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Show 5 operate at a load of 25 Mw/m2, which is more than 5 times the 1.6 maximum load of the non-po-rous one. Regarding the air ra- 1.5 --IJ- [D1-P5,P] Rich limit --0- [D1-P5,P] Lean limit --.- fD1-P5,N] Rich limit ~ D1-P5,N] Lean limit tio, even at an air ratio of 1.5, the perforated porous burner 1.4 0 provides good flame stability at ;: a3 1.3 a load of 5 Mw/m2, which a: ~ means that the NOx level is very <i 12 low. It should be noted that Perforated Porous Blow off )/ Perforated non-porous even though the flame port ge- 1.1 ometry is the same for the two burners, the difference in the 1 burner material greatly affects 0 5 10 15 20 25 the combustion performance. Combustion Intensity [MW 1m2] Fig. 5 Comparison of combustion range of two burners Percolation rate through porous plate The perforated porous burner has an extremely high flame stability possibly because of the percolation effect from the porous surface other than the flame ports. The port flow rate and the percolation flow rate were therefore estimated by the following measurements. First, the total flow rate of the perforated porous burner was measured at each burner pressure. The flow rate of the stainless plate burner perforated in the same way was also measured. Then, the difference of the two flow rates is considered to be the percolation flow rate. Figure 6 shows the relation between the burner internal pressure and each flow rate for the perforated porous plate shown in Fig. 4. The percolation flow rate from the porous plate is clearly higher than the port flow rate, and accounts for about 700/0 of the total flow. The percolation flow thus plays an important role in the flame stabilizing mechanism. The flow balance between the port and percolation flow varies with port diameter and port spacing. |