• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.242-250
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• 2006

Detailed structures of the counterflow flames formed for different inlet fluid temperatures and different amount of additives are studied numerically. The detailed chemical reactions are modeled by using the CHEMKIN-II code. The discrete ordinates method and the narrow band based WSGGM with a gray gas regrouping technique (WSGGM-RG) are applied for modeling the radiative transfer through non-homogeneous and non-isothermal combustion gas mixtures generated by the counterflow flames. The results compared with those obtained by using the SNB model show that the WSGGM-RG is very successful in modeling the counterflow flames with non-gray gas mixture. The numerical results also show that the addition of $CO_2\;or\;H_2O$ to the oxidant lowers the peak temperature and the NO concentration in flame. But preheat of fuel or oxidant raises the flame temperature and the NO production rates. $O_2$ enrichment also causes to raise the temperature distribution and the NO production in flame. And it is found that the $O_2$ enrichment and the fuel preheat were the major parameters in affecting the flame width.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.1
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• pp.108-116
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• 1998

In this paper it is investigated the roles of key elementary reactions for NO formation in methane-air one-dimensional premixed flame and counterflow diffusion flame, which were studied numerically by using NO kinetics and $C_{2}$ -chemistry complied by Miller and Bowman. The spatial distributions of the reaction rates of 9 main elementary reactions directly related to NO formation and destruction were calculated. Integration of the rates of all reactions in the NO formation across the flame yields the quantitative reaction path diagram, which shows clearly relative importance of each reaction path in NO formation and how it changes with the type and parameters of the flame. The results show that the thermal and Fenimore mechanisms are dominant respectively for learn and rich premixed flames, and the latter is dominant for diffusion flames. In addition, it was found that the HCN recycle route is important for diffusion flame, and that the routes of mutual transformation between NO and NO$^{2}$, and between NO and HNO do not contribute to the net NO formation.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.8
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• pp.853-862
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• 2006

The present study is numerically investigated the flame structure of non-premixed counterflow jet flames using the laminar flamelet model Detailed flame structures with the fuel composition of 40% CO, 30% $H_2$. 30% $N_2$ and an oxidizer composition of 79% $N_2$ and 21% $O_2$ in a non-premixed counterflow flame are studied numerically. This study is aimed to investigate the effects of axial velocity gradient and combustion atmosphere pressure on flame structure. The results show that the role of axial velocity gradient on combustion processes is globally opposite to that of combustion atmosphere pressure. That is, chemical nonequilibrium effects become dominant with increasing axial velocity gradient, but are suppressed with increasing ambient pressure. Also, the flame strength is globally weakened by the increase of axial velocity gradient but is augmented by the increase of ambient pressure. However, flame extinction is described better on the basis of only chemical reaction and in this study axial velocity gradient and ambient pressure play a similar role conceptually such that the increase of axial velocity gradient and ambient pressure cause flame not to be extinguished and extend the extinction limit, respectively. Consequently it is suggested that a combustion process like flame extinction is mainly influenced by the competition between the radical formation reaction and the third-body recombination reaction.

• Journal of the Korean Society of Combustion
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• v.9 no.4
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• pp.22-27
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• 2004

Lean premix combustion is a best method in low $NO_x$ gas turbine combustor and we must know the characteristics of NO emission in high temperature and pressure condition in premix flame. Numerical analysis was performed to investigate the NO emission characteristics by adopting a counterflow as a model problem using detailed chemical kinetics. Methane $(CH_4)$ was used as a test fuel which is the main fuel of natural gas. The tested parameters were stretch rate, equivalence ratio, initial temperature, and pressure in premix flame. Results showed that NO emission was high in low stretch rate, near stoichiometric equivalence ratio, high initial temperature, and high pressure. Also, the pressure effect was sensitive in high temperature condition.

• Journal of the Korean Society of Combustion
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• v.4 no.2
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• pp.97-108
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• 1999

This numerical study was to investigate the effect of $CO_2$ addition on the structures and NOx formation characteristics in $CH_4$ counterflow diffusion flame. The importance of radiation effect was identified and $CO_2$ addition effect was investigated in terms of thermal and chemical reaction effect. Also the causes of NOx reduction were clarified by separation method of each formation mechanisms. The results were as follows : The radiation effect was intensified by $CO_2$ addition. Thermal effect mainly contributed to the changes in flame structure and the amount of NO formation but the chemical reaction effect also cannot be neglected. The reduction of thermal NO was dominant with respect to reduction rate, but that of prompt NO was dominant with respect to total amount.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.8-16
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• 2001

Various technologies for the reduction of atmospheric pollution have been developed. One of which is to inject fine-water droplets directly on the flame. This way decreases the formation of thermal NOx due to the temperature drop during evaporation of droplets. There is another effect of reducing prompt NOx, which is resulted from delay of response time and the flow of droplets. In this experiment, it has been investigated the effects of changes of water droplets size and flow rate on temperature and formations of NOx at the counterflow diffusion flame.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.10a
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• pp.88-89
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• 2011

The study on synthesis of carbon nanomaterials by H2 mixing in counterflow methane diffusion flames has been experimentally conducted. We have also investigated on effect of catalyst and temperature in flame. The counterflow flame was formed by many kind of gas (fuel side using $CH_4-H_2-N_2$ and oxidizer side $N_2-O_2$) and nitrogen shields discharge on each other side to cut off oxidizer of the atmosphere. Ferrocene was used as a metal catalyst for CNTs synthesis. substrate was used to deposit carbon nanomaterials and these were analyzed by FE-SEM. We could find that carbon nanotubes and many kind of carbon nano materials were formed in Cu wire substrate, through this experiment.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.93-101
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• 2003

The extinction of unsteady diffusion flame was experimentally studied in an opposing jet counterflow burner using diluted methane. The stabilized flame was perturbed by linearly varying velocity change that was generated by pistons installed on both sides of the air and fuel stream. As the results, the extinction of unsteady flame is dependent not only on the history of unsteadiness, but also on the initial condition. We found that there are several unsteady effects on the flame extinction. First, the extinction strain rates of unsteady cases are extended well beyond steady state extinction limits. Second, as the slope of the strain rate change increases, the unsteady extinction strain rate becomes larger. Third, the extension of unsteady extinction strain rate becomes smaller as the initial strain rate increases. We also found that the extension of the extinction limit mainly results from the unsteady response of the reaction zone because there is no retardation effect of a mixing layer for our experimental condition.

• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.107-111
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• 2002

A near extinction nonpremixed counterflow flame of 19% methane diluted by 81% nitrogen by volume and undiluted air at a low global strain rate, 20 s-1, was computed. Investigations were focused on effects of the duct thickness and velocity boundary conditions on the flame structure in normal and zero gravity conditions. The results showed that, under normal gravity conditions, the effects of the duct thickness and velocity boundary conditions were significant by shifting the flame position, but negligible in zero gravity. The differences in flame structure were caused by buoyancy, and hence should be considered in the measurements in normal gravity.

• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.112-117
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• 2002

The effects of shield gas on the structure of methane-air nonpremixed counterflow flames were numerically investigated. The near extinction flame of a low global strain rate 20 $s^{-1}$ of 19% methane diluted by 81% nitrogen by volume and undiluted air was computed. The flame shape, centerline temperature and axial velocity profiles were compared for different velocity of the shield gas and with and without the shield gas. The effects of the velocity of the shield gas were negligible for $V_{S}/V_{F}{\leq}2$ in normal gravity. Under normal gravity conditions, the flame shape and its position with the shield gas were different from those of the flame without the shield gas, whereas no discernible effects of the shield gas along the centerline were observed in zero gravity.