Not a bad article. It's a little misleading regarding pre-ignition though. While pre-ignition is a form of abnormal combustion, and quite destructive, it is not what causes the phenomenon commonly referred to as engine "knock" or "ping". Pre-ignition does not cause a noise and that is the main reason it is so dangerous. The driver will never know the engine is experiencing pre-ignition until it's too late for the engine. Engine "knock" or "ping" is caused by another form of abnormal combustion known as "Detonation". Although these two abnormal combustion events are commonly confused and often referred to interchangeably, they are quite different. The main difference being that pre-ignition occurs before the spark ignites the combustion charge, and detonation occurs after. Another key difference is that pre-ignition occurs when something inside the combustion chamber gets so hot that it acts like a glow plug and ignites the charge before the sparkplug does, which creates two competing flame fronts in the combustion chamber. This early front does in fact rob power by consuming fuel that should be burned in the normal, spark initiated combustion event but the main problem caused is the extreme pressure and heat it causes. Many people think that these two flame fronts collide and cause engine knock but this is not true. Detonation on the other hand occurs after the spark initiated combustion event. It is caused by spontaneous ignition of end gases left over after the normal combustion event ignites due to the extreme pressure and heat combined with low octane of the fuel. Detonation causes a sharp pressure spike inside the combustion chamber which resonates within the engine causing "knock" or "ping". While detonation can be destructive to an engine, it's generally far less destructive than pre-ignition and thanks to it causing a noise, it can be controlled by the engine control computer through the use of knock sensors and ignition timing adjustments.
This statement still remains in the article: "Anything lower and you risk engine damaging detonation or knocking- the tendency for the fuel to pre-ignite in an engine's combustion chamber." It's a false statement because it describes detonation as a "pre-ignition" event.