562015-03-24 , 法政大学大学院理工学・工学研究科
Emissions characteristic of Reverse Flow Flame Stabilized Combustion was investigated with the aim of applying it to the first stage of a multi stage lean combustor for attaining single digit NOx emissions while maintaining complete combustion over a wide range of gas turbine power. Homogeneous methane-air mixt ures were injected toward the dome of a cylindrical ceramic combustion chamber from a coaxially located tubular injectors with different nozzles at mixture or air(non-premixed case) temperature ranging from 373 to 573 K, and injection velocities of air ranging from 25 to 50 m/s. Tests were conducted for different injection points, and for different gas sampling positions above injection points at equivalence ratios from 0.7 to a value very close to the blow-off limits. Additional experiments were conducted with non-premixed system.Single digit NOx emissions were obtained with all premixed cases at leaner conditions with combustion efficiencies greater than 99.9.The NOx emissions for non-premixed cases were higher than for premixed cases.The injector configurations and the distance from the injection point to the dome wall were critical factors for flame holding: with the premixed case injector producing a strong swirling jet, injection positions of 80 and 130mm from the dome wall, no flames were established, even when mixture was riched up to correctfuel-air composition. For premixed case, the single hole injector was able to hold at leaner conditions than swirl-type injector while its NOx emissions level was slightly higher atlarger equivalence ratios than those achieved with swirl-type injectors. The NOx emissions were practically independent of injection velocity or combustor residence time over the whole gas temperatures tested. The effects of operating parameters on flame holding and NOx emissions were discussed based on direct flame images and predictions by simple simulations of iso-thermal flows in the combustor with different injector configurations.