Abstract
The objective of this study is to investigate the flame-interaction and to design a multi-ring combustor with optimal performance. The flame-interaction was controlled by varying gap ratio (S/d) and equivalence ratio (□). Their effects on the flame structure were investigated by numerical and experimental methods. The sudden expansion structure of multi-ring combustor generate the flame holding and preheating effect, these phenomena can provide combustor operate in the fuel lean condition. The optimal operation conditions are S/d = 1.67, the inner ring □ = 0.8, and the middle and the outer ring □ = 1.1, which is corresponded to the objective of high performance and low pollutant. The change of geometric dimension by varying S/d greatly affects the flame structure, where different degree of flame-interaction can be found. When S/d = 1.0, the flame merge together because the gap distance is short, and the separated ring-flame cannot be observed. This phenomenon will cause decrease reaction area and the preheating effect can not be provided to unburnt gas near the exit region of the combustor. Thus, the combustion rate can not be improved effectively. Considering the emission production, despite the production of carbon dioxide is lower, the production of nitric oxides(NOx) is the highest. When S/d = 1.67 and 2.33, a separated ring-flame can be found on each of the rings since the gap distance is wider. Similar flame pattern can also be found among ring-flames. Furthermore, their productions of NOx are nearly equal. This is because the effects of flame-interaction on flame structure rapidly decrease when the gap ratio increases beyond a specific value. The equivalence ratio dominates the initial flame strength and characteristic; consequently, it influences the flame-interaction. When □ = 1.1, the flame strength is the strongest and temperature is the highest. Although the production of NOx is slightly higher than that of □ = 1.3 and □ = 1.5, its global performance is the best.