Stabilization criteria of laminar lifted propane flames and their transition to turbulent lifted flames under extended pressures

• Published in: Fuel (Guildford) Vol. 343; p. 127960
• Main Authors: Hwang, Gyu Jin, Jeon, Dong Seok, Kim, Nam Il
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2023
• Subjects: Edge flame speed; Effective fuel concentration gradient; Effective Schmidt number; Flame stabilization; Lifted flame; Effective fuel concentration gradient; Edge flame speed; Lifted flame; Flame stabilization; Effective Schmidt number
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2023.127960

•Laminar lifted propane flames were examined under extended pressures.•A triangular stabilization regime of the laminar lifted flames was confirmed.•Edge flame speed (EFS) was related to effective fuel concentration gradient (EFCG).•The existence of the minimum EFS at the maximum EFCG was clarified.•The structural transition from laminar to turbulent lifted flames was investigated. Recently, the mechanism of a laminar lifted flame (LLF) was clearly explained using an effective Schmidt number. It was found that a stable LLF can be formed within a triangular stabilization regime (TSR) in the domain of normalized lift-off height and Reynolds number. However, the experimental pressure range in the previous study was limited to three-times (1–3 bar) because there was an early transition to turbulent flow at elevated pressures. This study examined the effects of pressure on the LLF characteristics of propane, within an extended pressure range of 12.5-times (0.2–2.5 bar) with larger fuel tubes. This allowed more precise and abundant experimental results to be obtained for flame structures, and the general TSR for all LLFs was confirmed. In addition, variations in the effective Schmidt numbers and effective diffusivities were estimated for extended pressures, and the correlation between the fuel jet velocities and the lift-off heights was explained. Conclusively, a more general relationship between the edge flame speed (EFS) and the effective fuel concentration gradient (EFCG) was obtained under extended pressures. The existence of a minimum EFS at the maximum EFCG was confirmed. Furthermore, the non-monotonic variation in the lift-off height was explained, and the variations in the flame structure during the transition from an LLF to a turbulent lifted flame were investigated in more detail.