• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.11a
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• pp.23-29
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• 1999

Experimental studies are conducted to investigate the flame stability and the thermal/fuel NOx formation characteristics of the low calorific value (LCV) coal derived gas fuel. Synthetic LCV fuel gas is produced by mixing carbon monoxide, hydrogen, nitrogen and ammonia on the basis that the thermal input of the syngas fuel into a burner is identical to that of natural gas. The syngas mixture is fed to and burnt with air on flat flame burner. With the variation of the equivalence ratio for specific syngas fuel, flame behaviors are observed to identify the flame instability due to blow-off or flashback and to define stable combustion range. Measurements of NOx content in combustion gas are made for comparing thermal and fuel NOx from the LCV syngas combustion with those of the natural gas one. In addition, the nitrogen dilution of the LCV syngas is preliminarily attempted as a NOx reduction technique, and its effects on thermal and fuel NOx production are discussed.

• Journal of the Korean Society of Combustion
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• v.21 no.1
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• pp.8-17
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• 2016

Downstream interactions between lean premixed flames with mutually different fuels of syngas and $CH_4$ have been numerically investigated particularly on and near lean extinction limits. The interaction characteristics between lean premixed (50% $H_2$ + 50% CO)-air and $CH_4$-air flames were shown to be quite different from those between the same hydrocarbon flames. The lean extinction boundaries were of slanted shape, thereby implying strong interactions. The weaker flames had negative flame speeds on the upper extinction boundaries, whereas the weaker flame speeds on the lower extinction boundaries were both negative and positive. The results also showed that the flame interaction characteristics did not follow the general tendency with the dependency of Lewis number in downstream interactions between the same hydrocarbon flames. Importance of chemical interaction in flame characteristics is discussed in the downstream interactions between lean premixed (50% $H_2$ + 50% CO)-air and $CH_4$-air flames.

• Journal of Hydrogen and New Energy
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• v.26 no.4
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• pp.347-356
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• 2015

A study has been conducted numerically to investigate the lifted flat syngas flame structure of impinging jet flame configuration with the global strain rates in 10% hydrogen content. In this study, the effects of strain rate were major parameters on chemistry kinetics and flame structure at stagnation point. The numerical results were calculated by SPIN application of the CHEMKIN package. The strain rates were adjusted with Reynolds numbers of premixed syngas-air mixture. Different flame shapes were observed with different strain rates. As strain rate has increased, the flame temperature and axial velocity have been decreased due to the flame heat loss increment, and the OH radical reaction zones become narrower but each mole fractions are still constant. Also, the reversion of $H_2O$ product near stagnation point has been found out when strain rate has increased. This phenomenon is attributed to the rapid production of oxidizing radical reaction such as the R12 ($H+O_2(+M)=HO_2(+M)$), which makes the R18 ($HO_2+OH=O_2+H_2O$) reaction increment.

• Journal of Hydrogen and New Energy
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• v.25 no.1
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• pp.47-58
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• 2014

The characteristics of flame shape, laminar burning velocity, emissions and heat flux of stagnation point in premixed impinging jet flame of syngas fuel with 10% hydrogen content were experimentally investigated. Also, the adiabatic temperature and burning velocity are calculated by Chemkin package with USC-II mechanism. The equivalence ratios(0.8~5.0) and dimensionless separation distance(2.0~5.0) with fixed Reynolds number(1800) are main parameters in this work. Different flame shapes and colors were observed for different impingement conditions. The experimental results of burning velocity by flame surface area have a consistent with previous works and numerical simulation of this work. The inner flame length could be predicted with the ratio of mixture velocity and burning velocity from a simple formulation by the laminar burning velocity definition. It has been observed that the heat fluxes at stagnation point are directly affected by the flame shape including the separation distance. The emission results in impinging flame of syngas fuel show that the characteristics of $NO_x$ emission traced well with adiabatic temperature trend and CO emission due to fuel rich condition increased continuously with respect to the equivalence ratio.

• Journal of Energy Engineering
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• v.11 no.4
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• pp.350-358
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• 2002

The present work determined the flame structure characteristics of coal syngas combusted inside swirl burners with various nozzle types. Fuel nozzle types are largely classified into two groups of axial and tangential. Experiments were carried out for investigating the effects of fuel nozzle geometry, fuel composition ratio, heating rate, excess air, and degree of swirl on the turbulent diffusion flame structure. To determine the characteristics of the flame structure, axial type fuel nozzle diameter of laboratory-scale combustor is varied to 1.23, 1.96, and 2.95 ㎜ and the direction of tangential type nozzles are varied to radial, clockwise, and counter-clockwise. The comparison of the experimental results was performed to understand functional parameters relating the flame structure. Data analysis showed that the vertical straight flame height generally decreased with increasing swirl number and decreasing axial type nozzle diameter. Flame height established with tangential type nozzle is 3 times shorter than that with vertical type. The flame structures among the 3 different tangential fuel nozzles relatively showed no particular difference. By increasing the heating rate, the width of flame increased generally in both vertical and tangential flame. Within the present experimental parameters of the investigation, flame structure is mainly depends on the nozzle type of the combustor. The visually investigated flame lengths are confirmed through the analysis of temperature profile of each flame.

• Journal of Hydrogen and New Energy
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• v.31 no.5
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• pp.467-479
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• 2020

Various researches are being conducted to reduce greenhouse gases generated by the consumption of traditional energy resources. This study was conducted to numerically analyze the combustion characteristics and N-S reaction behavior with respect to the H₂ content of syngas composed of CO and H₂ in pressurized air combustion. A non-premixed opposed flow flame model was applied a modified detailed mechanism with S-chemistry was developed based on GRI 3.0 to simulate the syngas reaction. As the hydrogen content increased, the flame thickness increased due to the fast reactivity of hydrogen. In the rich region, NO and SO₂ were reduced by reaction with H radical and H bonding of NO was suppressed by the formation of HOSO.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.371-374
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• 2011

High-resolution numerical study is carried out to investigate the flame stability of the turbulent supersonic combustion in a Dual-Combustion Ramjet (DCR). The auto-ignition in a shear layer between hydrogen/carbon-monoxide syngas and air was studied at elevated enthalpy condition. Comparison of a constant area combustor and a combustor with a small divergence angle shows that the supersonic combustion has a characteristics of the lifted flame and its stability is influenced significantly by the compressibility.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.349-352
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• 2008

This study has numerically modeled the combustion processes of the turbulent swirling premixed lifted syngas flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially-injected air jets induce the turbulent swirling flow which plays the crucial role of stabilizing the turbulent lifted flames. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flamelet model. Numerical results indicate clearly that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling premixed lifted flames in the low-swirl burner. Computations are made for the wide range of the syngas chemical composition and the dilution level at two pressure conditions (1.0, 5.0 bar). Numerical results indicate that the lifted height in the LSB is increased by decreasing the H2 percentage and increasing the dilution level at the given equivalence ratio. It is also found that the flashback is occurred for the hydrogen composition higher than 80% at the equivalence ratio, 0.8. However, at the syngas composition range in the IGCC system, the stable lean-premixed lifted flames are formed at the low-swirl burner.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.225-226
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• 2014

An experimental study has been conducted to investigate the heat transfer characteristics of syngas/air mixture impinging jet flame with 10% hydrogen content. Effects of impinging distance, Reynolds number as major parameters on surface temperature of stagnation point were examined experimentally by the data acquisitions from k-type thermocouple. There were 2 times of maximum peak point of stagnation point with respect to the impinging distance for the investigation. As reynolds number increases, the nusselt number and convective heat transfer coefficient increased accordingly.

• Journal of the Korean Society of Combustion
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• v.17 no.3
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• pp.17-29
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• 2012

The effects of strain rate and preferential diffusion of $H_2$ on flame extinction are numerically studied in interacting premixed syngas-air flames with fuel compositions of 50% $H_2$ + 50% CO and 30% $H_2$ + 70% CO. Flame stability diagrams mapping lower and upper limit fuel concentrations at flame extinction as a function of strain rate are examined. Increasing strain rate reduces the boundaries of both flammable lean and rich fuel concentrations and produces a flammable island and subsequently even a point, implying that there exists a limit strain rate over which interacting flame cannot be sustained anymore. Even if effective Lewis numbers are slightly larger than unity on extinction boundaries, the shape of the lean extinction boundary is slanted even at low strain rate, i.e. $a_g=30s^{-1}$ and is more slanted in further increase of strain rate, implying that flame interaction on lean extinction boundary is strong and thus hydrogen (as a deficient reactant) Lewis number much less than unity plays an important role of flame interaction. It is also shown that effects of preferential diffusion of $H_2$ cause flame interaction to be stronger on lean extinction boundaries and weaker on rich extinction boundaries. Detailed analyses are made through the comparison between flame structures with and without the restriction of the diffusivities of $H_2$ and H in symmetric and asymmetric fuel compositions. The reduction of flammable fuel compositions in increase of strain rate suggests that the mechanism of flame extinction is significant conductive heat loss from the stronger flame to ambience.