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Show environmental regulations. In the U.S., more than one-half of the N O x is from stationary sources (Wark and Warner, 1981). For example, high-temperature industrial furnaces generally need to maintain temperatures in excess of 1000°F for extended periods of time. To achieve these temperatures, the maximum flame temperature must exceed the demanded process temperature, greater than the 1800°F thermal-NOx "trigger" temperature. Such high temperatures cause industrial furnaces to emit significant amounts of N O x (Weakley, 1996). Two general NOx emissions control strategies can be applied to combustion sources: (1) reduction of N O x formation during the combustion process or (2) postcombustion control of N O x by flue gas treatment. The reduction of N O x formation during the combustion process can be achieved by one of three methods: (1) modification of combustion operating conditions; (2) modification of combustion equipment; or (3) fuel switching (USEPA, 1992). Fuel switching includes changing to a cleaner fuel such as natural gas. Industries are apparently making this move because a recent survey shows that industrial use made up 44.5% of gas usage in 1991 (Weakley, 1996). As demands for high performance increase, combinations of all three methods must be employed. Changes in operating conditions include running lean, and recirculating flue gas. Changes in combustion equipment include fuel injection strategies that mix the injected fuel rapidly with the combustion air. While the goal is to reduce NOx, combustion efficiency and combustion stability cannot be compromised Modifications to combustion equipment have been a focus of NOx research for more than two decades (Seinfeld, 1986). Testing and development of such equipment consists of trial and error experiments and, while effective, is time consuming and does not necessarily lead to the optimal configuration where multiple (sometimes coupled) variables are at play. Statistics-based "multivariate experiments" or "statistically designed experiments" are experimental tools that can be used in studying multiple variables. The multivariate study method has the advantage of being mathematically and statistically based. This tool can be used to set up a matrix of experiments to systematically test for an optimized response (Arellano et al., 1997). The present study evaluates the utility of a multivariate experimental approach for a commercial, low-NOx burner. BACKGROUND Current challenges in applying bench-scale results to full-scale systems have led to the design and construction of a full-scale, high-temperature furnace simulator at the U C Irvine, Combustion Laboratory (UCICL). The U C I C L furnace simulator has an internal dimension of 8 ft x 8 ft by 10 ft (length), surrounded by 11-inch thick blocks of ceramic fiber refractory, and encased in bolted panels of Vi-inch-thick carbon steel. The natural gas fired furnace simulator is designed for a maximum furnace temperature of 2400°F and a burner load of 4 M M BTU/hr. The simulator is equipped with two emission stacks to be 2 |