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To further investigate the flame dynamics inside the special tubes, experiments were carried out in a T-type tube to investigate the effect of the equivalence ratio and the opening ratio on the deflagration of the methane-air premixed mixture. The changes of flame structure, propagation velocity and overpressure during flame propagation are analyzed. The experimental results shown when equivalence ratio was 1.0 and the outlets was fully open, the mixture burned completely, the flame propagation velocity was the highest, it taken only 51 ms for the flame to spread to the exits at both ends and the flame shape was more symmetrical. Under the same equivalence ratio, the increase of the opening ratio would cause the flame propagation velocity to increase, but the overpressure would decrease. When the opening ratio was 0.25, the resistance encountered during the flame propagation process was the largest, and the turbulence at the fork also increased, the interaction between the two caused the maximum overpressure of 0.58 bar at this time. The coupling effect of overpressure and flame front velocity could also clearly show that the two were positively correlated, and the velocity of the flame propagating to the left and right ends of the horizontal tube was symmetrical. When the equivalence ratio was 1.0, as the opening ratio increases, the time to reach the maximum overpressure peak shown a linear downward trend. These findings add to our knowledge of the deflagration dynamics of special tubes. [ABSTRACT FROM AUTHOR]

This study analyzes the effect of both ignition position and hydrogen volume fraction on the flame propagation structure and overpressure wave. The interpretations are based on the propagation dynamics of the premixed syngas/air explosions at different ignition positions with different hydrogen volume fractions investigated at a constant equivalence ratio of 1 in a semi-open rectangular combustion chamber experimentally. The initial temperature T 0 and pressure p 0 were 298 K and 0.1 MPa, respectively. The experimental results are consistent with those obtained using the proposed analytical theory, indicating that the proposed theory predicts the early flame acceleration stage and the flame front motion well under some limited conditions. Flame–wall interaction and combustion instability decrease the theoretical flame front position than the experimental value and increase the wall contact time than the experimental value in some cases. At the same ignition location, both the overpressure growth rate and the maximum overpressure increase with increasing hydrogen volume fraction. When ignited at 0 mm off the closed end, the increased volume fraction of hydrogen would cause the initial location of the tulip flame to approach the opening end of the duct, but at an earlier time. The closer the ignition position to the opening end is, the more intense the overpressure and flame leading edge oscillation are, and the period of overpressure is similar to that of the flame oscillation. Finally, the ignition position and hydrogen volume fraction have obvious effects on overpressure, the structure and development of the flame front. [ABSTRACT FROM AUTHOR]

The effect of laminar flame speed on the flame dynamics in two-dimensional half open tubes is investigated through a two-dimensional laminar combustion model. Several single-step reaction mechanisms are established to alter the corresponding laminar flame speed. The simulation results show that the similarity of flame propagation only holds during the acceleration phase. In the flame acceleration phase, the flame shape and flame tip position corresponding to each dimensionless moment are almost the same. This similarity gradually disappears after the flame touches the wall. When the flame decelerates, the periodic oscillation of the flame tip velocity is related to the laminar flame speed. The higher the laminar flame speed, the longer the corresponding dimensionless oscillation period. The destruction of this similarity is also reflected in the correlation between the flame surface area and the growth rate of burnt gas volume. In addition, the dimensionless evolution correlation of the flame surface area during the acceleration phase is given in this paper. The moving speed of the flame skirt at different laminar flame speeds and the time interval of flame inversion in the two-dimensional half open tubes are also presented. • Simulation of flame dynamics in a two-dimensional tube under different laminar flame speed. • Simplified mechanisms were established to ensure that only laminar flame speeds were changed in the simulation. • The similarity of flame propagation is destroyed after the flame touches the wall. • The relationship between the volume growth rate of the burned gas and the flame surface was found to be different in the four stages. [ABSTRACT FROM AUTHOR]