Propagation characteristics of turbulent deflagration in horizontal tunnel with lateral liquefied petroleum gas concentration variations

Abstract

The deflagration of premixed gas with a non-uniform spatial distribution is one of the critical characteristics observed in deflagration accidents in tunnels. The concentration gradient of premixed gas in the propagation direction of the deflagration flame in the tunnel is an important factor influencing the propagation of deflagration. In this study, the numerical simulation of the deflagration process in two adjacent areas with different initial concentrations of premixed liquefied petroleum gas (LPG) was implemented in a tunnel with a unidirectional opening. The dynamic coupling characteristics of the lateral concentration difference of the premixed gas in the tunnel, the deflagration propagation process, and the concentration gradient mechanism that promotes or inhibits the initial deflagration propagation were analysed. Staged violent deflagration can be induced by a sharp transition from weak initial deflagration under an appropriate concentration gradient to unforeseen severe deflagration overpressure destruction and flame propagation. In a tunnel with a large cross-sectional area, the difference in the concentration of premixed gas along the propagation path of the deflagration flame can also cause the local protrusion of this front, thereby increasing the spreading ability of deflagration flame at the local location. However, an excessively high concentration gradient may hinder the initial propagation of deflagration to a certain extent, limiting the expansion space of combustion heat and reducing the propagation speed of a flattened deflagration flame front. To characterise the propagation velocity of deflagration flame in the tunnel formed by two zones with different initial premixed LPG concentrations, a dual-zone model that combines power and exponential functions was proposed. The validity of the model was also verified.