Preliminary Study of Reacting Flow Field in A Burner with Cap-induced Premixing Combustion

Abstract

The reacting flow fields of a bluff-body combustor and a newly devised cap burner were investigated. To understand the flame structure, methods based on particle image velocimetry (PIV) and chemiluminescence were adopted to detect the flow structure and local intensity of flame radiation, either individually or synchronically. In addition, the distribution of temperature was obtained by thermocouple measurement. In the study for a bluff-body burner, the flame pattern, with increasing central fuel-jet velocity at fixed annular air-flow velocity, was classified into three modes: recirculating flame, jet-dominated flame, and jet-like flame. The position of flame front was dependent on the flow field. When the velocity of fuel jet was increased, the recirculation zone became shrunk and in turn affected the formation of combustion region. The temperature profiles showed that the recirculation zone provided a heat source for downstream flow and the ignition was facilitated by the recirculating flow. In the study for the cap burner, the flammable limit indicated an expanded range of fuel jet velocity. This was due to the stabilization and induced near-premixing effects of the cap. The experimental results were compared with numerical simulations. The distributions of velocity, temperature, and specific radicals like CH and OH can thus be studied in depth. This reveals advantages of the cap device over the traditional burners and direction for further improvement of the structure that can significantly enhance the mixing process and combustion efficiency. NomenclatureD j = mass diffusivity P = pressure T = temperature U = flow velocity U j = central fuel jet velocity U a = annular air flow velocity  = fluid density  = surface tension of liquid  = fluid viscosity