce the knock to an acceptable level.