Experimental and numerical study on formation mechanism of premixed hydrogen-air squish flame in wall constrained environment

Abstract

The study of hydrogen-air premixed flame propagation behavior and induced accelerated combustion in a constrained environment is of great significance for realizing rapid controllable combustion and promoting the efficient use of hydrogen energy. In this work, the propagation process of hydrogen-air premixed flame and the effect of different initial conditions on flame shape and propagation velocity under the wall constraint were studied in a constant volume bomb using the schlieren method. Then, the flow field characteristics in the wedge space were studied by CFD (computational fluid dynamics) simulation, and the formation mechanism of the squish flame was revealed. The experimental results show that the flame propagation process under wall constraint includes four stages: laminar flame, cell flame, squish flame and spontaneous combustion. The squish flame tends to appear at lower initial temperature in the lean zone and tends to occur at higher initial temperatures in the rich zone. The flame propagation speed increases with the increase of the initial pressure and the initial temperature, but increases first and then decreases with the increase of equivalence ratio. The flame propagation velocity of the rich zone is more sensitive to changes in the initial temperature than the lean zone. The simulation results show that during the flame propagation process, the flow of unburned gas in the wedge-shaped space formed by the flame and the two walls forms a large velocity gradient with the wall surface, which induces strong wall turbulence. The turbulence intensity induced in the wedge-shaped space is higher than that induced by the flame and the single wall surface, and the faster the flame propagation speed, the stronger the wall turbulence generated in the wedge-shaped space. When the flame itself is unstable, the strong wall turbulence in the wedge-shaped space causes the instability or even turbulence of the near-wall flame, which accelerates the rapid propagation of the unstable flame. Therefore, the combination of strong wall turbulence formed in the wedge-shaped space and flame instability results in the formation of squish flame.