Numerical study on merging and interaction of jet diffusion flames

A high velocity jet fire can cause catastrophic failure due to flame impingement or radiation. The scenario becomes more complicated when multiple jet fires exist following ignition of release from pressure relief valves (PRV) as the thermal effect not only distorts the individual jet flame but also changes the flame height and temperature profile and such kind of high velocity jet flames have not been studied in the past. Therefore, prediction of the flame shape including the merging and interaction of multiple jet fires is essential in risk analysis. In this paper, fire interaction of two high velocity (>10 m/s) jet fires is investigated using computational fluid dynamics (CFD) techniques. Different radiation models are analyzed and validated by experimental data from the literature. Based on the simulation result, the merging of high velocity jet fires is divided into three stages. An empirical equation considering the fire interaction for the average flame height with different release velocities and separation distance is developed. The flame height increases dramatically when the separation distance decreases resulting in a shortage of oxygen. So, part of the methane is reacted in a higher height, which explains the change in the merging flame height and temperature.