Kee-Man Lee

Development of Hybrid/Dual Jet Combustor for a MGT (Part I: Experimental Study on Geometric Optimization)

Corresponding author. E-mail: kmlee@scnu.ac.krABSTRACT An optimum configuration of the hybrid/dual swirl jet combust or for a micro-gas turbine was investigated experimentally. Location of pilot nozzle, angle an d direction of swirler vane were varied systematically as main parameters under the conditions of const ant thermal load. The results showed that the variation in locations of inner fuel nozzle and pilot burner resulted in significant change in flame shape and swirl intensity due to the changes in recircula ting flow pattern and minimum flow area near burner exit, in particular, with the significant reduction of CO emission near lean-flammability limit. In addition, it was observed that the co-swirl configuration produced less CO and NOx emissions compared to the counter-swirl configuration.초 록 마이크로 가스터빈용 하이브리드/이중 선회 제트 연소기의 형상 최적화에 대한 실험연구가 수행되었다. 고정된 열부하에서 pilot 버너의 위치 및 선회기 베인의 방향이 주요 변수로 검토되었다. 주요 결과로서, pilot 버너 및 연료 노즐의 위치변화는 버너 출구 근처의 최소 유동면적 및 재순환 유동패턴의 변화를 발생시키며, 이로 인하여 선회강도 및 화염형상이 큰 영향을 받게 된다. 선회기 베인 각도의 증가(30°에서 45°)는 희박가연한계 근처에서 CO 배출량을 크게 저감시킨다. 추가로 정방향 선회형상이 역방향 선회형상에 비해 보다 낮은 CO 및 NOx 배출량을 갖게 됨을 확인하였다.Key Words: Micro-gas Turbine(마이크로 가스터빈), Hybrid/Dual Swirl Jet Combustor(하이브리드 이중 선회제트 연소기), Lean-premixed Combustion(희박 예혼합연소)Received 9 June 2013 / Revised 11 September 2013 / Accepted 17 September 2013

A Study on the Laminar Burning Velocity of Synthetic Gas of Coal Gasification(H 2 /CO)-Air Premixed Flames

Syngas laminar burning velocity measurements were carried out at atmospheric pressure and ambient temperature using the Bunsen flame configuration with nozzle burner as a fundamental study on flame stability of syngas fuel. Representative syngas mixture compositions (:CO) such as 25:75%, 50:50% and 75:25% and equivalence ratios from 0.5 to 1.4 have been conducted. Average laminar burning velocities have been determined by the stabilized nozzle burner flames using the angle method, radical surface area method and compared with the data obtained from the other literatures. And the results of each experimental methodologies in the various composition ratios and equivalence ratios were coincided with the result of numerical simulation. Especially, it was confirmed that there was necessary to choice a more accurate measurement methodology even the same static flame method for the various composition ratios of syngas fuel including hydrogen. Also, it was reconfirmed that the laminar burning velocities gradually increased with the increasing of hydrogen content in a fuel mixture.

A visual study on turnabout phenomenon of vortex roll-up in forced jet diffusion flames

An experimental study on the effect of forcing amplitude in forced jet diffusion flames has been conducted. Various flow visualization techniques are employed using optical schemes, including light scattering photography, high speed imaging by motion analysis, and determination of velocity vector and vorticity fields from PIV data. Particular attenttion is focused on the turnabout mechanism around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. In particular, we present a schematic diagram that aids in the understanding of the turnabout mechanism of vortex roll-up. This diagram explains why the forced flame is elongated under moderate forcing amplitudes but shortens again when the forcing amplitude is further increased.

Development of Hybrid/Dual Swirl Jet Combustor for a MGT (Part II: Numerical Study on Isothermal Flow)

The isothermal flow structure and mixing characteristics of a hybrid/dual swirl jet combustor for micro-gas turbine (MGT) were numerically investigated. Location of pilot burner, swirl angle and direction were varied as main parameters with the identical thermal load. As a result, the variations in location of pilot nozzle, swirl angle and direction resulted in the significant change in turbulent flow field near burner exit, in particular, center toroidal recirculation zone (CTRZ) as well as turbulent intensity, and thus the flame stability and emission performance might be significantly changed. With the comparison of experimental results, the case of swirl angle 45 o and co-swirl flow including optimum location of pilot burner were chosen in terms of the flame stability and emissions for the development of hybrid/dual swirl jet combustor.

NOx Formation Characteristics on Heat Loss Rate for CH4/Air Premixed Flames in a Perfectly Stirred Reactor

Abstract The effect of heat loss rate on NOx formation of CH 4 /air premixed flame were examined numerically in a perfectly stirred reactor. The following conclusions were drawn. Under the adiabatic wall condition, an increase in the residence time causes a remarkable increases in NOx emission. Under the heat loss conditions, however, NOx decreases significantly as the heat transfer coefficient and residence time increase. As the heat loss rate increases, Thermal NO mechanism and Re-burning NO mechanism play an important role in the NOx reduction, but Prompt NO mechanism and N 2 O-intermediate NO mechanism lead to the increase in NOx production. Although the NOx formation is actually related to complex NOx mechanism with the changes in the heat transfer coefficient and residence time, it was found that NOx concentration can be represented by independent Thermal NO mechanism. From these results, new NOx correlation combined with the heat loss rate and residence time was suggested for predicting the NOx concentration in a practical CH

A Study on the Flame Shape and the Interaction between Pilot and Main Flames in a Dual Swirl Combustor

Flame behaviors and interaction between pilot and main flames in a dual swirl combustor were investigated experimentally and numerically. Under the condition of fixed swirl angle of 45 for main flame, the swirl angle of pilot flame, total heat release rate and equivalence ratio of main flame were used as major parameters. As a result, detailed flame stability diagram of dual swirl combustor was identified in terms of 5 flame modes with the changes in total heat release rate and equivalence ratio of main flame. It was found that the swirl angle of pilot flame plays the most important role in the changes in flame location and overall flow structure inside the combustor, and thus leads to the significant change in the interaction between pilot and main flame.

A Study on the Mixing Capacity of Lifted Flame by the Nozzle Hole-tone of High Frequency in Non-premixed Jet Flames

Abstract. An experimental investigation of the characteristic of non-premixed lifted flames with nozzlehole-tone of high-frequency has been performed. Before the fuel was supplied to nozzle, the fuel was sup-plied through a burner cavity which was located under the nozzle. The fuel passed through the excitationcavity under the influence of the high-frequency affects the lifted flame characteristics. The measurementswere performed in flow range that occurs lifted flame and blow out. When the high-frequency is generatedfrom burner cavity, the lifted length became shorter, and noise reduced comparing to unexcitation case.Additionally, operating flow range was increased and diameter of flame base became smaller with high-frequency effect. Through this experiments, its ascertained that the high-frequency excitation can beadopted with effective method for flame stability and noise reduction.Key Words:Lift-off flame(부상화염), Hole-tone(구멍음), Combustion noise(연소소음), Flame stability(화염안정화) 기호설명

An Experimental Study on the Flame Appearance and Heat Transfer Characteristics of Acoustically Excited Impinging Inverse Diffusion Flames

Abstract An experimental investigation of the flame appearance and heat transfer characteristics in both unexcited and excited impinging inverse diffusion flames with a loud speaker has been performed. The flame is found to become broader and shorter (in length) with acoustic excitation. The heat flux at the stagnation point is increased with the acoustic excitation. The acoustic excitation is more effective in lean conditions than in rich conditions. The reasons for these behaviors are that acoustic excitation improves the entrainment of surrounding air into the jet. From this study, it is found that the maximum increase of 57% in the total heat flux is obtained at the stagnation point of Φ =0.8. Therefore, it is ascertained that the excitation combustion can be adopted with effective instruments as a method for improving heat transfer in impinging jet flames.요 약 본 오디오 스피커로 음향 가진과 비가진 된 충돌 역 확산화염에서 화염의 형상과 열전달 특성에 관한 실험적 연구를 수행하였다. 가진에 의해 화염은 반응대가 넓어지고 화염 길이는 좀 더 짧아지는 경향을 보이며 충돌판의 정체점에서 열전달 성능인 열유속은 가진에 의해 향상되는 것으로 나타났다 . 이러한 가진 효과는 당량비가 높은 과농한 상태 보다 상대적으로 낮은 혼합 상태에서 효과적으로 영향을 미치는 것으로 파악되는데 이는 가진에 의해 주위 산화제가 연료 분류로의 유입이 향상되어 나타나는 것으로 판단된다. 이러한 현상으로 본 연구에서는 당량비가 0.8인 경우 정체점에서 총 열유속이 최대 57% 증가되는 것으로 나타났다. 따라서 본 연구를 통해 가진 연소가 충돌 분류 화염에서 열전달 성능을 향상시키는데 효과적인 방법임을 확인하게 되었다 .

An Investigation of the Heat Loss Model for Predicting NO Concentration in the Downstream Region of Laminar CH4/Air Premixed Flames

One-dimensional modeling of CH4/air premixed flame was conducted to validate the heat loss model and investigate NOx formation characteristics in the postflame region. The predicted temperature and NO concentration were compared to experimental data and previous heat loss model results using a constant gradient of temperature (100 K/cm). The following conclusions were drawn. In the heat loss model using steady-state heat transfer equation, the numerical results using the effective heat loss coefficient (heff) of 1.0 W/m 2 K were in very good agreement with the experiments in terms of temperature and NO concentration. On the other hand, the calculated values using the constant gradient of temperature (100 K/cm) were lower than that in the experiments. Although the effects of heat loss suppress NO production near the flame region, a significant difference in NO concentration was not found compared to that under adiabatic conditions. In the postflame region, however, there were considerable differences in NO emission index as well as the contribution of NO formation mechanisms. In particular, in the range of 0.8