Experimental study on the characteristic stages of premixed hydrogen-air flame propagation in a horizontal rectangular closed duct

Deep insight into each stage of premixed hydrogen-air flame propagation in a horizontal rectangular closed duct was experimentally realized with pressure records and high-speed schlieren photographs under various equivalence ratios. The motion patterns of the flame skirt and the contact point sweeping along the wall were divided into multi-section with distinct features. Two types of tulip cusp motions were scrutinized and distinguished within different equivalence ratio ranges. The vibrations of the flame tip position and velocity were determined as common features in the whole observed range of equivalence ratios. But the tulip distortion is conditional and substantially originates from the vibration just with more remarkable amplitude. The change of pressure difference between the measure points respectively close to the left and right ends of the duct correlates well with the flame tip velocity oscillation with a 90° phase prior. The experimental results were compared with the theoretical prediction. Best agreements are only achieved in a narrow range of equivalence ratio ∅=0.91∼2.24$\varnothing =0.91\sim 2.24$, which reveals some limitations of the theoretical model by Bychkov et al.