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High boost and direct injection hold the potential of enhanced power density and fuel consumption in the development of gasoline engines. However, super-knock with strong destructiveness was widely reported at low-speed and high-load operating regime in turbocharged GDI engines. The objective of this study is to clarify the characteristics of super-knock and to try to find some feasible solutions to suppress super-knock. To fast evaluate super-knock at low-speed and high-load regime, a rapid test procedure including three super-knock test sections of 5000 cycles with 3 idle operations, was proposed. The experimental data indicate that pre-ignition is not the sufficient condition for super-knock. Pre-ignition may lead to super-knock, heavy knock, slight knock, and non-knock. Compared with conventional knock, knock intensity of super-knock is much higher and the maximum amplitude of pressure rise at start of knock is more than one order of magnitude higher.

A 1-Dimensional (1-D) model of fluid dynamic and chemistry kinetics following hot spot auto-ignition has been developed to simulate the process from auto-ignition to pressure wave propagation. The role of wall effect on the physical-chemical interaction process is numerically studied. A pressure wave is generated after hot spot auto-ignition and gradually damped as it propagates. The reflection of the wall forms a reflected pressure wave with twice the amplitude of the incident wave near the wall. The superposition of the reflected and forward pressure waves reinforces the intensity of the initial pressure wave. Wall effect is determined by the distance between the hot spot center and the cylinder wall. Hot spot auto-ignition near the wall easily initiates detonation under high-temperature and high-pressure conditions because pressure wave reflection couples with chemical reactions and propagates in the mixture with high reactivity.