Experimental investigations and large-eddy simulation of low-swirl combustion in a lean premixed multi-nozzle combustor

This paper presents laser diagnostic experiments and large-eddy simulations (LES) of low-swirl lean premixed methane/air flames in a multi-nozzle combustor including five nozzles with the same structure. OH planar laser-induced fluorescence is used to observe flame shapes and identify main reaction zones. NOx and CO emissions are also recorded during the experiment. The flows and flames are studied at different equivalence ratios ranging from 0.5 to 0.8, while the bulk inlet velocity is fixed at 6.2 m/s. Results show that the neighboring swirling flows interact with each other, generating a highly turbulent interacting zone where intensive reactions take place. The flame is stabilized above the nozzle rim, and its liftoff height decreases with increasing equivalence ratio. The center flow is confined and distorted by the neighboring flows, resulting in instabilities of the center flame. Mean OH radical images reveal that the center nozzle flame is extinguished when equivalence ratio is equals to 0.5, which is successfully predicted by LES. In addition, NOx emissions show log-linear dependency on the adiabatic flame temperature, while the CO emissions remain lower than 10 ppm. NOx emissions for multi-nozzle flame are less sensitive to the flame temperature than that for single nozzle. These results demonstrate that the low-swirl multi-nozzle concept is a promising solution to achieve stable combustion with ultra-low emissions in gas turbines.