Effects of heating height on flame appearance, temperature field and efficiency of an impinging laminar jet flame used in domestic gas stoves

摘要

Laminar jet flames are used in most domestic gas burners. However, the literature on combustion characteristics and thermal efficiencies of a single laminar impinging jet flame is very limited. Heating height is a significant operating parameter of a domestic gas stove, but it has received little attention in the literature. In this study, our aim is to simulate and examine the effect of heating height on the flame characteristics of a domestic gas stove. We emphasize the importance of heating height on flame structure, temperature distribution and thermal efficiency for low-Reynolds-number fuel-rich methane-air flames impinging normal to a plane surface, which has not been documented yet. Results show that flame structure, temperature distribution and thermal efficiency are greatly influenced by the heating height. With increasing heating height, the thermal efficiency first increases to a maximum value and then decreases. An optimum heating height, identified by the widest high temperature zone and the highest thermal efficiency, is achieved under the condition of Type-C flame burning, in which both the inner premixed flame and outer diffusion flame are open and diverge. Furthermore, we find that the optimum heating height increases with increasing methane concentration or injection velocity. Note that the maximum thermal efficiency occurs when the heating height is slightly lower than the tip of the inner rich premixed flame. This important characteristic can be applied to the design of domestic gas stoves, and it was not found in the available published work.