Abstract
The stabilization of propane-air flames in adiabatic, refractory tubes without a flameholder was investigated experimentally. The tubes were 3/16-in and 3/8-in diameter and 10-in long, and the flow rates extended into the laminar and turbulent regions. Radial heat losses were minimized by combustion in surrounding tubes. The transient temperature at six points along the tube wall was measured for a series of lean fuel-air ratios as the flow ratio was varied in steps from the flashback limit to the blow-off limit. The stable flame velocities and the range of stable flame velocities increased with tube diameter and to a lesser extent with fuel-air ratio. The blow-off limits are much higher than those for laminar and turbulent bunsen flames but are less than those for heated flat plates or bluff-body flameholders. Combustion was essentially flameless. Oscillations and acoustic generation were noticeable only near the stability limits. The peak in the wall temperature profile moved downstream with increasing flow rate and decreasing fuel-air ratio. The stability limits were reproducible but the temperature profiles were somewhat variable indicating possible multiple stable states. The consistency of the results with thermal and kinetic considerations suggests that a mathematical model can be developed to explain the observed effects ad to predict behavior for other conditions and fuels.
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