TY - JOUR
T1 - Experimental and computational study of soot evolution in a turbulent nonpremixed bluff body ethylene flame
AU - Mueller, Michael E.
AU - Chan, Qing N.
AU - Qamar, Nader H.
AU - Dally, Bassam B.
AU - Pitsch, Heinz
AU - Alwahabi, Zeyad T.
AU - Nathan, Graham J.
N1 - Funding Information:
The American authors gratefully acknowledge funding from the National Aeronautics and Space Administration (NASA) and the Strategic Environmental Research and Development Program (SERDP). The Australian authors gratefully acknowledge funding from the Australian Research Council (ARC) through the Discovery and the Linkage Infrastructure, Equipment, and Facilities (LIEF) grant programs. In addition, M.E.M. gratefully acknowledges funding from the National Defense Science and Engineering Graduate (NDSEG) Fellowship and the National Science Foundation (NSF) Graduate Research Fellowship Program.
PY - 2013/7
Y1 - 2013/7
N2 - A turbulent nonpremixed bluff body ethylene flame is studied both experimentally and computationally. Experimentally, the soot volume fraction is measured using laser-induced incandescence (LII). Three distinct regions are observed in the flame: a low-strain recirculation zone, a downstream jet-like region, and a high-strain neck region connecting these two regions. The maximum soot volume fraction is found in the recirculation zone, but most of the soot volume is contained in the larger jet-like region further downstream. In the neck region between these two zones, soot cannot form due to large strain rates, and the small amounts of soot in this region indicate that soot rarely escapes the recirculation zone before being oxidized. The recirculation zone is characterized by a low soot intermittency, in contrast to the downstream jet-like region and previously investigated jet flames in which the soot intermittency is high. Large Eddy Simulation (LES) is used to further investigate this distinctly different evolution of soot in the recirculation zone. The LES model is found to predict the soot volume fraction profiles quite accurately, albeit with significant sensitivity to the inflow profiles of the fuel jet and air coflow. Soot is formed near the inner shear layer between the fuel jet and recirculation zone where the mixture fraction is sufficiently large to support Polycyclic Aromatic Hydrocarbon (PAH) formation. A portion of this soot is entrained into the interior of the recirculation zone where the soot growth rates are relatively low, despite the rich mixture fraction in this region. The circulation vortex then transports the soot from the interior of the recirculation zone toward less rich mixture fractions near the flame, which is situated in the outer shear layer between the air coflow and the recirculation zone. Here, the majority of soot growth occurs due to surface growth, that is, mass addition due to surface reactions with acetylene. The dominance of acetylene-based surface growth in the recirculation zone contrasts findings in previous simulations of turbulent jet flames that do not exhibit a recirculation zone, in which nucleation and PAH condensation were found to overwhelm acetylene-based surface growth.
AB - A turbulent nonpremixed bluff body ethylene flame is studied both experimentally and computationally. Experimentally, the soot volume fraction is measured using laser-induced incandescence (LII). Three distinct regions are observed in the flame: a low-strain recirculation zone, a downstream jet-like region, and a high-strain neck region connecting these two regions. The maximum soot volume fraction is found in the recirculation zone, but most of the soot volume is contained in the larger jet-like region further downstream. In the neck region between these two zones, soot cannot form due to large strain rates, and the small amounts of soot in this region indicate that soot rarely escapes the recirculation zone before being oxidized. The recirculation zone is characterized by a low soot intermittency, in contrast to the downstream jet-like region and previously investigated jet flames in which the soot intermittency is high. Large Eddy Simulation (LES) is used to further investigate this distinctly different evolution of soot in the recirculation zone. The LES model is found to predict the soot volume fraction profiles quite accurately, albeit with significant sensitivity to the inflow profiles of the fuel jet and air coflow. Soot is formed near the inner shear layer between the fuel jet and recirculation zone where the mixture fraction is sufficiently large to support Polycyclic Aromatic Hydrocarbon (PAH) formation. A portion of this soot is entrained into the interior of the recirculation zone where the soot growth rates are relatively low, despite the rich mixture fraction in this region. The circulation vortex then transports the soot from the interior of the recirculation zone toward less rich mixture fractions near the flame, which is situated in the outer shear layer between the air coflow and the recirculation zone. Here, the majority of soot growth occurs due to surface growth, that is, mass addition due to surface reactions with acetylene. The dominance of acetylene-based surface growth in the recirculation zone contrasts findings in previous simulations of turbulent jet flames that do not exhibit a recirculation zone, in which nucleation and PAH condensation were found to overwhelm acetylene-based surface growth.
KW - Bluff body flame
KW - Large Eddy Simulation
KW - Laser-induced incandescence
KW - Soot
KW - Turbulent nonpremixed flame
UR - http://www.scopus.com/inward/record.url?scp=84876722698&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84876722698&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2013.02.010
DO - 10.1016/j.combustflame.2013.02.010
M3 - Article
AN - SCOPUS:84876722698
SN - 0010-2180
VL - 160
SP - 1298
EP - 1309
JO - Combustion and Flame
JF - Combustion and Flame
IS - 7
ER -