Flame stability and blow-off for Type I pulverized coal flames in a down-fired laboratory scale coal combustor have been investigated as a function of equivalence ratio and oxygen concentration. Flame stability was characterized by the primary oxidizer Reynolds number at flame blow-off. Four flames were investigated experimentally with varying molar oxygen concentrations in the non-swirl Primary Oxidizer (PO) and tangentially induced swirl Secondary Oxidizer (SO). These flames are represented as follows by mole fraction oxygen in PO/SO: 21%/21% (coal/air), 21%/30%, 21%/35%, 8%/35%. Numerical results assessing flame stability based on temperature and volatile reaction rates are presented for three of the experimental flames: coal/air, 21%/35%, and 8%/35%. Experimental results showed increased stability with increased equivalence ratio for each of the four flames. Increases in flame stability were most dramatic for flames with higher oxygen concentrations in the PO and SO. Blow-off inception for each flame with 21% oxygen in the PO was distinctly characterized by a sharp change in luminosity at the burner exit. While seemingly less stable than the coal/air flame, precise point of blow-off inception for the 8%/35% flame was less apparent due to the oxygen-enriched environment at the burner exit. Temperature profiles from the numerical model show improved flame holding for the 21%/35% conditions when compared to the coal/air and diluted PO case. Reaction rates also move closer to the burner exit at increased oxygen concentrations. For the 8%/35% flame the volatile reaction extends farther downstream indicating that dilution of the PO reduces the reaction rate and distributes the reaction over a larger region in the flame.

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