Experiments on the instability modes of buoyant diffusion flames and effects of ambient atmosphere on the instabilities

摘要: Large scale dynamic behavior of buoyant diffusion flames were studied experimentally. It was found that originating from circular nozzles exhibit two different modes flame instabilities. The first mode results in a sinuous meandering the flame, characteristic small diameter nozzles. This instability originates at some distance downstream nozzle exit contraction region envelope and develops into motion flame. second is varicose which very close to as axisymmetric perturbations contracting surface. In this mode, oscillations result formation toroidal vortical structures convect through cause periodic burn out top resulting observed height fluctuations. average heights are be typically shorter for these flames. oscillation frequencies their scaling also with having higher than mode. can switch one other probability observing appears increase increasing Richardson number. Additionally, feasibility altering explored variation oxidizer medium density. completely suppressed burning helium rich helium–oxygen mixtures. At lower concentrations, frequency significantly reduced. order enhance buoyancy effect, CO2–O2 mixtures studied. However, density its effects on compared those air. These experiments point towards under earth gravity studying large dynamical aspects without need variable environment.