The effect of open-end ignition at different positions on the explosion behaviors of H2/CO/Air in variable cross-section pipe.

This work is focused on the explosion performance of syngas/air premixed gas in a self-designed variable cross-section pipe under varying ignition positions (IP 1 , IP 2) and hydrogen volume fraction (α(H 2)). Results show that α(H 2) has a great influence on the propagation of the flame as well as the maximum flame front velocity (FFV max) and the maximum overpressure (P max). As α(H 2) in the syngas increases, the time the flame stays in the pipe is gradually reduced, the FFV max as well as the P max increase regardless of the ignition position. Differently, when α(H 2) < 50%, the t closed at IP 1 is shorter than that at IP 2. The opposite is true when α(H 2) ≥ 50%. This is attributed to the difference in flame velocity and the effect of film breakage. Both α(H 2) and variable cross-section chamber structure all affect the evolution of the flame morphology. When ignition at IP 2 , a "M" flame is observed for the first time at α(H 2) = 20%, and a flame resembling a "T" shape appears at α(H 2) = 70%. Ignition positions have a great influence on overpressure oscillation. In the case of α(H 2) = 15%, the Fourier transform is performed for the pressure curve. When ignited at IP 1 , secondary unstable oscillations occur during the later stage of flame propagation. However, when ignition at IP 2 , primary instability oscillations occur in both the early and late stages of flame propagation. The variable cross-section chamber structure plays a role in the flame front velocity (FFV) and overpressure. After the flame front enters the variable section chamber, the FFV reduces, and when the flame front leaves the variable section chamber, due to the sudden decrease of the cross-sectional area, the FFV increases significantly, and FFV max and P max are obtained at this moment. • A self-designed variable cross-section pipe is studied. • Open-end ignitions at varying positions are analyzed. • When ignition at IP 2 , a "M" flame is observed for the first time at α(H 2) = 20%. • Pressure oscillation frequency is different under different ignition positions. • When the flame front leaves the variable section, FFV max and P max will be obtained. [ABSTRACT FROM AUTHOR]