On the bi-stable nature of turbulent premixed bluff-body stabilized flames at elevated pressure and near lean blow-off
AuthorsSkiba, Aaron W.
Roberts, William L.
KAUST DepartmentClean Combustion Research Center
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
high-pressure combustion (HPC) Research Group
KAUST Grant NumberBAS/1/1370-01-01
Online Publication Date2020-08-14
Print Publication Date2020-08
Embargo End Date2022-08-14
Permanent link to this recordhttp://hdl.handle.net/10754/664616
MetadataShow full item record
AbstractThis study considers turbulent premixed bluff-body stabilized flames at elevated pressures. Specifically, the lean blow-off (LBO) limit of such flames is determined for a range of bulk velocities (5 ≤ U ≤ 50 m/s) and operating pressures up to 3 bar. Two key observations emerge from this stability assessment. The first is that considering elevated pressure leads to two stability regimes: one at atmospheric conditions and those with elevated pressure and U ≳ 20 m/s (regime-a), and another at elevated pressures with U ≲ 20 m/s (regime-b). The second observation is that within these regimes, LBO limits are insensitive to pressure. Flames in regime-a (S-flames) are found to be more stable than those in regime-b (U-flames). Advanced image-based diagnostics were employed to understand reasons for this difference in stability. Flow field measurements indicate that U-flames are associated with an outer recirculation zone (ORZ) that formed as pressure increased but receded from the burner as U surpassed ∼ 20 m/s. PLIF images of CH2O and OH demonstrated that the ORZ interacts with U-flames such that their downstream regions are prevented from collapsing to the inner recirculation zone (IRZ). Furthermore, analysis of the OH-PLIF images indicate that U-flames possess larger turbulent consumption rates, helping them form large IRZs and rendering them more susceptible to influence from the ORZ. Results of high-speed OH* imaging demonstrate that LBO events differ between U- and S-flames. Namely, while S-flames collapse to their IRZs during LBO, U-flames lift off from the burner, depleting their anchoring regions of reactions and hot products. Losing back-support in this region is what ultimately reduces the stability of U-flames. Finally, the reason U-flames lift off from the burner during LBO is elucidated by joint flow-flame measurements. Specifically, the anchoring regions of U-flames reside in regions of large axial velocity, which likely stems from their enhanced burning rates.
CitationSkiba, A. W., Guiberti, T. F., Boyette, W. R., Roberts, W. L., & Mastorakos, E. (2020). On the bi-stable nature of turbulent premixed bluff-body stabilized flames at elevated pressure and near lean blow-off. Proceedings of the Combustion Institute. doi:10.1016/j.proci.2020.06.060
SponsorsThe research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST; grant number: BAS/1/1370-01-01).