Experimental investigation of turbulent flame-shock wave interactions based on abnormal combustion in internal combustion engine

Abnormal combustion phenomena like knock or super-knock are inherent constraint limiting the performance and efficiency of downsized spark ignition (SI) engines.Essentially, engine knock or super-knock is always accompanied by the interactions of turbulent flames and shock waves, as well as rapid chemical energy release.Thus, it is of great significance to investigate the interactions of turbulent flame and shock waves which are the key to reveal the mechanism of knock and super-knock.The major objective of the present work is to experimentally investigate the process of flame acceleration, shock wave formation and interactions of turbulent flame and shock wave in a newly designed constant volume combustion bomb (CVCB) mounted with a perforated plate.In the CVCB, the perforated plate is used to achieve flame acceleration and produce turbulent flame and shock wave.High-speed Schlieren photography was employed to capture the interactions of turbulent flame and shock wave.Hydrogen-air mixture was chosen as the test fuel due to its fast flame propagation velocity and easiness to form obvious shock wave ahead of the flame front.Interactions of turbulent flame and shock wave at different levels could be obtained by changing the initial thermodynamic conditions (including initial pressure and equivalence ratio) and parameters of the perforated plate (including hole size and porosity).Flame acceleration, formation of shock wave and flame-shock wave interactions are discussed in this paper.Depending on the interactions of turbulent flame and shock wave, five combustion modes are obtained by experiments, such as normal combustion, periodically decelerating combustion, oscillating combustion, flame-front autoiginiton and end-gas autoiginiton.The maximum amplitude of the pressure oscillation at combustion models with autoiginiton exceeded 4.5MPa, 4~40 times greater than those without ignition. Therefore, autoiginiton caused by the interactions of turbulent flame and shock wave is the root cause of the intense pressure oscillation in the combustion chamber.