“…This implies that oxy−fuel combustion significantly enhances flame stabilization because of a much higher burning velocity compared to air−fuel flames, as illustrated in Figure . The increase in oxidizer velocity decreases the yellowish luminosity from soot particles, flame length, and volume, because of the increase in turbulent intensity . These results are agree well with those of Wang et al 5 Flame images for four oxidizer injections at velocity V f = 60 m/s; (a) V o = 8.3, (b) V o = 18.0, (c) V o = 30.0, and (d) V o = 45.0 m/s.…”
Section: Resultssupporting
confidence: 89%
“…Ditaranto et al − showed that oxy−fuel combustion increases thermal efficiency and has potential for NO x emission reduction. They also showed that flame length and NO x emission are sensitive to air leaks into the combustion chamber.…”
Emission characteristics of the 0.03 MW oxy−fuel combustor have been experimentally investigated under
a wide operating range of velocity and quarl angle. To simulate the NO emission characteristics of industrial
oxy−fuel furnaces, we mixed 3% nitrogen by supplied oxygen with pure oxygen. When a quarl is not fitted,
the flame length decreased with increasing inlet fuel or oxidizer velocity, mainly because of the increase in
turbulent intensity. In the case of the high-speed injection of fuel or oxidizer without a quarl, NO emission
levels decrease because high-speed injection enhances the entrainment of product gas to the flame zone as
well as decreases the overall combustion residence time. When a quarl is fitted, the flame length increases
with expanding quarl angle because of the decrease in turbulent intensity. The NO emission level increases
with expanding quarl angle because both the entrainment of product gas is prevented and the overall combustion
residence time is increased with the installation of a quarl.
“…This implies that oxy−fuel combustion significantly enhances flame stabilization because of a much higher burning velocity compared to air−fuel flames, as illustrated in Figure . The increase in oxidizer velocity decreases the yellowish luminosity from soot particles, flame length, and volume, because of the increase in turbulent intensity . These results are agree well with those of Wang et al 5 Flame images for four oxidizer injections at velocity V f = 60 m/s; (a) V o = 8.3, (b) V o = 18.0, (c) V o = 30.0, and (d) V o = 45.0 m/s.…”
Section: Resultssupporting
confidence: 89%
“…Ditaranto et al − showed that oxy−fuel combustion increases thermal efficiency and has potential for NO x emission reduction. They also showed that flame length and NO x emission are sensitive to air leaks into the combustion chamber.…”
Emission characteristics of the 0.03 MW oxy−fuel combustor have been experimentally investigated under
a wide operating range of velocity and quarl angle. To simulate the NO emission characteristics of industrial
oxy−fuel furnaces, we mixed 3% nitrogen by supplied oxygen with pure oxygen. When a quarl is not fitted,
the flame length decreased with increasing inlet fuel or oxidizer velocity, mainly because of the increase in
turbulent intensity. In the case of the high-speed injection of fuel or oxidizer without a quarl, NO emission
levels decrease because high-speed injection enhances the entrainment of product gas to the flame zone as
well as decreases the overall combustion residence time. When a quarl is fitted, the flame length increases
with expanding quarl angle because of the decrease in turbulent intensity. The NO emission level increases
with expanding quarl angle because both the entrainment of product gas is prevented and the overall combustion
residence time is increased with the installation of a quarl.
“…The structures of turbulent diffusion flames have been described in a number of studies. 11,24,25 These same structures can be seen in these inverted coaxial turbulent diffusion flames. Close to the jet, exit laminar-like regions exist where the heat release has suppressed the turbulence.…”
Section: Resultssupporting
confidence: 66%
“…6 Whereas a majority of these studies cite combustion applications as a main reason for studying the flow field of coaxial jets, very few studies have actually investigated reacting flows. [7][8][9][10][11] The few studies of reacting coaxial jet flames have not quantified stoichiometric mixing lengths (L S ) or compared values of L S for reacting and nonreacting conditions. Both are done in the present work while systematically varying the parameters known to be important to coaxial jet mixing, namely r u and S.…”
Stoichiometric mixing lengths are obtained for coaxial jets with and without combustion in a rocket fuel injector configuration. With a center jet of oxidizer (oxygen or air) and a surrounding annular jet of hydrogen these flames are relatively short resulting in the mixing primarily occurring in the near field. This produces a different scaling than the far field analysis of a turbulent jet flame, where a fuel jet is injected into a coflow of oxidizer. Stoichiometric mixing lengths (LS), defined as the distance along the centerline where the stoichiometric condition occurs, were measured using Planar Laser Induced Fluorescence (PLIF). Acetone seeded into the center jet along with quantitative acetone PLIF allowed the direct measurement of the average and instantaneous mixture fraction fields for a range of velocity and density ratios. For hydrogen-oxygen and hydrogen-air coaxial jet flames, LS was measured from the OH radical field obtained using OH PLIF. Due to the inverse natural of these flames and since all cases were run fuel rich, OH forms thin layers near the stoichiometric contour. Using strained laminar flame calculations from Chemkin and correcting for absorption and quenching effects, the stoichiometric value of the OH signal was related to the peak signal. In nonreacting cases the use of a nondimensional momentum ratio collapses the nonreacting coaxial jet data. To account for the effect of heat release in reacting cases the equivalence principle of Tacina and Dahm is utilized to produce an equivalent outer gas density to create a new effective momentum ratio. This method is found to slightly under predict the effect of heat release for both hydrogen-oxygen and hydrogen-air turbulent coaxial jet flames.
“…An advantage of this technology is its potential to reduce nitric oxides (NO x ) emissions. Ditaranto et al [4][5][6] investigated NO x emissions from oxy-fuel flames without CO 2 dilution, as it is used in glass melting industry for instance. The authors observed that NO x emissions are especially influenced by air leaks and residual N 2 present in either natural gas or oxygen stream.…”
An experimental study on turbulent non-premixed jet flames is presented with focus on CO 2 -diluted oxy-fuel combustion using a coflow burner. Measurements of local temperatures and concentrations of the main species CO 2 , O 2 , CO, N 2 , CH 4 , H 2 O and H 2 were achieved using the simultaneous line-imaged Raman/Rayleigh laser diagnostics setup at Sandia National Laboratories. Two series of flames burning mixtures of methane and hydrogen were investigated. In the first series, the hydrogen molar fraction in the fuel was varied from 37 to 55 %, with a constant jet exit Reynolds number Re Fuel of 15,000. In the second series the jet exit Reynolds number was varied from 12,000 to 18,000, while keeping 55 % H 2 molar fraction in the fuel. Besides local temperatures and concentrations, the results revealed insights on the behaviour of localized extinction in the near-field. It was observed that the degree of extinction increased as the hydrogen content in fuel was decreased and as the jet Reynolds number was increased. Based on the distribution of the temperature, a fully burning probability index able to quantify the degree of extinction along the streamwise coordinate was defined and applied to the present flame measurements. A comparison of measured conditional mean of mass fractions and laminar flame calculations underlined the significant level of differential diffusion in the near-field that tended to decrease farther downstream. The results also showed high local CO levels induced by the high content of CO 2 in the oxidizer and flame products. A shift of maximum flame temperature was observed toward the rich side of the mixture fraction space, most likely as a consequence of reduced heat release in the presence of product dissociation. Main characteristics of laser Raman scattering measurements in CO 2 -diluted oxy-fuel conditions compared to air-diluted conditions are also highlighted. Most data, including scalar fluctuations and conditional statistics are available upon request.
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