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One of the most promising methods for reducing NOx emissions of jet engines is the lean combustion process. In order to realize this concept the percentage of air flowing through the combustor dome has to be drastically increased. This requirement leads to nozzles with high effective area and to high mean velocities in the primary zone of the combustor chamber. The investigation of the lean blow out limit for those nozzles is of main interest for the design of lean combustor technology. It is reported on investigation of a kerosene-fueled, swirl stabilized flame at atmospheric conditions. Two lean operation conditions are investigated, one in stable regime and the other very close to the weak extinction limit. It has been determined, that the flame shape changes when shifted from the stable regime to the other one close to the weak extinction limit (also referred to further as LBO — lean blowout). Since all field measurement schemes are similar, the gained data can be associated and conclusions regarding the flame stabilization at lean conditions can be drawn. The velocity data yields information about the topology of both isothermal and reacting flow fields in the combustion chamber. The internal recirculation and the corner recirculation zones can be well distinguished, because it can be measured directly in the nozzle exit plane. The comparison of the experimental data at stable and near LBO conditions shows the importance of inner and outer recirculation zones for the stabilization process. Furthermore, a comparison with a gaseous fuel nozzle will exhibit the differences between liquid and gaseous fuel combustion.

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This paper presents the reacting flow field and the temperature distribution of two different airblast nozzles, namely co and counter swirl. To support the interpretation of the obtained results, previous measurements of the isothermal flow and mixture field of methane and combustion air are summarized. Velocities within the turbulent flow field were measured by using 3D-LDA, measurements of the field distribution of temperature were performed by means of thermocouple probes. The results show that the counter swirl arrangement provides formation of an additional vortex in the immediate vicinity of the nozzle, which has been observed as well within the isothermal as within the reacting flow. Furthermore, a dampening effect of the tangential velocity profiles towards turbulent exchange of momentum has been observed within the counter swirl configuration. Both effects cause preferential mixing of the fuel with the inner combustion air flow, thereby performing higher concentrations of methane in the near nozzle mixture field. As a consequence the counter swirl flow field exhibits larger areas of near-stoichiometric composition of fuel and air, resulting in an elevated temperature level within the stabilization zone at otherwise identical operation conditions. Therefore, application of a counter swirl nozzle allows a higher thermal load than the co swirl configuration, which offers a satisfying explanation for the wider operating range of the counter swirl burner.