• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.2
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• pp.232-240
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• 1986

Extinction characteristics of the two interacting premixed flames are analyzed for the effects of flame stretch and preferential diffusion using large activation energy asymptotic analysis by adopting counterflow system as a model problem. Results show that the flammable limit of the thermally interacting premixed flames is extended compared to the single flame, and the extinction mechanism is classified into weak and strong interactions. As the lewis number of the deficient species increases, the region of strong interaction diminishes which can explain the different characteristics of the extinction boundaries of the lean (rich) methane/air and butane/air flames. The influence of the flame stretch to the interaction boundaries is also studied.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.7-8
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• 2012

The effects of interaction between partially premixed and premixed swirl flames on CO and NOx emissions were experimentally investigated using a hybrid/dual swirl jet combustor for a micro-gas turbine. Under the condition of constant angle ($45^{\circ}$) for outer swirl vane, the angle and direction of inner swirl vane installed for a partially premixed flame were varied as main parameters with a constant fuel flow rate for each nozzle. It was found that for all conditions, CO and NOx emissions were measured below 4 ppm and 15 ppm at 15% $O_2$, respectively, in a wide range of equivalence ratio (0.6~0.9). For co-swirl flows, CO emission increased dramatically as the angle of inner swirl vane increased from $15^{\circ}$ to $45^{\circ}$ near lean-flammability limit (i.e. equivalence ratio of 0.5). On the other hand, the case of swirl $angle=45^{\circ}$ provided the lowest NOx emission at higher equivalence ratios than 0.6. For counter-swirl flows, the case of swirl $angle=45^{\circ}$ extended the lean-flammability limit but higher NOx emissions were found compared to those of co-swirl flows. These results could be inferred by interaction between (inner) partially premixed and (outer) premixed swirl flames. However, these estimations were not clear yet because there was insufficient data on turbulent flow structure and fuel-air mixing in the present experimental approach.

• Journal of ILASS-Korea
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• v.8 no.4
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• pp.9-16
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• 2003

The Purpose of this study is to investigate the relationships between the local heat release rate and CH concentration have been investigated by numerical simulations of methane-air premixed flames. And simultaneous CH and OH PLIF(Planar Laser Induced Fluorescence) measurement has been also conducted for lean premixed flame as well as for laminar flames. Numerical simulations are conducted for laminar premixed flames and turbulent ones by using PREMIX in CHEMKIN and two dimensional DNS code with GRI mechanism version 2.11, respectively. In the case of laminar premixed flame, the distance between the peak of heat release rate and that of CH concentration is under $91{\mu}m$ for all equivalence ratio calculated in present work. Even for the premixed flame in high intensity turbulence, the distribution of the heat release rate coincides with that of CH mole fraction. For CH PLIF measurements in the laminar premixed flame burner, CH fluorescence intensity as a function of equivalence ratio shows a similar trend with CH mole fraction computed by GRI mechanism. Simultaneous CH and OH PLIF measurement gave us useful information of instantaneous reaction zone. In addition, CH fluorescence can be measured even for lean conditions where CH mole fraction significantly decreases compared with that of stoichiometric condition. It was found that CH PLIF measurements can be applicable to the estimation of the spatial fluctuations of heat release rate in the engine combustion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1257-1264
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• 2011

This paper presents 3D simulation by STAR-CCM+ for lean premixed combustion in a stationary gas turbine combustor with separate pilot and main nozzles. The constant for the source term in the flame area density transport equation was modified to account for a low global equivalence ratio and validated against measurement data. A Partially-premixed Coherent Flame Model(PCFM) involves propagation of a laminar premixed flame with the predicted flame surface density and equilibrium assumption in the burned gas with spatial inhomogeneity. The conditions for cooling by radiation and convection are considered for accurate determination of the heat flux on the wall. A parametric study is of the pilot-fuel-to-total-fuel-ratio is carried out. A chemical reactor network (CRN) was constructed on the basis of the 3D simulation results and compared against measurements of NOx.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.279-282
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• 2002

Recently, gas turbines for power generation adopt multistage DLN(Dry Low NOx) type combustion, where diffusion combustion is applied at low load and, with increase in load, the combustion mode is changed to lean premixed combustion to reduce NOx emissive concentration. However, during the mode changeover from diffusion to premixed flame, unfavorable phenomena, such as flashback, high amplitude combustion oscillations, or thermal damage of combustor parts could frequently occur. In the present study, to apply for the analysis of such unfavorable phenomena, three-dimensional CFD investigations are carried out to compare the detailed flow characteristics and temperature distribution inside the gas turbine combustor before and after combustion mode changeover. The fuel considered here is pure methane gas. A standard $k-{\varepsilon}$ turbulence model with wall function and a P-N type radiation heat transfer model, have been utilized. To analyze the complex geometric effects of combustor parts on combustion characteristics, fuel nozzles, a swirl vane f3r fuel-air mixing, and cooling air holes on the combustor liner wall, are included in this simulation.

• Journal of the Korean Society of Combustion
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• v.6 no.2
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• pp.43-49
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• 2001

Instantaneous, three-dimensional scalar dissipation rates of the reaction progress variable are measured in turbulent premixed Bunsen flames of lean hydrocarbon/air mixtures with the two-sheet, two-dimensional Rayleigh scattering technique. The flames investigated are located in the turbulent flame-front regime on a newly proposed combustion diagram for premixed flames. The conditionally-averaged mean scalar dissipation rates, $N_{\zeta}$ are found to be lower than the calculated laminar values, indicating a locally broadened flame front. In agreement with previous measurements, the maximum of $N_{\zeta}$, decreases strongly with increasing Karlovitz numbers. The conditional probability density functions are close to a log-normal distribution for scalar dissipation rates conditioned at the progress variable value where the scalar dissipation is maximum in unstretched laminar flame calculations. The time scale for the Favre-averaged mean scalar dissipation rate decreases in general across the turbulent flame brush from the unburnt to burnt side.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.201-207
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• 1999

The combustion characteristics for the low NOx 50 kW-class gas turbine combustor have been experimentally investigated. In order to achieve the premixing and the lean burn combustion, the geometries of the primary zone including premixed chamber were modified from conventional combustor. The centerline profiles of CO and NO concentration, and temperature were measured for the premixed combustors with or without dilution holes in the liner. The effects of the pilot fuel injection rate and air dilution on flame stabilization and pollutant (CO, NO) emission are discussed in detail.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.365-373
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• 2010

A chemical reactor model (CRM) was developed for a jet stirred reactor (JSR) to predict the emission of exhaust such as NOx. In this study, a two-PSR model was chosen as the chemical reactor model for the JSR. The predictions of NO formation in lean premixed methane-air combustion in the JSR were carried out by using CHEMKIN and GRI 3.0 methane-air combustion mechanism which include the four NO formation mechanisms. The calculated results were compared with Rutar's experimental data for the validation of the model. The effects of important parameters on NO formation and the contributions of the four NO pathways were investigated. In the flame region, the major pathway is the prompt mechanism, and in the post flame region, the major pathway is the Zelodovich mechanism. Under the lean premixed condition, the N2O mechanism is the important pathway in both flame and postflame regions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.225-232
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• 2012

A chemical reactor network (CRN) was developed for a lean premixed gas turbine combustor to predict the emission of pollutants such as NOx and CO. In this study, the predictions of NOx and CO emissions from lean premixed methane-air combustion in the gas turbine were carried out using CHEMKIN and a GRI 3.0 methane-air combustion mechanism, which includes the four NO formation mechanisms for various load conditions. The calculated results were compared with experimental data obtained from a modified test combustor to validate the model. The contributions of the four NO pathways were investigated for various load conditions. The effects of nonuniformity of the mass flux and of the equivalence ratio of the injector on the NOx formation were investigated, and a method of reducing the pollutant formation was suggested for the development of a sub-10 ppm gas turbine combustor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.425-432
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• 2004

The objective of this study is a qualitative comparison between line-integrated OH chemiluminescence(OH$\^$*/) image and its Abel inverted image to investigate the flame structure at different phase of the oscillating pressure field. PIV(Particle Image Velocimetry) measurements were conducted under non-reacting conditions to see the global flow structure and NOx emission was measured to investigate the effect of fuel-air premixing on combustion instability and emission characteristics. Experiments were carried out in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas. Combustion instabilities in present study exhibited a longitudinal mode with a dominant frequency of ∼341.8㎐, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instability occurred. Results gave an insight about the location where the strong coherence of pressure and heat release existed. Also an additional information on active control to suppress the combustion instabilities was obtained. For lean premixed combustion, strong correlation between OH$\^$*/ and NOx emissions was expected largely due to the exponential dependence of thermal NOx mechanism on flame temperature.