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Show Near-Burner Flow-Field Characterization and Its Relation to Performance in a Model Industrial, Natural Gas Fired Burner M. M. Miyasato and G. S. Samuelsen UCI Combustion Laboratory University of California, Irvine Irvine, CA, 92717-3550 USA In-flame NOx control techniques rely on lowering combustion temperatures to reduce thermal NO. These techniques can also lower combustion efficiency by compromising CO and hydrocarbon burnout. To address the "trade-off' between NOx and combustion efficiency, different fuel injector strategies are employed, and flue gas measurements are acquired for a range of excess air and swirl intensities in a natural gas fired, model industrial burner. A performance function is defmed to· identify conditions suitable for detailed measurements of the flow-field. Non-intrusive, laser anemometry measurements are conducted at three axial locations downstream of the burner exit for seven conditions to quantify the flow-fields and recirculation zones. The results suggest that, in addition to percent recirculated mass, the complex processes of near-field fuel and air mixing have a significant impact on NOx emissions and the maintenance of high combustion efficiency. INTRODUCTION Emissions of nitrogen oxides (NOx) from industrial burners are being regulated to ever lower levels, especially in southern California where the prevalent atmospheric conditions and high population density combine to produce a major urban air quality challenge [1]. Techniques to reduce NOx include diluent injection, staged combustion, and lean bum operation [2]. A complementary strategy is to tailor the fuel and air mixing processes [3-6]. These strategies, unfortunately, can lead to a corresponding reduction in combustion efficiency due to reduced CO burnout, and a "trade-off' between NOx and CO can thereby occur. This is illustrated in Figure 1 where, for a given load condition, NOx is reduced by modifying the excess air and swirl strength in a natural gas fired burner. While successful in NOx reduction, the combustion efficiency is compromised. This paper investigates different fuel and air mixing strategies to achieve, for a given load, low NOx without sacrificing CO. A model, industrial burner is used, and in-situ measurements are acquired at select operating conditions to (1) detail the burner aerodynamics, (2) quantify the percent recirculated mass, and (3) gain insight into the relationship of fuel and air mixing strategies to overall burner performance. |