I guess; when unburned fuel and air mixture beyond whats required remains under heat and pressure; causes detonation...famously Knocking!
From Wikipedia; Detonation can be prevented by any or all of the following techniques:
- the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate;
- enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder;
- reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear, there is also evidence that knock occurs more easily at low rpm than high regardless of other factors);
- increasing mixture turbulence or swirl by increasing engine revolutions or by increasing "squish" turbulence from the combustion chamber design;
- decreasing the manifold pressure by reducing the throttle opening; or
- reducing the load on the engine.
These new engines are sensitive...each engine has different required RON (Octane); using fuel from good pumps ensures that fuel has all the RONs.
