We developed a new flameless combustion called swirling-RAI (reversed air injection) and evaluated through experiments and numerical simulation. In a circular furnace which has a specific purpose to heat pellet bed, two pair of nozzle sets from the concept of RAI are installed in the inversed direction against each other. Due to the high momentum of angled air nozzles installed axisymmetric, the overall flow in the furnace is swirling. The experiments showed methane-air combustion without flame and NO_x emission was 3 ppm while CO was not detected at the exit. The numerical simulation showed detail of flow and reaction in the S-RAI furnace to understand its phenomena. The experimental and simulation results are also compared to see the reliability of the simulation. The complexity of flameless combustion makes the proper simulation difficult. In particularly, oxygen concentration at Port 2 showed a difference. However, the simulation gives enough information of flow field and insight of its effect on the flameless combustion, which shows two recirculating flow patterns in the furnace; the first recirculation is occurring at the top due to the ejection effect of nozzle jets, and the second recirculation is located at the reducing cone under the nozzles which is due to swirling flow.
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