A numerical study of the diffusive-thermal instability of opposed nonpremixed tubular flames

Bak, Hyun Su; Lee, Su Ryong; Chen, Jacqueline H.; Yoo, Chun Sang

doi:10.1016/j.combustflame.2015.09.019

Cited by 8 publications

(3 citation statements)

References 36 publications

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“…Here, S L is evaluated based on temperature and species information upstream of the flamebase to incorporate the effect of autoignition. For this purpose, S e is obtained through the density-weight displacement speed, S * d , which has been used to evaluate the propagation speed of reaction fronts in many previous studies [13,14,[58][59][60][61][62][63][64]. S * d is defined by:…”

Section: Effect Of Hydrogen On the Lifted Flame Stabilizationmentioning

confidence: 99%

Differential diffusion effect on the stabilization characteristics of autoignited laminar lifted methane/hydrogen jet flames in heated coflow air

Jung

Kim

et al. 2018

Combustion and Flame

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The characteristics of autoignited laminar lifted methane/hydrogen jet flames in heated coflow air are numerically investigated using laminarSMOKE code with a 57-species detailed methane/air chemical kinetic mechanism. Detailed numerical simulations are performed for various fuel jet velocities, U 0 , with different hydrogen ratio of the fuel jet, R H , and the inlet temperature, T 0 . Based on the flame characteristics, the autoignited laminar lifted jet flames can be categorized into three regimes of combustion mode: the tribrachial edge flame regime, the Moderate or Intense Low-oxygen Dilution (MILD) combustion regime, and the transition regime in between. Under relatively low temperature and high hydrogen ratio (LTHH) conditions, an unusual decreasing liftoff height, H L , behavior with increasing U 0 is observed, qualitatively similar to those of previous experimental observations. From additional simulations with modified hydrogen mass diffusivity, it is substantiated that the unusual decreasing H L behavior is primarily attributed to the high diffusive nature of hydrogen molecules. The species transport budget, autoignition index, and displacement speed analyses verify that the autoignited lifted jet flames are stabilized by autoignition-assisted flame propagation or autoignition depending on the combustion regime. Chemical explosive mode analysis (CEMA) identifies important variables and reaction steps for the MILD 1 combustion and tribrachial edge flame regimes.

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Section: Effect Of Hydrogen On the Lifted Flame Stabilizationmentioning

confidence: 99%

Differential diffusion effect on the stabilization characteristics of autoignited laminar lifted methane/hydrogen jet flames in heated coflow air

Jung

Kim

et al. 2018

Combustion and Flame

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“…where Y k is the mass fraction, V k,j the diffusion velocity in the j−direction, ω k the net production rate of species k, and ρ u is the density of the unburnt mixture. S * d has been widely used to estimate the propagation speeds of reaction fronts [3,4,42,[50][51][52]. Here, we adopt OH for the evaluation of S shows that temperature increases from T 0 (=980 K) at the upstream of the flamebase.…”

Section: Stabilization Mechanismsmentioning

confidence: 99%

A numerical study of the pyrolysis effect on autoignited laminar lifted dimethyl ether jet flames in heated coflow air

Jung

Kang

et al. 2019

Combustion and Flame

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The liftoff, autoignition, and stabilization characteristics of autoignited laminar lifted dimethyl ether (DME) jet flames in heated coflow air are numerically investigated by varying the fuel jet velocity, U 0. The detailed numerical simulations are performed using the laminarSMOKE code with a 55-species detailed kinetic mechanism of DME oxidation. An unusual U-shaped liftoff height, H L , behavior under MILD combustion condition is observed from the simulations, which is qualitatively consistent with previous experimental results. From additional numerical simulations with modified mass diffusivity of hydrogen, it is verified that the decreasing H L trend of the lifted flames under relatively-low U 0 conditions is mainly attributed to the fast diffusion of hydrogen generated from the DME pyrolysis. The species transport and displacement speed analyses verify that the differential diffusion effect renders the lifted flames to be leaner at the center of the jet, ultimately leading to the change of their stabilization mechanism from the autoignition to the autoignition-assisted flame propagation mode with increasing U 0. The chemical explosive mode analysis (CEMA) identifies important variables and reactions contributing to the autoignition of the DME jet flames, through which the fast diffusion rates of small species are found to cause the deviation of 2-D autoignition characteristics from that of 0-D homogeneous ignition. The effects of DME pyrolysis on the characteristics of the autoignited laminar DME jet flames are further investigated by varying the fuel tube length, L res. H L shows a non-monotonic behavior with increasing L res because the flame structure changes from a MILD combustion to a tribrachial edge flame and to an 1 attached flame while the stabilization mechanism also changes from the autoignition to the autoignition-assisted flame propagation mode as the degree of the DME pyrolysis increases.

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“…Non-rotational tubular flame has been investigated numerically and experimentally [6][7][8][9][10][11][12][13][14], but only experimental studies have been investigated the structure and stability limits of rotating tubular flames. Shimokuri and Ishizuka [15] proposed a technique to stabilize a flame in a high-velocity stream with the use of a tubular flame.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of non-premixed and premixed rotational tubular flame: a study of flame structure and instability

Bordbar

Motaghian

Pasdarshahri

2019

J Braz. Soc. Mech. Sci. Eng.

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Tubular flames are considered due to their advantages in the geometry of the flame. The major importance of tubular flame which makes it different from other flames is its uniform temperature distribution. Therefore, it reduces the possibility of the formation of thermal fluctuations and hot spots along the furnaces. In this paper, high-speed, non-premixed and premixed tubular flames are numerically investigated using computational fluid dynamics under various operational conditions. Methane/air and CO 2-diluted methane/oxygen combustions are considered in both non-premixed and premixed modes. k − SST model, eddy dissipation concept combustion model, and P1 radiation model have been used as numerical models. Numerical results are validated against available experimental measurements in the non-premixed tubular flame using DRM22 kinetic mechanism for methane/air combustions and GRI-Mech 3.0 for methane/oxygen mixtures. The structure of the tubular flame in the combustion chamber and stability limits of tubular flame in terms of operating conditions have been studied in the present paper. Results show that premixed tubular flames establish more uniform radial temperature distribution and wider stable flame operating conditions. In addition, diluted methane/oxygen tubular flames have been shown broader stable condition limits than methane/air flames.

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A numerical study of the diffusive-thermal instability of opposed nonpremixed tubular flames

Cited by 8 publications

References 36 publications

Differential diffusion effect on the stabilization characteristics of autoignited laminar lifted methane/hydrogen jet flames in heated coflow air

Differential diffusion effect on the stabilization characteristics of autoignited laminar lifted methane/hydrogen jet flames in heated coflow air

A numerical study of the pyrolysis effect on autoignited laminar lifted dimethyl ether jet flames in heated coflow air

Numerical investigation of non-premixed and premixed rotational tubular flame: a study of flame structure and instability

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