• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.11
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• pp.1407-1416
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• 2004

A two-dimensional direct numerical simulation was performed to investigate the flame structure of CH$_4$/$N_2$-Air counterflow nonpremixed flame interacting with a single vortex. The detailed transport properties and a modified 16-step augmented reduced mechanism based on Miller and Bowman's detailed chemistry were adopted in this computation. The results showed that an initially flat stagnation plane, on which an axial velocity was zero, was deformed into a complex-shaped plane, and an initial stagnation point was moved far away from a vortex head when the counterflow field was perturbed by the vortex. It was noted that the movement of stagnation point could alter the species transport mechanism to the flame surface. It was also identified that the altered species transport mechanism affected the distributions of the mixture fraction and the scalar dissipation rate.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.192-197
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• 2004

Recently, fluidic thrust vectoring methods have been preferably employed to control the movement of propulsive systems due to relatively simpler design and lower cost than mechanical thrust vectoring methods. For An application of the thrust vectoring to flight bodies, it is necessary to understand very complicated exhaust flows which are often subject to shock waves and boundary layer separation. But researches for the thrust vector control using counterflow have been few. In the present study, experiments have been performed to investigate the characteristics of supersonic jets controlled by a thrust vectoring method using counterflow. The primary jet is expanded through a two-dimensional primary nozzle shrouded by collars, and is deflected by the suction of the air near nozzle into an upper slot placed between the primary nozzle and the upper collar. A shadowgraph method is used to visualize the supersonic jet flowfields. Primary nozzle pressure ratios and suction nozzle pressure ratios are varied from 3.0 to 5.0, and from 0.2 to 1.0 respectively. The present experimental results showed that, for a given primary nozzle pressure ratio, a decrease in the suction nozzle pressure ratio produced an increased thrust vector angle. As the suction nozzle pressure ratios were increased and decreased, the hysteresis of the thrust vectoring was observed through the wall pressure distributions

• Journal of the Korean Society of Safety
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• v.25 no.2
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• pp.12-17
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• 2010

Numerical simulations were performed for the prediction of the flame structure during the interaction between hydrogen and hydrocarbon flames. A counterflow flow geometry was introduced to establish the interacting two flames. Methane was used as a representative hydrocarbon fuel in this study. A well-known numerical code for the counterflow flame, OPPDIF, was used for the simulations. The detailed chemistry was adopted to predict the flame structure reasonably. The interaction of two one-dimensional premixed flames established in counterflow burner was investigated with the global strain rate and velocity ratio. It was found that the maximum temperature located near the methane flame surface while the heat release rate of methane was lower than hydrogen flame. The flame thickness become narrow with increasing the velocity ratio while the global strain rate was fixed. The local strain rate and heat release rate at the methane flame surface were correlated with the global strain rate, while those at the hydrogen flame were not correlated with the global strain rate. However, the maximum temperature of the interacting flames was correlated with the global strain rate.

• 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 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.

• International Journal of Safety
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• v.2 no.1
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• pp.12-16
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• 2003

In Part 1, the flame structure of the counterflow nonpremixed flames computed by using Fire Dynamics Simulator was compared with that of OPPDIF for different concentrations of methane in the fuel stream. In this study, comparisons were made for the global strain rate that is an important parameter for diffusion flames for further evaluation of FDS. At each of the three fuel concentrations, $20% CH_4＋ 80% N_2, 50% CH_4 ＋ 50% N_2, 90% CH_4 ＋ 10% N_2$ in the fuel stream, the temperature and axial velocity profiles were investigated for the global strain rate in the range from 20 to $100s^{-1}$. Changes in flame thickness and radius were also compared with OPPDIF. There was good agreement in the temperature and axial velocity profiles between the axisymmetric simulations and the one-dimensional computations except for the regions where the flame temperature reach its peak and the axial velocity rapidly changes. The simulations of the axisymmetric flames with FDS showed that the flame thickness decreases and the flame radius increases with increasing global strain rate.

• 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.

• Journal of Mechanical Science and Technology
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• v.16 no.2
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• pp.262-269
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• 2002

The effects of velocity boundary conditions on the structure of methane-air nonpremixed counterflow flames were investigated by two-dimensional numerical simulation. Two low global strain rates, 12 s$\^$-1/ and 20 s$\^$-1/, were considered for comparison with measurements. Buoyancy was conformed to have strong effects on the flame structure at a low global strain rate. It was shown that the location where a top hat velocity profile was imposed is sensitive to the flame structure, and that the computed temperature along the centerline agrees well with the measurements when plug flow was imposed at the inner surface of the screen nearest the duct exit.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.3
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• pp.378-386
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• 2009

The effect of fuel mixing on soot structure with methane, ethane, and propane to ethylene-base counterflow diffusion flames has been investigated by measuring the volume fraction, number density, and particle size of soot by adopting the light extinction/scattering techniques. The experimental result showed that the mixing of ethane and propane in ethylene diffusion flame increased soot volume fraction while the mixing of methane decreased. As compare to the ethylene-base flame, the diameters of soot particles for mixture flames are slightly smaller. While the soot number densities for the mixture flames are much higher. Thus, the increase in the soot volume fraction can be attributed to the appreciably increased soot number density by the fuel mixing.