Effect of air entrainment on the height of buoyant turbulent diffusion flames for two fires in open space

This paper presents a quantitative analysis and interpretation on the effect of air entrainment on the height of buoyant turbulent diffusion flames for multiple fires in open space. Two identical gas burners with the same heat release rate (HRR) were used as fire sources. Experimental results show that the flames would merge at fire spacings less than 0.3 times the flame height without spacing. Merging flames are confirmed when the flame merging probability is no less than 0.5. A parameter, lambda, is introduced to determine the flame height with a segmented function, where (1+lambda) is defined as the ratio of air entrainment rates in cases with respective no spacing and spacing. Analysis shows that when the normalized HRR does not exceed 3.58, the flame height is barely affected by the fire spacing. When the normalized HRR is greater than 3.58, for merging flames, lambda can be considered as a constant with average value of 0.07 and the normalized flame height is relevant to the temperature rise in the additional region. While for non-merging flames, the normalized flame height is related to lambda, which is proportional to 2/5 power of the normalized HRR. Finally, the proposed equations in this work are validated using literature data, which presents high reliability. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.