Experimental study on the characteristics of flame merging and tilt angle from twin propane burners under cross wind

Multiple fires burning in a windy environment is a special fire phenomenon when multiple flames from separate fuel sources burn simultaneously within a certain space range. It is commonly observed in urban, industrial fires and wildland. To improve the fire safety and achieve optimum energy management, it is important to study the combustion characteristics of multiple fires in wind. This paper investigates the characteristics of flame merging and tilt angle. Twin propane burners aligned parallel to the cross wind with the same energy (heat) release rate were used as energy sources. The experimental results show that with increasing spacing there are three categories of flame merging characteristics, i.e., continuous merging, intermittent merging and non-merging. A new mathematical methodology is introduced to quantify the flame merging possibility in the presence and absence of wind, in counteracting the limitation and uncertainty in traditional method due to the fact of extensive vibration nature of the flames in a wind. Based on the momentum-balance equation, a piecewise function of the flame tilt angles is established in different merging states. Finally, the proposed formulae of flame tilt angles are validated using the literature and experimental data, which show the broad applicability.