• Journal of the Korean Society of Combustion
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• v.18 no.4
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• pp.29-36
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• 2013

Numerical study was conducted to clarify effects of added $CO_2$ for the downstream interaction between $H_2$-air and CO-air premixed flames in counterflow configuration. The reaction mechanism adopted was Davis model which had been known to be well in agreement with reliable experimental data. The results showed that both lean and rich flammable limits were reduced. The most discernible difference between the two with and without having $CO_2$ addition into $H_2$-air and CO-air premixtures was two flammable islands for the former and one island for the latter at high strain flame conditions. Even a small amount of $H_2$, in which $H_2$-air premixed flame cannot be sustained by itself, participates in CO oxidation, thereby altering the CO-oxidation reaction path from the main reaction route $CO+O_2{\rightarrow}CO_2+O$ with a very long chemical time in CO-air flame to the (H, O, OH)-related reaction routes including $CO+OH{\rightarrow}CO_2+H$ with relatively short chemical times. This intrinsic nature alters flame stability maps appreciably. The results also showed that chemical effects of added $CO_2$ suppressed flame stabilization. Particularly this phenomenon was appreciable at flame conditions which lean and rich extinction boundary was merged. The detailed discussion of chemical effects of added $CO_2$ was addressed to the present downstream interaction.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.86-94
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• 1999

Measured shock wave effects were investigated by changing shock strength and position with particular emphasis on the stability limits of hydrogen-air jet flames. For this purpose, a supersonic nonpremixed, jet-like flame was stabilized along the axis of a Mach 2.5 wind tunnel, and wedges were mounted on the sidewall in order to interact oblique shock waves with the flame. This experiment was the first reacting flow experiment interacting with shock waves. Schilieren visualization pictures, wall static pressures, and flame stability limits were measured and compared to corresponding flames without shock-flame interaction. Substantial improvements in the flame stability limits were achieved by properly interacting the shock waves with the flameholding recirculation zone. The reason for the significant improvement in flame stability limits is believed to be the adverse pressure gradient caused by the shock, which can elongate the recirculation zone.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.65-71
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• 1999

An experimental study was carried out in order to investigate the effect of shock waves on the supersonic hydrogen-air jet flames stabilized in the Mach 2.5 model scramjet combustor. This experiment was the first reacting flow experiment interacting with shock waves. Two identical $10^{\cire}$ wedges were mounted on the diverging sidewalls of the combustor in order to produce oblique shock waves that interacted with the flame. Schlieren visualization pictures, wall static pressures, and combustion efficiency at two different air stagnation temperatures were measured and compared to corresponding flames without shock wave-flame interaction. It was observed that shock waves significantly altered the shape of supersonic jet flames, but had different effects on combustion efficiency depending on air temperatures. At the higher air stagnation temperature and higher fuel flow rates, combustion of efficiency showed a better result.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.907-914
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• 2005

Experiments at the Japan Microgravity Center (JAMIC) have investigated the interaction between diffusion flames and solid surfaces Placed neat flames The fuel for the flames was $C_{2} H_{4}$ The surrounding oxygen concentration was 35$\%$ with surrounding air temperatures of $T_{a}$ : 300K. Especially, the effect of wall temperature on soot deposition from a diffusion flame Placed near the wall has been studied by utilizing microgravity environment, which can attain very stable flame along the wall. Cylindrical burner with fuel injection was adopted to obtain two dimensional soot distributions by laser extinction method. In the experiment two different wall temperatures. $T_{w}$=300, 800 K, were selected as test conditions The results showed that the soot distribution between flame and burner wall was strong1y affected by the wall temperature and soot deposition increases with decrease in wall temperature. The comparison among the values lot two different wall temperatures suggests that the change in thermophoretic effect is the most dominant factor to give the change in soot deposition characteristics.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.87-92
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• 2005

Experiments at the Japan Microgravity Center(JAMIC) have investigated the interaction between diffusion flames and solid surfaces placed near flames. The fuel for the flames was $C_2H_4$. The surrounding oxygen concentration was 35% with temperatures of $T_a$=300. Especially, the effect of wall temperature on soot deposition from a diffusion flame placed near the wall has been studied by utilizing microgravity environment, which can attain very stable flame along the wall. Cylindrical burner with fuel injection was adopted to obtain two dimensional soot distributions by laser extinction method. In the experiment two different wall temperatures, $T_w$=300,800K, were selected as test conditions. The results showed that the soot distribution between flame and burner wall was strongly affected by the wall temperature and soot deposition increases with decrease in wall temperature. The comparison among the values for two different wall temperatures suggested that the change in thermophoretic effect is the most dominant factor to give the change in soot deposition characteristics.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.453-458
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• 2001

The stability of turbulent nonpremixed interacting flames is investigated in terms of nozzle configuration shapes which depend on the existence of the center nozzles. Six nozzle arrangements which are cross 4, 5, 8, 9, square 8 and circular 8 nozzles are used for the experiment. Those are arranged to see the effect of the center nozzle out of multi-nozzle. There are many parameters that affect flame stability in multi-nozzle flame such as nozzle separation distance, fuel flowrates and nozzle configuration, but the most important factor is the existence of nozzles in the center area from the nozzle arrangement. As the number of nozzle in the area is reduced, more air can be entrained into the center of flame base and then tag flame is formed. In the case of circular 8 nozzles, blowout flowrates are above 5.4 times compared with that of single equivalent area nozzle.

• Journal of Mechanical Science and Technology
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• v.18 no.5
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• pp.857-864
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• 2004

The change in the NO emission indices (EINO) in a two-dimensional plane has been investigated, which is due to the interaction between a vortex and methane-air flames established at different equivalence ratios, by solving the field equation. After solving the field equation, the spatial distribution of G-values is obtained. The NO emission index is calculated after applying the appropriate relation between the G-values and the NO production rate or the mass fraction of methane obtained from the library of freely propagating flames created from detailed simulations. When a vortex exists in a reacting flow field, in general EINO slightly increases, whereas ElNO is lowered in the vicinity of the vortex regardless of flow direction. A change in vortex size has negligible impact on EINO$\_$T/ but increasing the vortex strength slightly increases EINO$\_$T/ in the domain of this study.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.267-268
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• 2015

The multi-environment probability density function model has been applied to simulate the turbulent $CH_4/H_2$ flames under MILD conditions. The direct quadrature method of moments (DQMOM) has been adopted to solve the transport PDF equation due to its computational efficiency and robustness. The IEM model represents the micromixing process. The numerical results obtained in this study are precisely compared with experimental data in terms of unconditional means and conditional means for scalar field including temperature and species mass fraction.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.57-61
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• 2003

In the combustion modeling of non-premixed flames, the mixture fraction conserved scalar approach is widely utilized because reactants are mixed at the molecular level before burning and atomic elements are conserved in chemical reactions. In the mixture fraction approach, combustion process is simplified to a mixing problem and the interaction between chemistry and turbulence could be modelled by many sophisticated combustion models including the flamelet model and CMC. However, most of the mixture fraction approach is restricted to one mixture system. In this study, the flamelet model based on the two-feed system is extended to the multiple fuel-feeding systems by the two mixture fraction conserved scalar approach.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.600-609
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• 2001

WSGGM based low-resolution spectral model for calculating radiation transfer in combustion gases is applied to estimate self-absorption of radiation energy in one-dimensional opposed flow flames. Development of such a model is necessary in order to enable detailed chemistry-radiation interaction calculations including self-absorption. Database of band model parameters which can be applied to various one-dimensional opposed flow diffusion and partially premixed flames is created. For the validation of the model and database, low resolution spectral intensities at fuel exit side are calculated and compared with the results of a narrow band model with those based on the Curtis-Godson approximation. Good agreements have been found between them. The resulting radiation model is coupled to the OPPDIF code to calculate the self-absorption of radiant energy and compared with the results of an optically thin calculation and the results of a discrete ordinates method in conjunction with the statistical narrow band model. Significant self-absorption of radiation is found for the flames considered here particularly for the fuel side of the reacting zone. However, the self-absorption does not have significant effects on the flame structure in this case. Even in the case of the low velocity diffusion flame and the partially premixed flame of low equivalence ratio, the effects of self-absorption of radiation on the flame temperature and production of minor species are not significant.