Hermanson, James Carl
Localized preheating of a premixed lean fuel/air flow was examined experimentally to determine its effects on flame stability and NOx emissions. Restricting heating to the fuel/air flow entrained behind a bluff body by heating the flameholder requires significantly less energy than preheating the entire fuel/air mixture. The constructed experimental apparatus consisted of four major sections: the flow straightening section, the combustion chamber, contract nozzle and the exhaust and emissions isolation section. In the combustion chamber, the fuel/air mixture was entrained into the wake of small bluff body flameholder where the flame was stabilized due to the recirculation of hot combustion gases. The fuel was ethylene and the combustor pressure was approximately one atmosphere. The inlet fuel/air mixture was upstream of the flameholder and was adjusted to give equivalence ratios ranging from [phi]=0.37 to [phi]=0.55. The Reynolds number was also varied from 2,500 to 10,000. The impact of flameholder heating on flame stability was determined by visually observing lean blow-off, while exhaust plane temperature was measured downstream from the combustion process. The localized heating produced by the flameholder heater was observed to increase the flame stability by decreasing the lean blow-off limit by approximately 20%. The exhaust plane temperature data obtained indicated a significant decrease in flame temperature. The increased flame stability coupled with the significant decrease in flame temperature suggests the potential benefits of flameholder heating in reducing NOx emissions.
Worcester Polytechnic Institute
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