The work presents the assessment of a low emissions premixer/swirl burner configuration utilizing lean stratified fuel preparation. An axisymmetric, single- or double-cavity premixer, formed along one, two, or three concentric disks promotes propane-air premixing and supplies the combustion zone at the afterbody disk recirculation with a radial equivalence ratio gradient. The burner assemblies are operated with a swirl co-flow to study the interaction of the recirculating stratified flame with the surrounding swirl. A number of lean and ultra-lean flames operated either with a plane disk stabilizer or with one or two premixing cavity arrangements were evaluated over a range of inlet mixture conditions. The influence of the variation of the imposed swirl was studied for constant fuel injections. Measurements of turbulent velocities, temperatures, OH* chemiluminescence and gas analysis provided information on the performance of each burner set up. Comparisons with Large Eddy Simulations, performed with an 11-step global chemistry, illustrated the flame front interaction with the vortex formation region under the influence of the variable inlet mixture stratifications. The combined effort contributed to the identification of optimum configurations in terms of fuel consumption and pollutants emissions and to the delineation of important controlling parameters and limiting fuel-air mixing conditions. 1. Introduction Flow recirculation is exploited within combustion systems to promote fuel-air mixing, flame stability, and high efficiency over a wide range of operating conditions for modern power systems [1–3]. Plane or axisymmetric bluff-body stabilizers are popular arrangements for experimental and computational flame stabilization studies under nonpremixed [2, 4] and fully premixed configurations [5, 6]. Swirl motion is an equally common method of stabilization in industrial burners. Plane swirl can be regulated to create a free standing central recirculation zone (CRZ) for aerodynamic flame holding, while in combination with a bluff body allows for improved stability and emissions within reasonable residence times [2, 7]. In recent years, driven by more stringent regulations, new combustion technologies based on partially premixing the reactants to establish stratified, lean or ultra-lean operating conditions, have emerged as promising methodologies in the effort to achieve target efficiencies and emissions [3]. Nonuniformities in the fuel-air ratio offer design flexibility and are often exploited for a more effective management of fuel lean operation
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