On Flame Stability In The Hysteresis Regime In Co-Flow

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Title: On Flame Stability In The Hysteresis Regime In Co-Flow
Author: Terry, Stephen D
Advisors: Richard Johnson, Committee Member
Joel DuCoste, Committee Member
William Roberts, Committee Member
Herbert Eckerlin, Committee Member
Kevin Lyons, Committee Chair
Abstract: This study documents experiments performed on lifted turbulent diffusion flames in the hysteresis regime with air co-flow. Undiluted methane, ethylene, and propane were used as fuels and two nozzle sizes were used. The results confirm the non-linearity of the lift-off height with nozzle velocity, showing a previously undocumented region where lifted flame height increases as fuel velocity is decreased and that reattachment nozzle velocity varies linearly with co-flow. Using jet relations from Tieszen, the local excess jet velocity was computed and found to vary linearly for flames lifted well above the nozzle. The effect of co-flow was captured using an effective local excess jet velocity, similar to the effective nozzle jet velocity proposed by Montgomery used in conjunction with the results of Khalghatgi. Local excess jet velocities at the reattachment point were also compared for varying co-flow and found to be consistent between co-flow cases. This threshold velocity was found to vary with the inverse of the laminar burning velocity of the fuel squared. Relations for reattachment nozzle velocity and flame lift-off height at reattachment were also determined. The results extend the work of Khalghatgi into the hysteresis regime and complement the work of Gollahalli in determining the mechanisms that support flame stability in the hysteresis regime. Any comprehensive theory for flame stability will have to explain some of the unexpected results seen in the hysteresis regime and incorporate the findings of this study.
Date: 2005-04-19
Degree: PhD
Discipline: Mechanical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/5652

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