Performance enhancement of inverse diffusion flame burners with distributed ports

Abstract

An experimental study regarding the influence of the air port design on the inverse diffusion flame characteristics was performed for two different burner configurations, wherein the combustion/heat transfer performance was optimized. In the first configuration that comprised a single air port and distributed fuel ports, decreasing the air jet diameter enhanced the combustion efficiency by 3.6% as testified by recording a maximum decrease of 81.3% in the CO emissions. As the central air jet Reynolds number thus reached 18038, the stability limit was extended by 181% in terms of the air jet velocity; while the flame length was reduced by 38.6%. Inasmuch as the flow residence time across the high-temperature zone thus decreased, NO x emissions as low as 6 ppm were obtained. In the other configuration that had multiple air ports, there was a decrease in the CO, HC, and NO x emissions respectively by 69%, 58%, and 31% in comparison to those of the single port having the same port area. It was found that the smallest jet diameter was accompanied by the highest peak temperature as well as the maximum heat flux to a plate on which the flame impinged, respectively, having the values of 1761℃ and 11.4 kW/m2. In this regard, increasing the air jet Reynolds number by 30% increased the peak flame temperature by 8.3%. In the primary equivalence ratio range between 0.8 and 2.0, the impingement plate optimum spacing for the maximum heat flux was found to correlate well with Reynolds number. Combining the nonunity Lewis number and the Gas Research Institute-3 (GRI-3) kinetics with the k − ɛ model verified the fuel jet deflection and soot development, but overpredicted the NO x emissions by 11.5%. Increasing the center-to-center distance between the central air jet and the distributed fuel ports reduced the flame length by 19%.