An experimental study on burning rates of dual tandem hydrocarbon pool fires of various separation distances subjected to crossflow

Abstract

The intention of this experimental work is to investigate the burning rates of two tandem-placed free-burning square pool fires (15 cm), separated by different separation distances (S/D = 1∼6) under the action of crossflow (0∼6.0 m/s). Two representative hydrocarbon liquid fuels with various sootiness, n-heptane and ethanol, were employed. A total of 204 conditions were considered comprehensively. Results showed that the burning rates of the leading pool fire (LPF) and the following pool fire (FPF) were found to be markedly different from that of the wind-blown single pool fire (SPF) and were attributable to the change of heat feedback mechanisms. The combined effects of the constraint air entrainment and external radiation from the FPF are conducive to the change of the LPF burning rates when tandem pool fires merge. The increment of LPF burning rate compared with SPF burning rate of n-heptane pool fires at a fixed crossflow velocity was deduced to be a function of the external radiation from the FPF when air entrainment is sufficient at a relatively larger separation distance (i.e., non-merging cases). Apart from the external heat transfer to fuel surface and the air entrainment restriction, the sheltering effect of the leading fire on the effective crossflow velocity also dramatically influences the FPF burning rates. The ratio of FPF burning rate to that of a SPF in crossflow, was observed to fall into three phases in terms of a defined Fr⁎ for various separation distances and crossflow velocities, of which phase I with a rising branch, phase II with a falling branch and phase III reached a plateau. Finally, a stagnant film model was employed to correlate well the burning rates of convection-dominated SPF, LPF and FPF under crossflow, while the modified effective crossflow velocity was applied to the FPF. These results provide a basis for better understanding the underlying physics of multiple fires mass burning fluxes caused by complex flame-flow interactions.