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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]

This paper explains the basic knowledge to understand the relationship between overpressure wave behavior and the structure of flame propagation, especially the effects of the ignition position and opening ratio on the combustion dynamics. The explanations are based essentially on the experimental investigations of premixed syngas/air explosions carried out at a constant equivalence ratio of 1 and the hydrogen volume fraction of 0.3 in a rectangular half-open combustion chamber. The initial temperature T 0 and pressure p 0 were 298 K and 0.1 MPa, respectively. The four ignition positions were set at 0, 150, 450 and 750 mm off the left of the combustion chamber. Four different opening ratios of the duct were employed, including 0.25, 0.5, 0.75, and 1. The obtained results show that ignited at IP 0 , the increased opening ratio would cause the distorted tulip flame to disappear, accompanied by the propagation direction change of flame front. At the same ignition position, when the opening ratio increased, the oscillation amplitude of overpressure, and the velocities of the right-hand and left-hand flame all rose, but the overpressure growth rate and maximum overpressure decreased. As the ignition position approached the opening end, the overpressure and the flame front oscillations became more intense. It is indicated that different ignition positions and opening ratios exerted obvious effect on the flame front propagation and the overpressure. [ABSTRACT FROM AUTHOR]