Laser-based measurement and numerical simulation of methane-air jet flame suppression with water mist

Abstract

Fire incidents caused by leaks from natural gas pipelines should be quickly controlled by using clean and efficient approaches, such as water mist. Previous studies on the methane-air jet fire suppression by water mist have paid not only little attention to the OH radical distribution characterizing the combustion intensity, but also critical extinguishing conditions of jet fires. Therefore, planar laser-induced fluorescence of the OH radical is obtained to visualize OH radical distribution in fire suppression. Fire Dynamics Simulator v 6.7.4 is applied to simulate the flame-spray interaction and detail the instantaneous fire-extinguishing process by the flow field, gas temperature, reaction methane mass fraction and radiation attenuation in non-lift-off jet flame scenarios. The results show that, considering variation of the jet flame tilt angle, the jet fires can be effectively suppressed when the gas-spray momentum ratio is below 0.0068 in non-tilted cases and normalized Reynold number is less than 2.56 in tilted cases. In the terms of water mist system optimization, the installation location of 1.45 times the pipe diameter was considered as the maximum nozzle horizontal position for fire suppression in the flame Froude number range of 0.2∼1.5. Besides, the OH-PLIF measurement revealed that fire suppression resulting from the kinetics effect depends on whether the OH* flame structure is quickly broken by the downward spray thrust. This study may provide suggestions for natural gas fire suppression with water mist system, and give help for the reduction of greenhouse gas emissions under Paris Agreement.