Is multitasking a good thing? It often is, but not in the form of detonation, or spark knock. Normally, fuel burns smoothly in the combustion chambers as one flame front that expands outwards from the ignition point. Detonation refers to erratic combustion that occurs when multiple flame fronts form on their own throughout the chamber; as the flame fronts collide, we hear knocking or metallic pinging. The sound is most evident when you ask the engine to work harder, such as accelerating with a heavy load.