Experimental study on the deformation and oscillation of premixed syngas/air flames in closed ducts

Abstract

Experiments were conducted in two closed ducts, 100 × 100 × 1000 mm3 (AR = 10) and 60 × 60 × 2000 mm3 (AR = 33.33), to comparatively study the explosion behavior of premixed syngas-air mixtures. The stoichiometric syngas-air mixtures with the increase in hydrogen volume fraction were tested. The flame structure, flame tip, and overpressure dynamics in two ducts were analyzed, and the propagation behavior was compared according to the two flame types through the flame structure and flame tip dynamics. Results show that the development of the flame’s structure is predictable in AR = 10, but the development of the flame’s structure is complicated in AR = 33.33. Increasing both the hydrogen volume fraction and the aspect ratio of the duct increases the amplitude of the flame oscillation, and the flame in AR = 33.33 shows a stronger deformation and oscillation. There is a strong correlation between flame tip speed and overpressure profiles. The growth rates of Darrieus-Landau (DL) and Rayleigh-Taylor (RT) instabilities were presented and discussed, and the results show that both DL and RT instabilities significantly affect flame propagation behavior. Finally, the flame exhibits different structural changes, but it is confirmed that the response sources of the flame oscillation in the two ducts are the same, i.e., owing to the pressure wave’s excitation.