Nitrogen oxides emissions in turbulent hydrogen jet non-premixed flames: Effects of coaxial air and flame radiation

Kim, Seung-Han; Yoon, Youngbin; Jeung, In‐Seuck

doi:10.1016/s0082-0784(00)80244-1

Cited by 37 publications

(32 citation statements)

References 17 publications

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“…Kim et al [8] experimentally confirmed this relationship between normalized flame lengths and U A /U F . Figure 4 represents the comparison of measured and predicted flame lengths.…”

Section: Flame Length and Einoxmentioning

confidence: 76%

“…To examine the effects of coaxial air on NOx for mation, we have performed a numerical analysis for various cases of experiments [8]. The inner diameter and the lip thickness of the fuel nozzle are 3.0 and 0.5mm, respectively.…”

Section: Flame Length and Einoxmentioning

confidence: 99%

“…Driscoll et al [2,3] demonstrated that the effect of coaxial air, which increases mixture homogeneity and shortens the flame length, induces lower NOx emission index than that in the simple jet flames with no coaxial air. More recently, in order to improve the understanding of the physical mechanisms associated with EINOx scaling in coaxial air flames, Kim et al [8] conducted experiments by varying coaxial air velocity with fixed fuel velocity, and by varying fuel velocity with fixed coaxial air. They found that unlike simple jet flames, EINOx normalized by flame residence time in coaxial air flames is not simply correlated with flame residence time, but rather can be scaled with global strain rate successfully.…”

Section: Introductionmentioning

confidence: 99%

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NOx emission characteristics in turbulent hydrogen jet flames with coaxial air

2009

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The characteristics of NOx emissions in pure hydrogen nonpremixed jet flames with coaxial air are analyzed numerically for a wide range of coaxial air conditions. Among the models tested in simple nonpremixed jet flame, the one-half power scaling law could be reproduced only by the Model C using the HO 2 /H 2 O 2 reaction, implying the importance of chemical nonequilibrium effect. The flame length is reduced significantly by augmenting coaxial air, and could be represented as a function of the ratio of coaxial air to fuel velocity. Predicted EINOx scaling showed a good concordance with experimental data, and the overall one-half power scaling was observed in coaxial flames with Model C when flame residence time was defined with flame volume instead of a cubic of the flame length. Different level of oxygen mass fraction at the stoichiometric surface was observed as coaxial air was increased. These different levels imply that the coaxial air strengthens the nonequilibrium effect.

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“…Kim et al [8] experimentally confirmed this relationship between normalized flame lengths and U A /U F . Figure 4 represents the comparison of measured and predicted flame lengths.…”

Section: Flame Length and Einoxmentioning

confidence: 76%

Section: Flame Length and Einoxmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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NOx emission characteristics in turbulent hydrogen jet flames with coaxial air

2009

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“…These phenomena should reflect the enhancement of mixing and flame stretch (6) . In the case of D 1 = 95 mm, the size of the recirculation vortex should be smaller than the other cases, owing to the smaller space between the flames and the wall.…”

Section: Characteristics Of Nox Emissionmentioning

confidence: 98%

An Experimental Study of Flame Characteristics of Jet Diffusion Flames in Cylindrical Furnaces (1st Report, Effect of Inner Diameter of Furnace on NOx Emission Properties)

Noda

Inohae

Nakano

et al. 2007

JEE

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The combination of a burner and a combustion chamber is an important factor controlling flame characteristics. However, to our knowledge, this factor has yet to be investigated systematically. In the present study, coaxial jet diffusion flames in cylindrical combustion chambers have been studied in terms of inner diameters of the combustion chambers, global equivalence ratios, and turbulence in airflow. A fuel nozzle is composed of a stainless steel tube having an inner diameter (i.d.) of 2 mm with a coaxial pilot burner of 3.19 mm i.d., surrounded by two air coaxial tubes of 12 mm i.d. and 30 mm i.d., respectively. The inner and outer air tubes are for higher and lower airflows, respectively, and the turbulence in the airflow is changed by the velocity difference. The main fuel is propane. Hydrogen is used for the pilot flame, with a volumetric fuel ratio of 0.3. Each wall of the combustion chamber is made of a heat-resistant glass Pyrex tube so that each flame can be visualized. The inner diameter of the furnace is varied in order to investigate the effect of furnace size on the flame characteristics. The increase in the diameter of the combustion chamber has been found to enhance the exhaust gas self-recirculation, because the NOx emission decreases. The increase in turbulence in the airflow strengthens the entrainment of the exhaust gas transported upstream by the recirculation vortex. The increase in the global equivalence ratio from 0.2 to 0.8 in the present study decreases the oxygen concentration of the exhaust gas and leads to diluted combustion through the exhaust gas self-recirculation. A proper combination of these factors has been found to yield a low NOx combustion.

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“…The EINOx scaling takes flame volume and fuel flow rate in to consideration, and this means that the EINOx is proportional to the residence time of the fuel, which is passing through the flame. Driscoll et al (4) and Kim et al (5) incorporated the flame stretch effect on NOx emission in confined flames with a co-flow air stream in to a scaling law. These investigations have not only generated scaling law but have also provided insights and understanding with respect to the flame structure of non-premixed combustion.…”

Section: Introductionmentioning

confidence: 99%

NOx Reduction of Non-Premixed Flames by Combination of Burner and Furnaces

Somarathne

Parwatha

Oguri

et al. 2013

JEE

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This study proposes an idea of NOx reduction and high efficiency combustion by combination of burner and furnace. This is basically attributed to the use of entrainment of burnt gases to flame in furnace. The entrainment of burnt gases leads the dilution of flame and the recovery of heat to be exhausted. The phenomena are strongly related to the geometry of burner and furnace. The temperature, concentration, and flow field characteristics were investigated for piloted propane non-premixed flames in the cylindrical furnaces in terms of NOx emission. The effects of the furnace inner diameter, D 1 , air inlet velocity difference, ∆U a , and global equivalence ratio,φ, on NOx emission were investigated.Moreover, two kinds of materials: Pyrex glass and stainless steel were used as the furnace wall to evaluate the radiation effect through the comparison of the flame characteristics. The emission index of NOx, EINOx, decreases roughly with the increase of above parameters. This decrease is observed to be a consequence of dilution by the burnt gases and flame stretch. The dilution is attributed to the recirculation structure, which is formed at the bottom of the furnace. The flame stretch is related to the velocity difference, which is introduced by multiple air inlets. The EINOx of confined non-premixed flame is scaled by the parameter D 1 U F ∆U a , which is proportional to Re,cDa -1 . Here, U F is the fuel velocity, Re,c is the furnace Reynolds number reflecting the turbulence in the furnace, and Da is the Damköhler number reflecting the flame stretch. The parameter D 1 U F ∆U a is related linearly to the volume flow rate entrained in to the flame. Thus, this study verified that the EINOx of confined non-premixed flame is dominated primarily from the entrainment of burnt gases by the recirculation vortex and secondarily by the turbulence at the flame boundary, which is generated by the air velocity difference. In addition, it is found that under present experimental conditions, the radiation effect on the EINOx is small and constant with respect to the parameters. Thus, this idea has a potential for practical applications.

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Nitrogen oxides emissions in turbulent hydrogen jet non-premixed flames: Effects of coaxial air and flame radiation

Cited by 37 publications

References 17 publications

NOx emission characteristics in turbulent hydrogen jet flames with coaxial air

NOx emission characteristics in turbulent hydrogen jet flames with coaxial air

An Experimental Study of Flame Characteristics of Jet Diffusion Flames in Cylindrical Furnaces (1st Report, Effect of Inner Diameter of Furnace on NOx Emission Properties)

NOx Reduction of Non-Premixed Flames by Combination of Burner and Furnaces

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