Effects of cross airflow and burner distance on temperature profile and flame morphology of dual tandem pool fires

Understanding multiple fire sources interactions in cross airflow that frequently occur in wildland fire or industrial process accident scenario is helpful for establishing guidelines for fire protection engineering. This paper experimentally studies the thermal characteristic and flame behavior of dual tandem pool fires with equal-and unequal-heat release rates in varying separation distances (S) under cross airflow (u). Two square diffusion burners were used employing propane as fuel with varied heat release rates (HRR) at six separation distances, with a total of 216 experimental conditions were considered comprehensively. Flame merging condition, IRmeasured flame temperature profile, flame height and flame horizontal projection length were quantified and analyzed. Results show that the flames tend to merge more easily in cross airflow when the HRR of the upstream flame is larger. The maximum temperature in the flame region increases with the increasing cross airflow velocity for both merging and non-merging flames, and the downstream pool fire's maximum temperature is lower than that of the upstream pool fire in the cases of non-merging. For merging cases, flame horizontal projection length decreases as S/D increases, while flame height changes little for varying S. For non-merging cases, flame height of downstream pool fire has an increasing trend with the increasing separation distance, while flame horizontal projection length declines in reverse due to the flame blockage effect. Three combustion states of dual fires are identified according to their force interactions: State I-pressure thrust dominated, State II-pressure thrust competes with cross airflow inertial force, State III-cross airflow inertial force dominated. Finally, a scaling analysis is performed to characterize the flame height and horizontal flame projection length based upon the competition mechanisms between total buoyant flow flux and cross airflow momentum flux for merging flame and non-merging flame in state III. This study provides experimental data and a scaling analysis into the fundamental physics of equal and unequal multiple pool fires interactions under cross airflow.