Characteristics of backward-inclined non-premixed jet flames in crossflow

• Published in: Experimental thermal and fluid science Vol. 98; pp. 429 - 444
• Main Authors: Mosiria, Dickson Bwana, Huang, Rong Fung, Hsu, Ching Min
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-11-2018
• Subjects: Diffusion flame; Jet flame in crossflow; Recirculation zone; Shear layer vortices; Recirculation zone; Shear layer vortices; Diffusion flame; Jet flame in crossflow
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2018.06.029

•Jet inclination angle changed flow modes and therefore changed flame behaviors.•Shear-layer vortices and recirculation bubble dominated flame behaviors.•Three flame modes: crossflow dominated, transitional, and jet dominated.•Down-wash recirculation flames appeared at inclination angle smaller than 40 deg.•Temperature profiles presented characteristics in different flame modes.
The characteristics of backward-inclined non-premixed jet flames in a uniform crossflow were studied in a wind tunnel. Time-averaged photography techniques were used to study flame behavior. The flow field was captured by short exposure photography and Mie-scattering techniques. Flame temperatures were probed with a fine-wire R-type thermocouple. In the domain of jet-to-crossflow momentum flux ratio R and backward-inclination angle θ, the flames were categorized into three characteristic modes. The first mode consisted of crossflow dominated flames characterized by a down-wash recirculation flame in the wake of the burner tube. The second mode consisted of transitional flames characterized by a yellowish recirculation flame and a tail flame. The third mode consisted of jet dominated flames characterized by a blue flame base and an absence of the down-wash flame. The down-wash recirculation flames were observed for a backward inclination angle of θ < 40°. The ability of the flames to resist blow off when increasing the jet-to-crossflow momentum flux ratio decreased as θ increased. Coherent vortices were observed on the seeded fuel jet, whose type was dependent on R and θ. In the upstream region, the fuel appeared above the flame. However, in the downstream region, the fuel became engulfed within the flame. For a fixed θ, the Strouhal number of the upwind shear layer vortices on the fuel jet was observed to decrease asymptotically as R increased. In the near-field at x/d ≈ 5, the crossflow dominated flames presented temperature profiles characterized by a broad dual-hump peak profile in the symmetry plane, while in the near-field at x/d ≈ 5, the jet dominated flames presented a single peak profile in the symmetry plane.