基于发动机非正常燃烧的湍流火焰-冲击波相互作用的实验研究

摘要

Abnormal combustion phenomena like knock or super-knock are inherent constraint limiting the performance and efficiency of downsized spark ignition(SI)engines.Essentially,en-gine 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 investi-gate the interactions of turbulent flame and shock waves which are the key to reveal the mecha-nism of knock and super-knock.The major objective of the present work is to experimentally in-vestigate 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 a-head 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 e-quivalence 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 pa-per.Depending on the interactions of turbulent flame and shock wave,five combustion modes are obtained by experiments,such as normal combustion,periodically decelerating combustion,os-cillating 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 turbu-lent flame and shock wave is the root cause of the intense pressure oscillation in the combustion chamber.%爆震、超级爆震等非正常燃烧现象是限制小型强化点燃式发动机热效率进一步提升的突出瓶颈.爆震或超级爆震发生时总会伴随着湍流火焰-冲击波的相互作用,因此对湍流火焰-冲击波的相互作用的研究是揭示其机理的关键.本文通过在可视化定容燃烧弹内安装孔板实现火焰过孔板加速并产生冲击波,并通过改变初始热力学条件和孔板的参数,来实现不同强度的湍流火焰和冲击波及其相互作用过程.基于该燃烧装置开展了火焰加速、冲击波的形成以及湍流火焰-冲击波相互作用导致不同燃烧模式的研究.根据燃烧室末端火焰传播和压力振荡情况,总结出5种燃烧模式,其中发生自燃的燃烧模式的压力振荡幅值均超过4.5MPa,是未发生自燃时的4~40倍.因此,湍流火焰-冲击波相互作用对燃烧压力振荡具有重要影响.