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Show the role of fuel and air mixing on NOx production and to identify steps that can be taken in the design and operation of gas flred burners to minimize NOx production through the optimization of fuel and air mixing. At the UCI Combustion Laboratory (UCICL), experimental studies are being conducted on model industrial, natural gas flred burners to study the effect of geometric and flow parameters on fuel-air mixing and NOx minimization with the requirement of maintaining high combustion efficiency. In addition, the Lawrence Livermore National Laboratories (LLNL) , the Sandia National Laboratories, Livermore (SNLL), and Energy and Environmental Research Corporation (EER) are contributing their expertise to the program in the flelds of comprehensive combustion modeling, advanced laser diagnostics, and practical industrial application, respectively. The LLNL is modeling the flow field and species concentration profiles corresponding to the experimental test matrix of the burner at the UCICL, while the SNLL is developing a laser diagnostic (Degenerate Four Wave Mixing, DFWM) to measure in-flame nitric oxide (NO) and nitrogen dioxide (N02) concentrations. Both tools (i.e., the modeling and the DFWM) will help to quantify and better comprehend how fuel and air mixing affects NOx production. BACKGROUND It is well established that in combustion systems where air serves as the oxidant, thermal NOx is formed, even at overall lean equiValence ratios. Because the fuel and air generally have only a short temporal and small spatial extent to mix before reaction, a distribution of fuel and air "packets" develop of varied equiValence ratios which react before they can be unifonnly mixed. Previous studies have shown that the fuel-air mixing strongly affects the burner emissions (Appleton and Heywood, 1973 and Gupta, Ramavajjala, and Taha, 1992). Oaypole and Syred (1981) also concluded that reduced NOx emissions found in one of their flame conditions was probably the result of better mixing and less fuel rich regions. Intuitively, this implies that the burner geometry, which dictates the aerodynamics and subsequent fuel-air mixing, is an important factor in burner emissions. Other researchers have investigated peripheral fuel injection as a means to improve mixing (Beltagui and MacCallum, 1988) and lower NOx production (Ahmad, Andrews, and Sharif, 1984). In addition, a study conducted by the IFRF (Heap, Lowes, and Walmsley, 1973) demonstrated that tailoring the fuel ~jector angle, axial location of the injector, and swirl intensity can reduce NOx emissions. From these results, it can be intimated that the decrease in thermal NOx is caused by a more uniform distribution of the fuel and air, reducing the number of local "hot spots" by approaching an equivalent of a premixed system. Semerjian, Ball, and Vranos (1978) and Fric (1992) showed that decreased equivalence ratio fluctuations and decreased concentration fluctuations of a seeder species, respectively, resulted in decreased NOx emissions. In both cases, the mixing was achieved by providing a "premixing" distance between the fuel injector and the flame holder. Low fluctuations were considered a measure of high fuel-air uniformity. A similar study was conducted by Hase and Ohgi (1989) in which they found that large temperature fluctuations affect the NOx emissions causing deviations from the premixed case. These studies show that fuel and air mixing affects N Ox production through the flow field aerodynamics, which is dictated by the burner geometry. If the fuel and air are introduced such that uniform mixing occurs prior to combustion with low temperature 2 |