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Show 9 SUMMARY AND CONCLUSIONS The results reveal the sensitivity of burner performance to the preparation of the fuel-air mixture. In the present case, three types of radial injectors are compared: 1) straight radial jets, 2) counter-swirling radial jets, and 3) co-swirling radial jets. The nozzles show different emissions characteristics and stability limits. A performance function is introduced to compare conditions for each nozzle and between each nozzle. The counter-swirl nozzle shows the most promising performance at excess air levels near 20% and swirl values in the range of 0.66-0.68. The conclusions reached for the present studies are • As regularly observed in practical applications and laboratory burners, a reduction in NOx in the present model industrial burner is accompanied in general by a reduction in combustion efficiency. • Noteworthy, however, is that fuel-air mixing conditions are identified (albeit limited) for which NOx is reduced without a compromise to combustion efficiency. • While the mechanism for this behavior is not presently understood and likely complicated by a combination of turbulent mixing, heat release, and turbulent-chemical interaction, the results show promise for improved designs. • For the present study, the counter-swirl nozzle reveals the peak performance of those interrogated, with a maximum of performance at 22.50% excess air and a swirl intensity of 0.68. • Not only are the optimal conditions limited in number, but they undoubtedly change as a function of load and lifetime of the burner. In addition, the conditions for optimum performance can occur (as in the present experiment) near the lean stability limit. As a result, the application of active control appears prudent as a vehicle for both the attainment and maintenance of optimal performance. • The flexibility of the performance function provides the ability to address regional and internal requirements regarding emissions and efficiency. ACKNOWLEDGMENTS The program described is supported by the California Institute of Energy Efficiency (CIEE) with Dr. Diane Fisher as the Program Monitor, and the Southern California Gas Company with Mr. Cherif Youssef as the Program Monitor. Weare indebted to the advice and counsel of a twenty-five member Advisory Committee, and to five colleagues who have devoted time and energy in critiquing both the burner design and test protocol: Dr. Richard Waibel (John Zink), Mr. Steve Londerville (Coen), Mr. Barry McDonald (CARNOT), Mr. Thomas Judson (Webster), and Dr. Roy Payne (EER). Special thanks are extended to Mr. David St. John for his assistance in |