EXPERIMENTS ON IMPULSIVELY STARTED JET DIFFUSION FLAMES

The starting vortex of an impulsively generated jet diffusion flame wa s studied experimentally, Fuel jets were produced by the sudden discha rge via a solenoid valve into still air. The fuel jet was ignited by a pilot flame, The length and lateral spread of the flame were determin ed by video imaging. All flames were in the buoyancy-driven regime aft er the starting transient. The height at which tile starting vortex bu rned off completely was approximately the same as the mean flame lengt h of the subsequent steady flame. The penetration of the flame tip ass ociated with the starting vortex can be correlated by a buoyancy param eter derived from the isothermal starting plume theory of Turner. An u nexplained dependence of penetration on nozzle diameter was observed. The timescale for the mixing of the starting vortex at its maximum fla me height appears to be about one-half of the vortex rotation time at the same location, These findings may be useful in understanding unste ady combustion phenomena, especially as they pertain to active combust ion control schemes.