• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.7
• /
• pp.1022-1029
• /
• 1998

The relation of the inlet fuel distribution, velocity, and overall equivalence ratio to the stability of a lean burning no-swirl dump combustor was examined. Premixed or partially premixed natural gas was introduced into the air stream, which flowed to the dump region through an annular inlet pipe. Inlet air was preheated upto 400 deg.C. Combustion instability was observed to occur at higher value of equivalence ratio (> 0.6) as the degree of unpremixedness was increased. Instabilities exhibited a dominant frequency of ~ 500 Hz, which corresponded to a half wave mode of combustor. CH chemiluminescence and pressure fluctuations were in-phase when combustion instabilities occurred. Acetone LIF images revealed that there was a strong fuel concentration gradient across the inlet annulus. Phase resolved OH LIF images showed that inlet fuel distribution was affected by the combustion instabilities.

• Journal of the Korean Society of Combustion
• /
• v.14 no.1
• /
• pp.31-38
• /
• 2009

The effects of acoustic excitation of coaxial air on mixing enhancement and reduction of nitrogen oxides (NOx) emission were investigated. A compression driver was attached to the coaxial air supply tube to impose excitation. Measurements of NOx emission with frequency sweeping were performed to observe the trend of NOx emission according to the fuel and air flow conditions and to inquire about the effective excitation frequency for reducing NOx. Then, Schlieren photographs were taken to visualize the flow field and to study the effect of excitation. In addition, phase-locked particle image velocimetry (PIV) was performed to acquire velocity field for each case and to investigate the effect of vortices more clearly. Direct photographs and OH chemiluminescence photographs were taken to study the variation of flame length and reaction zone. It was found that acoustic forcing frequencies close to the resonance frequencies of coaxial air supply tube could reduce NOx emission. This NOx reduction was influenced by mixing enhancement due to large-scale vortices formed by fluctuation of coaxial air jet velocity.

• Journal of Mechanical Science and Technology
• /
• v.19 no.6
• /
• pp.1366-1377
• /
• 2005

Experimental study was carried out in an atmospheric pressure, laboratory-scale dump combustor showing features of combustion instabilities. Flame structure and heat release rates were obtained from OH emission spectroscopy. Qualitative comparisons were made between line-integrated OH chemiluminescence image and Abel-transformed one. Local Rayleigh index distributions were also examined. Mean temperature, normalized standard deviation and temperature fluctuations were measured by coherent anti-Stokes Raman spectroscopy (CARS). To see the periodic behavior of oscillating flames, phase-resolved measurements were performed with respect to the pressure wave in the combustor. Results on system damping and driving characteristics were provided as a function of equivalence ratio. It also could be observed that phase resolved temperatures have been changed in a well-defined manner, while its difference between maximum and minimum reached up to 280K. These results would be expected to play an important role in better understanding of driving mechanisms and thermo-acoustic interactions.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.7
• /
• pp.603-610
• /
• 2016

This paper describes experimental results about emission and NOx reduction of dilution effect (Nitrogen and carbon dioxide) about various fuel compositions of synthetic natural gas (SNG). Combustion experiment was performed to investigate the combustion characteristics for SNG with various hydrogen ratio in SNG, heat input and equivalence ratio in a partially premixed model gas turbine combustor. NOx emission was similar to each hydrogen ratio and flame characteristics was investigated from OH chemiluminescence images. There was a singularity of CO emission in stoichiometric condition and it can be identified using OH chemiluminescence intensity. In addition, dilution effect was studied in using nitrogen and carbon dioxide as diluent to reduce the NOx emission. Carbon dioxide diluent was more effective to NOx reduction than nitrogen diluent because of its high diluent specific heat and its heat capacity.

• 한국연소학회:학술대회논문집
• /
• 2014.11a
• /
• pp.1-4
• /
• 2014

The present work focuses on the analysis of the pulverized coal combustion aerodynamics of the dual swirl burner by the control of the swirl-modes such as the outer swirl intensity (OSI). The detailed structure of pulverized coal swirling flames with swirl-mode was studied experimentally by particle image velocimetry and local flame colors based on $OH^*$, $CH^*$, and ${C_2}^*$ radicals. For all co-swirling conditions, the internal recirculation zone (IRZ) was observed near the inner shear layer with respect to the processing vortex core structure. Furthermore, a co-rotating vortex in the outer shear layer and the exhaust tube vortex (ETV) along the central axis were observed. The intensity of $CH^*$ signal was higher with small coal particle size, conversely, the size of the distribution of the $CH^*$ signal becomes larger. Therefore, the control of the aerodynamics with changing swirl intensities may play an important role in improving both environmental and combustion performances.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.1
• /
• pp.68-74
• /
• 2000

Experimental investigation on flame spread along suspended droplet arrays have been conducted with various droplet spacings and ambient air velocities. Especially, an opposed air stream is introduced to simulate fundamental flame spread behaviors in spray combustion. High-speed chemiluminescence imaging technique of OH radicals has been adopted to measure flame spread rates and to observe various flame spread behaviors. The fuel used is n-Decane and the air velocity varies from 0 to 17cm/s. The pattern of flame spread is grouped into two: a continuous mode and an intermittent one. It is found that there exists droplet spcings, above which flame spread does not occur. The increase of ambient air velocity causes the limit droplet spacing of flame spread to become small due to the increase of apparent flame stretch. As the ambient air velocity decreases, flame spread rate increases and then decreases after taking a maximum flame spread rate. This suggests that there exists a moderate air flowing to give a maximum flame spread rate due to enhanced chemical reaction by the increase of oxidizer concentration.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.9
• /
• pp.658-665
• /
• 2009

Lean premixed combustors are used for significant NOx reduction which one of issues in current gas turbine combustor. This study was investigated to estimate the effects of the unmixedness of fuel-air, equivalence ratio on the instability mechanism, NOx emission and combustion oscillation in a lean premixed combustor. The experiments were conducted in a dump combustor at atmospheric pressure conditions using methane as fuel. The swirler angle was $45^{\circ}$, the degrees of fuel-air mixing were 0, 50 and 100 and inlet temperature was 650K. The equivalence ratio was ranging from 0.5 to 0.8. This paper shows that NOx emission was increased when the degree of fuel-air mixing is increased in same equivalence ratio and when equivalence ratio is increased. And the range of the combustion instability was enlarged as a function of increasing of the degree of fuel-air mixing.

• Journal of the Korean Society of Combustion
• /
• v.17 no.1
• /
• pp.22-29
• /
• 2012

The detachment stability characteristics of syngas $H_2$/CO jet attached flames were studied. The flame stability was observed while varying the syngas fuel composition, coaxial nozzle diameter and fuel nozzle rim thickness. The detachment stability limit of the syngas single jet flame was found to decrease with increasing mole fraction of carbon monoxide in the fuel. In hydrogen jet flames with coaxial air, the flame detachment stability was found to be independent of the coaxial nozzle diameter. However, velocities of appearance of liftoff and blowout velocities of lifted flames have dependence. At lower fuel velocity range, the critical coaxial air velocity leading to flame detachment increases with increasing fuel jet velocity, whereas at higher fuel velocity range, it decreases. This increasing-decreasing non-monotonic trend appears for all $H_2$/CO syngas compositions (50/50~100/0% $H_2$/CO). To qualitatively understand the flame behavior near the nozzle rim, $OH^*$ chemiluminescence imaging was performed near the detachment limit conditions. For all fuel compositions, local extinction on the rim is observed at lower fuel velocities(increasing stability region), while local flame extinction downstream of the rim is observed at higher fuel velocities(decreasing stability region). Maximum values of the non-monotonic trends appear to be identical when the fuel jet velocity is normalized by the critical fuel velocity obtained in the single jet cases.

• Journal of the Korean Society of Combustion
• /
• v.3 no.2
• /
• pp.1-11
• /
• 1998

Experimental investigation on flame spread of blended fuel droplet arrays has been conducted for droplet diameters of 1.0mm and 0.75mm using high-speed chemiluminescence images of OH radical. The flame spread rate is measured with blended fuel composition, droplet diameter, and droplet spacing. Flame spread is categorized into two: a continuous mode and an intermittent one. There exist a limit droplet spacing, above which flame does not spread, and a droplet spacing of maximum flame spread, which is closely related to flame diameter. It is seen that flame spread rate is mainly dependent upon the relative position of flame zone within a droplet spacing. In case of large droplet, the increase of % volume of Heptane induces the shift of limit droplet spacing to a larger spacing since volatile Heptane plays a role of an enhancer of flame spread rate. In case of small droplet, the increase of % volume of Heptane leads to the shift of limit droplet spacing to a smaller droplet spacing. This is so because of the delayed chemical reaction time by the rapid increase of mass flux of fuel vapor for small droplet.

• 한국연소학회:학술대회논문집
• /
• 2013.06a
• /
• pp.109-110
• /
• 2013

This paper describes gas turbine combustion characteristics of synthetic natural gas which contains a small amount hydrogen content. By conducting ambient pressure high temperature combustion test at gas turbine relevant combustor geometry, the combustion characteristics such as combustion instability, NOx and CO emission, temperatures at turbine inlet, nozzle and dump plane, and flame structure from high speed OH chemiluminescence images were investigated when changing hydrogen content from zero to 5%. From the results, qualitative and quantitative relationships are derived between key aspects of combustion performance, notably NOx/CO emission and combustion instability. Natural gas containing hydrogen up to 5% does not show significant difference in view of all combustion characteristics except combustion instability. Only up to 1% hydrogen addition could not change the pressure fluctuation and phase gas between fluctuations of pressure and heat release. From the results, it can be concluded that synthetic national gas which contains 1% of hydrogen can be guaranteed for the stable and reliable operation of natural gas firing gas turbine.