Transitional behavior of vertical flame height of horizontally-oriented rectangular-source jet fires

This work studied the projected vertical flame height of buoyant turbulent horizontally-oriented rectangular-source jet fires. Nine burners with three exit areas and various aspect ratios (1-1 to 71-1) which including axisymmetric, rectangular and line-type sources were used in the experiments. During the exper-iments, the shorter side of the burner was perpendicular to the ground. The projected vertical flame height Hf, refers to distance between the burner and the flame tip in the vertical direction, was measured and ana-lyzed. Models for the Hf reported previously were mainly for circular burners which were not applicable for rectangular burners. For a given burner exit area and heat release rate, Hf firstly increases with the increasing of burner aspect ratio n from 1-1 to 7-1, and then decreases with the increasing of n from 7-1 to 71-1. For a given n , the projected vertical flame height Hf firstly increases (due to increase of fuel supply) and then de-creases (due to increase of horizontal momentum) with the increasing of heat release rate (HRR), showing an inherent transition behavior. The critical dimensionless HRR Q *critical (by employing the burner perimeter P as characteristic length scale) for this transition behavior decreases with the increased burner aspect ratio. A function was proposed for Q *critical of various burner aspect ratios. The normalized flame height, Hf / P , is well represented with the dimensionless heat release rate Q * when it is smaller than the critical value (Q *critical ). Meanwhile, for data with dimensionless HRR larger than the critical value, Hf/Hf,critical is well represented with Q /Q critical , where Hf , critical is the critical (maximum) projected vertical flame height at Q critical of transi-tional state. The present study provides new observations and fundamentals for the transitional behavior of vertical flame height of horizontally-oriented rectangular-source jet fires.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.