Assessment of flame height of two unequal turbulent diffusion flames: Experimental interpretation and quantification

Multiple fires burning is a fairly common phenomenon in wildland fires and urban process industries. The burning of multiple fires is much more dangerous than single fire due to the merging of flames. This work aims to study the flame height of two unequal buoyant turbulent diffusion flames, which has not been well revealed. Total 168 experimental tests were performed using two square gas burners with different side lengths of 10 cm and 15 cm as the fire sources. The heat release rates (HRRs) in fire group and burner spacing (S) were changed. Results showed that for a given HRRs group, with the increase of S, the flame height presents a decay trend first, followed by a rise trend, and finally it maintains unchanged. This non-monotonic trend is explained from the view of interaction mechanisms. Three states of fully merging, intermittent merging and non-merging of two flames are divided to illustrate and quantify the flame height. By introducing a normalized parameter lambda to characterize the air entrainment difference, a correlation for flame height of intermittent merging is developed. For the fully merging and non-merging, the equations for flame heights are respectively established based on the assumed equivalent single flame. The accuracy of the proposed model for flame height is validated using experimental data of this work and in literatures. And the application scope of model is expanded to the flame height in merging state of two identical fires.