Flame Entrainments Induced by a Turbulent Reacting Jet Using High-Temperature and Oxygen-Deficient Oxidizers

• Published in: Energy & fuels Vol. 19; no. 4; pp. 1473 - 1483
• Main Authors: Yang, Weihong, Blasiak, Wlodzimierz
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.07.2005
• Subjects: air; Applied sciences; combustion; Combustion of gaseous fuels; Combustion. Flame; diffusion flames; Energy; Energy. Thermal use of fuels; Exact sciences and technology; flow structure; furnace; heat release; lpg flame; momentum flux; oxidation; regenerative burner; Theoretical studies. Data and constants. Metering; Turbulent flame; Flow rate; Turbulent flow; Jet flow; Flame temperature; Buoyancy; Measurement result; Temperature effect; High temperature; Heat liberation; Numerical analysis; Length; Concentration effect; Oxygen effect; Comparative study; Low temperature
• ISSN: 0887-0624; 1520-5029; 1520-5029
• DOI: 10.1021/ef049763o

The entrainments of a turbulent jet in co-flow under high-temperature and oxygen-deficient oxidizers have been numerically and theoretical studied. By describing the chemical flame reaction, the entrainment induced by a turbulent reacting jet flame is calculated along the entire chemical flame length by mean of a flame entrainment ratio. The results in the near field of a reacting jet are verified by comparison with the results of published measurements. The effects of preheat temperature, the oxygen concentration of the oxidizer, the heat release, and buoyancy on the entrainment rate are investigated. The following results were obtained:  (1) The uniformity of the heat release in reacting jets has a strong effect on the flame entrainment:  the more uniform the heat release, the greater the entrainment. The effect of heat release reduces the entrainment in the near field of the reacting jets with the same factor of the characteristic ratio, which is r = (T f/T o)0.5. (2) The entrainment increases as the oxygen concentration is decreased. Furthermore, the entrainment is independent of the fuel flow rate and the preheat temperature of the oxidizer for the investigated temperature range (1073−1573 K). (3) The effect of the oxygen concentration and preheat temperature of the oxidizer on buoyancy was examined. A correction Richardson coordinate, which includes the effect of the oxygen concentration (stoichiometric ratio), was derived to describe the local influence of buoyancy force along the chemical flame length under the high-temperature and oxygen-deficient oxidizer conditions. It can be concluded that the buoyancy force increases with the reduction of the oxygen concentration in the oxidizer. (4) The global behavior of the entrainment was revealed. The entrainment of jet flames can be identified as two regimes:  (i) the near field, where the entrainment coefficient is positive, and (ii) the far field, where the entrainment coefficient is negative. Corrections for the entrainment rates were derived in terms of a Froude number (Fr) for the momentum−buoyancy transition jet flame under the high-temperature and low-oxygen-concentration oxidizer conditions. Furthermore, the maximum entrainments along the flame length are estimated.