Influence of tube cross-section geometry on high-pressure hydrogen-flow-induced self-ignition.

Self-ignition within a cylindrical tube that discharges high-pressure hydrogen results in flame formation. Because rectangular tubes are used to visualize fuel-flow dynamics, the influence of the tube cross-section on the self-ignition characteristics is investigated. As experimental investigation of the mechanisms underlying the self-ignition phenomenon in cylindrical tubes is difficult, three-dimensional numerical simulation is employed. Following the bursting of diaphragm by high-pressure hydrogen with a storage pressure of 9.0 MPa and a temperature of 300 K, initial self-ignition occurs at the center of the rectangular tube sidewall. This is because of the mixing of air and hydrogen induced by the bow-shock reflection-generated jet flow and resulting adiabatic shock compression-induced temperature increase. This temperature rise induces a secondary self-ignition at the tube corners. In the cylindrical tube, a solitary ring-shaped self-ignition occurs near the sidewall. The flame evolutions in rectangular and cylindrical tubes reveal similar flame-spreading trends, which indicates similar bow-shock reflection-induced self-ignition mechanisms. In this study, three-dimensional numerical simulations were performed to evaluate the release of hydrogen at 9.0 MPa through circular and rectangular tubes by the rupture of a diaphragm. The left and right figures show the hydrogen mass fraction and temperature distributions in the cross-section through the axis, respectively. The hydrogen mass fraction distribution indicates the mixing of hydrogen and air near the sidewall of the tube. The temperature distribution indicates the initiation of an exothermic reaction generated by the mixing of heated air and hydrogen induced by the shock wave. [Display omitted] • Examined self-ignition in high-pressure hydrogen jet owing to diaphragm rupture. • Examined the influence of cross-section shape of tube on self-ignition mode. • Self-ignition mechanism near diaphragm is not dependent on cross-section shape. • Flame growth behavior is influenced by the cross-section shape. • The effect of the cross-sectional shape of the tube on self-ignition is insignificant. [ABSTRACT FROM AUTHOR]