• Journal of the Korean Institute of Gas
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• v.25 no.6
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• pp.22-28
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• 2021

Combustion characteristics were examined experimentally for a swirl-stabilized double cone premixed burner nozzle used for industrial gas turbines for power generation. An original model and a variant with a different fuel injection pattern are tested to compare their combustion characteristics such as NOx, CO and stability in pressurized conditions with single burner-flame and in an ambient multi-flame conditions with multi-burners. Test results show that NOx emissions are smaller for the variant, whose number of fuel holes is reduced with the same total area of fuel holes, in ambient and pressurized single-flame conditions with single burner, which results from enhanced fuel/air mixing due to a higher penetration of fuel into the air stream. The multi-burnerflame test results show that NOx emissions are smaller for the variant due to reduced flame interactions, which, on the contrary, slightly reduces the stability margin. On-site test results fromin an actual power plants also show that NOx emissions are reduced for the variant, compared with the original one, which is in agreement with the lab test results stated above.

• 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.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.85-90
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• 2004

We have presented characteristics of a transitional behavior from a premixed flame to a triple flame in a lifted flame according to the change of equivalence ratio. The experimental apparatus consisted of a slot burner and a contraction nozzle for a lifted flame. As concentration difference of the both side of slot burner increases, the shape of flame changed from a premixed flame to a triple flame, and the liftoff height is decreased to the minimum value and then increase again. Around this minimum point, it is confirmed a transition regime from premixed flame to triple flame. Consequently, the experimental results of the liftoff height, flame curvature and luminescence intensity showed that the stabilized laminar lifted flame regime is categorized by regimes of premixed flame, triple flame and critical flame. In the visualization experiment of smoke wire, the flow divergence and redirection reappeared in premixed flame as well as triple flame. Thus we cannot express the flame front of lifted flame has a behavior of triple flame with only flow divergence and redirection. To differentiate triple flame and premixed flame, ${\Phi}$ value of partially premixed fraction is employed. The partially premixed fraction ${\Phi}$ was constant in premixed flame. In critical flame small gradient appears over the whole regime. In triple flame, typical diffusion flame shape is obtained as parabolic distribution type due to diffusion flame trailing.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.29-36
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• 2010

An experimental study was conducted for three different fuels($CH_4$, $C_2H_4$ and $C_3H_8$) to investigate the combustion characteristics and the local reaction intensity with combustor pressure(-30kpa~30kpa). Regardless of fuel composition, EINOx decreased with reducing pressure decreased. Structure and combustion characteristics were also largely affected by the combustor pressure. In addition, reaction intensity in terms of the changing combustor pressure and equivalence ratio was investigated. Combustion reaction in higher than atmospheric pressure was very active than the lower combustor pressure. When the combustor pressure is lower than the atmospheric pressure, the overall reactivity is noticeably enhanced due to the elevated diffusion process of unburned mixture. It was found that the combustion characteristics of the methane and propane flames are considerably influenced by the pressure while those of ethylene flame are less sensitive to the combustor pressure.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.75-81
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• 2003

In this paper, the study of effects of flow variables on flame structure and NOx emission concentration was performed in co-axial laminar partially premixed methane/air flames. the objectives are to reveal its effect as parameters were varied and to understand the correlation between flame structure and NOx emission characteristics in the reaction zone. equivalence ratio(${\Phi}$), fuel split degree(${\sigma}$), and mixing distance(x/D) were defined as a premixing degree and varied within $1.36{\sim}3.17$(equivalence ratio), $50{\sim}100$(fuel split degree), and $5{\sim}20$(mixing distance). the image of $OH{\ast}$ and $CH{\ast}$, and NOx concentration were obtained with an ICCD camera and a NOx analyzer. additionally the maximum intensity location of $OH{\ast}$ chemiluminescence and $CH{\ast}$ chemiluminescence were measured to compare each flame structures. In conclusion flame structure and NOx emission characteristics were changed from diffused to premixed flame when mixing degree was on the increase. the main effect on flame structure and NOx production was at first equivalence ratio(${\Phi}$), and next fuel split degree(${\sigma}$), and finally mixing distance(x/D).

• Journal of the Korean Society of Combustion
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• v.14 no.2
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• pp.26-31
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• 2009

Adding small amounts of air to the fuel is used in many commercial combustors to avoid sooty flame. But partially premixed jet flame has lower blowout velocity, $u_{b.o}$, than nonpremixed one. Increasing blowout limit would be one of the key factors to develope highly intense compact combustion devices. Swirling flow enhances fuel and air mixing and induces a highly turbulent recirculation zone, which helps flame stabilization. It was known that NOx emission decreases with swirl on the proper range of swirl number. And it was shown that the flame interaction in multiple jets also increases $u_{b.o}$ owing to the internal recirculation and reduces NO emission. If the effects of swirl and flame interaction are combined together in partially premixed flame, both $u_{b.o}$ increasement and NOx emission reduction could be achieved. Blowout limits of partially premixed interacting propane flame in the swirling air coflow are investigated experimentally. The results show that the flame is not extinguished up to the experimental limits, 210 m/s, at the swirl number of 0.32 and $X_{F,o}$ = 0.46.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.91-98
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• 2000

We investigated a uniform temperature zone, produced by double flame structure of a co flow CH4/air partially premixed flame, to be used as a temperature calibration source for laser diagnostics. A broadband N2 CARS(coherent anti-Stokes Raman spectroscopy) system with a modeless laser was used for temperature measurement. When the stoichiometric ratio was 1.5, we found the uniform temperature zone in radial direction of the flame of which the averaged temperature was 2110 K with standard deviation 24 K. In the stoichiometric ratio range between 2.0 and 2.5, we found very stable temperature-varying zones in vertical direction at the center of the flame. The size of the zone was approximately 15 mm and it covered a temperature range from 300 K to 1900 K. We also suggest that this zone can be used as a calibration source for 2-D PLIF(planar laser induced flurescence) temperature measurement.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.54-60
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• 2017

In order to identify the characteristics of the flame transfer function gain, cold-flow transfer function was introduced, which is the part of the combustion instability research. Nitrogen and carbon dioxide was used to obtain the cold-flow transfer function and input/output variables was measured by hot wire anemometry. Density and fluid flow rate affect the cold-flow transfer function gain and peak frequency. In addition, acoustic resonance frequency affects the peak frequency of gain in the fuel feeding line.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.6
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• pp.98-106
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• 2011

This paper reviews the state-of-the-art thermoacoustic(TA) modeling techniques and research trend to predict major parameters determining combustion instabilities in lean premixed gas turbine combustors. Linear TA modeling results give us an information on eigenfrequencies and initial growth rate of the instabilities. For the prediction, linear relation equation between acoustic waves and heat release oscillations should be derived in the determined system. Key information for this analysis is to determine the heat release fluctuations in the combustor, which is typically obtained by using n-${\tau}$ function from flame transfer function measurements and/or predictions. Great advancement in the linear TA modeling has been made over a couple of decades, and some successful prediction results have been reported in actual gas turbine combustors. However nonlinear TA model developments which are required to analyze nonlinear system behaviors such as limit cycle saturation and transition phenomena are still limited in a very simple system. In order to fully understand combustion instabilities in a complicated real system, nonlinear flame dynamics and acoustic wave interaction with nonlinear system boundary conditions should be explained from the nonlinear TA model developments.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.4
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• pp.77-84
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• 2001

Measurements of local CO, $CO_2$, $O_2$, $N_2$, $C_3$H$_{8}$, NOx concentrations and flame temperature are made for partially premixed flame with and without acoustic excitation. The CO, $CO_2$, $O_2$, $N_2$, and $C$_3$H_8$ concentrations are determined by thermal conductivity detection (Gas-chromatograph) and NOx concentrations are determined by chemiluminescent detection (NOx analyser). To measure local sample concentration, sampling probe was made by quartz with inlet diameter of 0.25mm. In the case of excitation, the visual shape of the flame is changed from laminar flame to turbulent-like flame. The flame length is also reduced, and the flame width becomes broad. In the observation of emission concentration without acoustic excitation, meanwhile, the $CO_2$ and NOx concentrations peak at flame front where the mixture meets with surrounding air, and the CO concentration is increasing at maximum position of CO2 concentration and peaks at the centerline of the burner. In the case of acoustic excitation, the $CO_2$ concentration is widely occurred at nozzle of the burner and is higher relative to unexcitation. The CO concentration is much reduced, but NOx concentration is more increasing. And flame temperature is higher relative to unexcitation. These are caused by enhancing of mixing with surrounding air due to excitation. However, in the case of acoustic excitation, the total NOx concentration is reduced because of the shortened flame length which affects residence time.e.