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Show reference also discusses new recent evidence on the C H + N 2 rate coefficient from other experiments and theoretical calculations. W e recommend an adjustment of the value used in GRI-Mech by a factor of 2.1. REBURN CHEMISTRY Reburn is an important and impressively useful strategy for reducing NO when it is produced in high concentrations (hundreds of p p m or more) in burner systems. Natural gas is injected downstream and removes N O initiated by the C H + N O reaction. (Proper staging can even reduce N O in already low-NOx burners at, e.g., 30 ppm.) A n examination of reburn chemistry in our low pressure flames is again facilitated by the fact that w e know C H concentrations well. Table 1. Flame Conditions and Prompt N O Results Flame O Pressure (torr) %N2 Measured N O (ppm) Model N O k'/k Peak C H k'/k Integrated C H k'/k Lean 0.80 25 65.3 7.0±1.0 2.8 3.710.7 3.50 3.8 Standard 1.07 25 59.9 17.5±0.7 8.5 2.7±0.1 2.88 2.54 Rich 1.27 30 58.2 37.4±4.4 22.7 1.8±0.2 2.20 2.11 Incr. N2 1.27 30 61.6 39.6±2.7 25.5 1.7±0.1 2.00 1.97 Deer. N2 1.27 30 52.4 34.2±3.7 22.8 1.7±0.2 2.02 1.73 N O was seeded into the Lean and Rich flames at concentrations between 500 p p m and 30000 p p m (3%), and again measured at 2 c m above the burner surface. At high seeding levels measurements must be made in the (0,1) band of the A-X system to avoid optical depth problems in (0,0). 16 The LIF measurements of concentration are shown as a function of seeding level in Fig. 2, with the Lean and Rich flames on the same scale. Determination of a calibration level for no reburn requires care. W e know that reburn is less for lower seeding levels and lower flames. For the lowest levels the model predicts reburn of 2 % , 3 % , and 6%. W e use these lowest levels in the heat flame, corrected by the model prediction, to establish a zero-reburn line. Details are presented in Ref. 16. 50 -r 0 1 2 3 Mole % N O seeded in (corrected for dilution) Figure 2. Measured (points) and predicted (lines) N O reduction in the Rich (upper) and Lean (lower) flames. 7 |
