Instability transition of a jet diffusion flame in quiescent environment

Abstract This paper studies the instability transition of a jet diffusion flame in quiescent environment. Previous study reported the existence of two instability modes, varicose and sinuous, based on their dynamical features. To provide a uniform classification, which allows for quantifications of not only the two instability modes but also the transition between them, we propose a new criterion based on the flame symmetry. Applying this quantification, we show that the instability of diffusion flames transitions from symmetric to asymmetric modes with increasing fuel rate or decreasing nozzle diameter. To explore the essence governing this transition, we performed dimensional analysis and identified two parameters, the Froude number (Fr) and the Reynolds Number (Re). The effect of the latter on the mode transition of jet diffusion flames has not been discovered previously. The regime diagram plotted on the Re-Fr parameter space verifies that the instability transition of jet diffusion flames is dictated by these two parameters, with Fr dominating the buoyancy-driven flames and Re dominating the momentum-driven flames.