알루미나이드 확산코팅된 스테인레스 합금의 내산화 및 내삭마 특성

황철홍,이효민,오정석,황동현,황유석,이종원,최정묵,박준식,Hwang, Cheol Hong,Lee, Hyo Min,Oh, Jeong Seok,Hwang, Dong Hyeon,Hwang, Yu Seok,Lee, Jong Won,Choi, Jeong Mook,Park, Joon Sik 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.5

Stainless steel, a type of steel used for high-temperature parts, may cause damage when exposed to high temperatures, requiring additional coatings. In particular, the Cr₂O₃ product layer is unstable at 1000℃ and higher temperatures; therefore, it is necessary to improve the oxidation resistance. In this study, an aluminide (Fe₂Al₅ and FeAl₃) coating layer was formed on the surface of STS 630 specimens through Al diffusion coatings from 500℃ to 700℃ for up to 25 h. Because the coating layers of Fe₂Al₅ and FeAl₃ could not withstand temperatures above 1200℃, an Al₂O₃ coating layer is deposited on the surface through static oxidation treatment at 500℃ for 10 h. To confirm the ablation resistance of the resulting coating layer, dynamic flame exposure tests were conducted at 1350℃ for 5-15 min. Excellent oxidation resistance is observed in the coated base material beneath the aluminide layer. The conditions of the flame tests and coating are discussed in terms of microstructural variations.

CH₄/Air 예혼합화염의 하류영역에서 체류시간 및 열손실에 의한 NOx의 생성특성

황철홍,현승호,탁영조,이창언,Hwang, Cheol-Hong,Hyun, Sung-Ho,Tak, Young-Jo,Lee, Chang-Eon 대한기계학회 2007 大韓機械學會論文集B Vol.31 No.1

In this study, the NOx formation characteristics of one-dimensional $CH_4$/Air premixed flame using detailed-kinetic chemistry are examined numerically. The combustor length and the amount of heat loss are varied to investigate the effect of residence time and heat loss on the NOx formation in a post-flame region. In the flame region, NO is mainly produced by the Prompt NO mechanism including $N_2$O-intermediate NO mechanism over all equivalence ratios. However, thermal NO mechanism is more important than Prompt NO mechanism in the post-flame region. In the case of adiabatic condition, the increase of combustor length causes the remarkable increase of NO emission at the exit due to the increase of residence time. On the other hand, NO reaches the equilibrium state in the vicinity of flame region, considering radiation and conduction heat losses. Furthermore the NO, in the case of $\phi$=1.2, is gradually reduced in the downstream region as the heat loss is increased. From these results, it can be concluded that the controls of residence time and heat loss in a combustor should be recognized as an important NOx reduction technology.

DME/Air 비예혼합화염의 NOx 생성특성

황철홍,금성민,이창언,Hwang, Cheol-Hong,Kum, Sung-Min,Lee, Chang-Eon 대한기계학회 2007 대한기계학회논문집 Vol.31 No.11

The NOx emission characteristics of DME in laminar coaxial jet and counterflow nonpremixed flames were investigated using experimental and numerical approaches, respectively. The flame structure and NOx emission of DME were compared with those of $C_2H_6$ and $C_3H_8$. The DME flame was calculated using the Kaiser's mechanism, while the $C_2H_6$ and $C_3H_8$ flames were calculated using the $C_3$ mechanism. These mechanisms were combined with the modified Miller-Bowman mechanism for the analysis of NOx. Experimental results show in coaxial jet flame that DME flame has the characteristics of partial premixed flame and the flame length decreases up to 1/3 than that of $C_3H_8$ in the same condition of fuel mass flowrate. Then, the NOx emission of DME decreases to 40% approximately, comparing with that of $C_3H_8$. In the calculated results of counterflow nonpremixed flame, DME flame shows the $EI_{NO}$ decreases up to 50% approximately than those of$ C_2H_6$ and $C_3H_8$ flames when the equivalent fuels are consumed per unit mass and time. Although the overall NOx reaction path of DME is similar with other hydrocarbon fuels, it can be identified that DME flame has a distinct NO reduction mechanism due to the reburning NO chemistry in fuel rich region. From these results, we can conclude that the different NOx emission characteristics of DME flame with other hydrocarbon fuels are attributed to not the temperature increase and the activation of NO reactions due to O atom in DME fuel but the rapid processes of pyrolysis/oxidation.

층류 CH₄/Air 예혼합화염의 하류영역에서 NO 농도 예측을 위한 열손실 모델의 검토

황철홍,이창언,금성민,이기만,신명철,김세원,Hwang, Cheol-Hong,Lee, Chang-Eon,Kum, Sung-Min,Lee, Kee-Man,Shin, Myung-Chul,Kim, Se-Won 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.7

One-dimensional modeling of $CH_4$/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 ($h_{eff}$) of $1.0\;W/m^2K$ 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 ${\phi}\;{\geq}\;0.8$, the prompt NO mechanism plays an important role in the NO reduction under the adiabatic condition. On the other hand, the mechanism contributes to the NO production under the heat loss conditions.

하이브리드 촉매 연소기의 연소특성에 관한 수치적 연구

황철홍,정영식,이창언,Hwang, Cheol-Hong,Jeong, Yeong-Sik,Lee, Chang-Eon 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.4

The combustion characteristics of the hybrid catalytic(catalytic+thermal) combustor with a lean methane-air mixture on platinum catalyst were investigated numerically using a 2-D boundary layer model with detailed homogeneous and heterogeneous chemistries. for the more accurate calculations, the actual surface site density of monolith coated with platinum was decided by the comparison with experimental data. It was found that the homogeneous reactions in the monolith had little effect on the change of temperature profile, methane conversion rate and light off location. However, the radicals such as OH and CO were produced rapidly at exit by homogeneous reactions. The effect of operation conditions such as equivalence ratio, temperature, velocity, pressure and diameter of the monolith channel at the entrance were studied. In thermal combustor, the production of N$_2$O was more dominant than that of NO due to the relative importance of the reaction N$_2$+O(+M)→N$_2$O(+M). Finally the productions of CO and NOx by amount of methane addition were studied.

실용 연소장 해석을 위한 대 와동 모사

황철홍(Cheol-Hong Hwang),이창언(Chang-Eon Lee) 한국연소학회 2005 KOSCOSYMPOSIUM논문집 Vol.- No.-

층류 CH₄/Air 예혼합화염의 하류영역에서 NO 농도 예측을 위한 열손실 모델의 검토

황철홍(Cheol-Hong Hwang),이창언(Chang-Eon Lee),금성민(Sung-Min Kum),이기만(Kee-Man Lee),신명철(Myung-Chul Shin),김세원(Se-Won Kim) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.7

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/㎝). 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/㎡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/㎝) 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 ø≥0.8 , the prompt NO mechanism plays an important role in the NO reduction under the adiabatic condition. On the other hand, the mechanism contributes to the NO production under the heat loss conditions.

모형 가스터빈 연소기에서 선회 예혼합화염의 대와동모사(LES)

황철홍(Cheol-Hong Hwang),이창언(Chang-Eon Lee) 한국항공우주학회 2006 한국항공우주학회지 Vol.34 No.7

본 논문에서는 대와동모사를 이용하여 모형 가스터빈 연소기에서 난류 예혼합연소의 선회 유동구조와 화염특성이 검토되었다. 비정상 화염 거동을 모사하기 위하여 G-방정식 화염편 모델이 적용되었다. 결과로서, 입구 선회수 증가에 따른 코너 및 중앙 재순환 유동이 뚜렷한 차이를 보이며, 화염의 길이도 점차 감소됨을 확인 할 수 있었다. 또한 강선회 조건에서 역화현상의 원인이 확인되었다. 정확한 비정상 화염거동의 모사를 위하여, 연소실 내 음향파 거동의 예측성능이 우선적으로 검토되었으며, 스텝 모서리 근처에서 생성된 와동이 화염면 변동에 가장 큰 영향을 주고 있음을 알 수 있었다. 마지막으로 비정상 화염-와동 상호작용에 대한 해석을 통해 선회와 음향파의 전개로부터 생성된 와동의 진동이 화염면 및 열발생의 변동과 밀접하게 관련되어짐을 체계적으로 규명하였다. In the present paper, the swirl flow structure and flame characteristics of turbulent premixed combustion in a model gas turbine combustor are investigated using large eddy simulation(LES). A G-equation flamelet model is employed to simulate the unsteady flame behavior. When inlet swirl number is increased, the distinct flow structures, such as the shapes of corner recirculation and center toroidal recirculation zone, are observed and the flame length is shorted gradually. Also, the phenomena of flashback are identified at strong swirl intensity. In order to get the accurate description of unsteady flame behavior, the predictive ability of the acoustic wave in a combustor is primarily evaluated. It is found that the vortex generated near the edge of step plays an important role in the flame fluctuation. Finally it is examined systematically that the flame and heat release fluctuation are coupled strongly to the vortex shedding generated by swirl flow and acoustic wave propagation from the analysis of flame-vortex interaction.

DME/Air 비예혼합화염의 NOx 생성특성

황철홍(Cheol-Hong Hwang),이창언(Chang-Eon Lee),금성민(Sung-Min Kum) 대한기계학회 2007 大韓機械學會論文集B Vol.31 No.11

The NOx emission characteristics of DME in laminar coaxial jet and counterflow nonpremixed flames were investigated using experimental and numerical approaches, respectively. The flame structure and NOx emission of DME were compared with those of C₂H? and C₃H?. The DME flame was calculated using the Kaiser’s mechanism, while the C₂H? and C₃H? flames were calculated using the C₃ mechanism. These mechanisms were combined with the modified Miller-Bowman mechanism for the analysis of NOx. Experimental results show in coaxial jet flame that DME flame has the characteristics of partial premixed flame and the flame length decreases up to 1/3 than that of C₃H? in the same condition of fuel mass flowrate. Then, the NOx emission of DME decreases to 40% approximately, comparing with that of C₃H?. In the calculated results of counterflow nonpremixed flame, DME flame shows the EINO decreases up to 50% approximately than those of C₂H? and C₃H? flames when the equivalent fuels are consumed per unit mass and time. Although the overall NOx reaction path of DME is similar with other hydrocarbon fuels, it can be identified that DME flame has a distinct NO reduction mechanism due to the reburning NO chemistry in fuel rich region. From these results, we can conclude that the different NOx emission characteristics of DME flame with other hydrocarbon fuels are attributed to not the temperature increase and the activation of NO reactions due to O atom in DME fuel but the rapid processes of pyrolysis/oxidation.

완전혼합 반응기에서 CH₄/Air 예혼합화염의 열손실율에 따른 NOx 생성특성

황철홍(Hwang, Cheol-Hong),이기만(Lee, Kee-Man),금성민(Kum, Sung-Min) 한국산학기술학회 2009 한국산학기술학회논문지 Vol.10 No.7

완전혼합 반응기에서 외부로의 열손실이 CH₄/air 예혼합화염의 NOx 생성특성에 미치는 영향을 수치해석으로 검토하였다. 주요 결과로서, 단열조건에서 NOx는 체류시간에 따라 급격히 증가하는 반면에, 열손실이 고려될 때 열전 달 상수와 체류시간의 증가에 따라 NOx 저감현상이 뚜렷하게 발생하였다. 민감도 해석을 통해 열손실율이 증가함에 따라 Thermal NO 기구와 Re-burning NO 기구는 NOx 저감에 크게 기여하는 반면, Prompt NO 기구와 N2O-경유 NO 기구는 오히려 NOx 증가에 기여함을 확인하였다. NOx 생성기구는 열전달 상수 및 체류시간의 변화에 따라 매우 복 합한 특성을 갖지만, NOx 농도는 독립된 Thermal NO 기구에 의해 표현될 수 있었다. 이를 통해 실용 CH₄/air 예혼 합 연소기에서 NOx 농도를 예측할 수 있는 열손실율과 체류시간을 조합한 새로운 NOx 상관식이 도출되었다. The effect of heat loss rate on NOx formation of CH₄/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 N2O-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 CH₄/air premixed combustor.