Experimental Study On Swirl Characteristics Of The Low Swirl Injectors

The Low swirl Combustion (LSC) is a novel dry-low NOx combustion method that is being developed for gas turbines. Since the axial velocity decays rapidly in flow field, there is a position that the air current equals to the turbulent flame propagation velocity. In that position the gas turbines can achieve stable combustion. Low swirl injector (LSI) is a simple and highly adaptable technology to meet stringent emission standard without significantly altering the system configurations, or negative impact on efficiency, turndown, and costs.In this paper, the low-swirl injector is designed. Varying the blockage ratio of center perforated plates to control mass flux through center channel, thereby the swirl number can be changed. Using Fluent software to simulate and compute the mass flux ratio of the unswirled and swirled flows in different conditions. Then computing the swirl numbers of the different perforated plates assemble with swirlers.Then, using particle image velocimetry (PIV) system to investigate the LSIs’ cold state flow field by varying swirl numbers, bulk flow velocity and vane angle. Experimental results show that:(1) The LSIs show self-similarity features, and have nothing to do with the bulk flow velocity. With the rise of vane angle, the critical swirl numbers between high and low swirl flow increases. (2) Dimensionless axial velocity decays quickly along the axial direction, meanwhile the axial velocity decreases with increasing swirl number in the near field. In the low swirl state, dimensionless axial turbulent kinetic energy does not have significant effects on the swirl number. (3) With the rise of the swirl number, the turbulent kinetic energy of swirl flow zone increases significantly. When the swirl numbers are similar, the turbulent kinetic energy of unswirled flow field can increased by increasing the vane angle, the peaks of radial velocity get lower, and the distance between the two peaks are closer.Finally, an experimental facility which can used methane-air as fuel has been designed and set up. The combustion experiment at cp=0.7 has been done to investigate the effects of flame’s) shapes by changing swirl numbers, bulk flow velocity and vane angle. Experimental results show that:(1) Low swirl flames affected by the swirl number. With the swirl number increasing, the "W" shape flames gradually turns into "broom" shape. (2) Maintained vane angle of the swirlers at the same numerical value, the length of low swirl flame can be reduced and the lift off heights are closer to the nozzle by increasing the swirl number,. In the case of swirl number are close to the flame shape there are significant differences. While the swirl numbers are similar, There are significant effects on flame shape by varying the vane angle of LSIs.