The Impact of Swirling Flow Strength on Lean-Dome LDI Pilot Mixers’ Operability and Emissions
Authors: X. Ren, X. Xue, K. B. Brady, C. J. Sung, and H. C. Mongia
Direct link to the paper: https://doi.org/10.1016/j.expthermflusci.2019.109840
In an effort to reduce the environmental impact of aviation, lean-dome combustion concepts such as lean direct injection (LDI) are being pursued for their potential to achieve very low emissions. However, low-emissions potentials may be accompanied by operability challenges. In the present effort – part of a series of fundamental investigations into LDI operability challenges – systematic experiments of lean-dome-relevant pilot combustor devices are conducted in a single-element methane-fueled combustor test rig with two different LDI configurations by using a suite of optical diagnostics. While maintaining all other design features constant, the clockwise vane angle of the outer air swirler is altered between 60° (LDI-60-CW configuration) and 45° (LDI-45-CW configuration), representing strong and weak swirling flows, respectively. Measurements of the non-reacting/reacting flow fields and flame characteristics are performed as a function of overall equivalence ratio via time-resolved particle image velocimetry, OH*/CH*/NO2* chemiluminescence, OH planar laser-induced fluorescence, and broadband flame imaging. It is found that a large center recirculation zone exists only with the LDI-60-CW configuration, while the LDI-45-CW flow is dominated by a swirling jet flow. In addition, it is shown that the center recirculation zone in the LDI-60-CW configuration results in noticeably lower lean blowout limits than the LDI-45-CW configuration, but at the cost of much higher NOx production for vigorously-burning equivalence ratios. At lower equivalence ratios near lean blowout conditions, both configurations result in similar NOx production. These results are discussed in terms of identifying possible research directions for optimizing LDI designs for reduced NOx emissions while maintaining or improving operability relative to current rich-dome combustion technology.
Citation: X. Ren, X. Xue, K. B. Brady, C. J. Sung, and H. C. Mongia, “The Impact of Swirling Flow Strength on Lean-Dome LDI Pilot Mixers’ Operability and Emissions,” Experimental Thermal and Fluid Science 109, 109840 (2019).