Knocking was studied on a boosted single cylinder optical gasoline engine. The auto ignition and extreme-knock development processes have been captured in a wider view with the adjustment of engine operating parameters and high-speed imaging technology. The combination of the recorded images and in-cylinder pressure data has provided the information for understanding the origins of the auto-ignition and the huge pressure oscillation magnitude of super-knock. The results show that the pressure oscillation and flame image of the light knock caused by the auto-ignition of unburned end gas are remarkably different from those of the extreme-knock caused by pre-ignition. The development modes of auto-ignition play an important role in the in-cylinder pressure oscillation magnitude

causing auto ignition kernels to get close to but in direct contact with the cylinder walls

therefore surface ignition can be ruled out. Auto-ignition kernels can generate flame propagation

which is restricted by the main flame and cylinder walls.