• 대한기계학회논문집B
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• 제22권2호
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• pp.193-204
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• 1998

Numerical analysis was performed with multicomponent transport properties and detailed reaction mechanisms for axisymmetric 2-D CH$_{4}$ jet diffusion flame. Calculations were carried out twice with the $C_{2}$-Thermal Mechanism including $C_{2}$ and thermal NO reactions and the $C_{2}$-Full Mechanism including prompt NO reactions in addition to the above $C_{2}$-Thermal NO mechanism. The results show that the flame structures such as flame temperature, major and minor species concentration are indifferent to respective mechanisms. The production path of Thermal NO is dominant comparing with that of Prompt NO in total NO production of pure CH$_{4}$ jet diffusion flame. This is because thermal NO mechanism mainly contributes to positive formation of NO in the whole flame region, but Prompt NO mechanism contributes to negative formation in the fuel rich region. In addition, 0$_{2}$ penetration near the nozzle outlet affects the flame structures, especially N0$_{2}$ formation characteristics.

• 대한기계학회논문집B
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• 제31권11호
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• pp.926-935
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• 2007

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.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1997년도 제15회 KOSCO SYMPOSIUM 논문집
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• pp.61-68
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• 1997

The morphology and size distribution of chromium oxides and the concentration measurement of atomic arsenic have been studied in laminar diffusion flames. Nitrogen was added to vary flame temperatures in hydrogen flames. Ethene flames were used in order to investigate the potential for interaction between the soot aerosol that is formed in these flames and the chromium aerosol. Two sources of chromium compounds were introduced: chromium nitrate and chromium hexacarbonyl. A detailed investigation of the morphology was carried out by scanning electron microscopy (SEM). The amounts of Cr(VI) and total Cr were determined by a spectrophotometric method and by X-ray fluorescence spectrometry, respectively. Also, LIF was used for the measurement of atomic arsenic, which was excited at 197.2 nm and was detected at 249.6 nm. Results showed that the morphology of the particles varied with the flame temperature and with the chromium source. The particles were characterized by porous structures, cenospheres and agglomerated dense particles when chromium nitrate solution was added to the flames. At low to moderate temperatures, porous sintered cenospheric structures were formed, in some cases with a blow hole. At higher temperatures, an agglomerated cluster which was composed of loosely sintered submicron particles was observed. It was also found that the emission of Cr(VI) from the undiluted $H_2$ flame was more than 10 times larger than in the 50% $H_2$ / 50% $N_2$ flame on a mass basis. Single point LIF measurement of atomic arsenic indicated that arsenic exist only in the low temperature, fuel rich region.

• 대한기계학회논문집B
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• 제25권2호
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• pp.147-155
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• 2001

Experimental investigations were conducted for two hydrogen-nitrogen coaxial jet diffusion flames. A flame was a conventional coaxial jet diffusion flame and the other was a coaxial jet diffusion flame of which ambient air-jet turbulence was intensified. In this study, firstly two kinds of NOx measuring system were campared by using different convertors, secondly the NOx formation characteristics were investigated in order to examine the effect of turbulence intensity. In this study it is known that stainless convertor has some problem in the converting process from NO$_2$to NO in fuel rich region but molybdenum convertor can detect the amount of NOx correctly. The increase of turbulence intensity reduces the thermal NOx less than a half in our experiment and this effect is conspicuous near the nozzle. The conversion rate from NO to NO$_2$and the portion of NO$_2$among NOx are increased with turbulence intensity. These NOx measurements will help to understand the influences of turbulence intensity on NOx formation.

• 한국자동차공학회논문집
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• 제7권8호
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• pp.43-54
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• 1999

The effects of equivalence ratio and pressure on burnt gas temperature in premixed fuel rich propane-oxygen-inert gas combustion are investigated over the wide ranges of equivalence ration from 1.5 to 2.7 and pressure from 0.1 to 7 MPa by using a specially designed disk -type constant-voume combustion chamber, The premixtures are simultaneously ignited by eight spark plugs located on the circumference of combustion chamber with 45 degree interals. The eight converging flames compress the end gases to high pressures. The burnt gas temperature is meausured by the nmodifie dtow-colr pyrometry method. The transmissivity in the chamber center during the final stage of combustion at the hightest pressure is meausred by in situ laser extinction method. It is found that a temperature difference between the burnt gas temperature measured by mofidied and conventrational two-color method is 10 to 20 K, but the accuracy of the modified two-color methdo is higher if the local transmissivity in observed region is uniform , and the combustion at higher pressures results gas density conditions and the burnt gas temperature increases as the volume fraction of argon is increased because the specific heat of argon is lower compared to that of nitrogen with a constant equivalence ratio.

• 한국추진공학회지
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• 제21권1호
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• pp.63-71
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• 2017

메탄($CH_4$)/산소($O_2$) 액체이원추진제는 친환경성, 무독성, 경제성, 우수한 성능 등의 장점으로 최근 들어 차세대 친환경 이원추진제로서 관심을 받고 있다. 본 연구에서는 연소실 내 압력 변화에 따른 기체 메탄/산소 비예혼합 동축 화염의 연소안정한계를 측정하고, 화염 및 유동의 가시화를 통해 분사 조건 및 압력 변화에 따른 화염의 구조와 특성을 파악하였다. 연구 결과 연료과농 조건에서 연소실 내 압력이 증가할 경우 연소안정한계가 확장되고 반응 영역이 증가하는 것을 확인할 수 있었다.

• 새물리
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• 제68권11호
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• pp.1173-1182
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• 2018

메조포러스 실리카는 강한 친수성과 구조적인 특성으로 인하여 저습환경에서도 이온교환막에 적절한 수화가 일어나도록 할 것이다. 그러므로 메조포러스 실리카와 나피온을 합성한 이온교환막은 낮은 상대습도에서도 우수한 양성자 전도도를 보일 것이다. 메조포러스 실리카와 나피온 합성이온교환막의 이온채널형성 그리고 네트워크를 통한 양성자 이동에 대한 이해는 합성이온교환막을 개발하고 최적화하기 위해 필수적이라 할 수 있다. 이 연구에서는 메조포러스 구조 (mesoporous cellular foam) $SiO_2/Nafion$ 합성이온교환막을 제작하고 양성자 전도도 및 성능을 평가하였다. 또한, 정전기력 현미경(electrostatic force microscopy, EFM)을 사용하여 메조포러스 구조 $SiO_2/Nafion$ 합성 이온교환막의 표면 전하 밀도 측정을 통한 이온 채널의 분포 및 밀도를 분석하였다. 연구는 몇 가지 주목할 만한 결과를 보여주었다. 첫째, 합성이온교환막은 저습환경에서 우수한 양성자 전도도 및 성능을 나타내었다. 둘째, 합성이온교환막은 국부적으로 이온채널의 밀도가 주목할 만하게 높은 지역이 형성되며 동시에 양성자 전도도가 극단적으로 낮은 지역 또한 동시에 형성됨을 확인하였다.

• 한국재료학회지
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• 제34권7호
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• pp.330-340
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• 2024

Al-Mg-Si alloys are light weight and have excellent corrosion resistance, and are attracting attention as a liner material for high-pressure hydrogen containers in hydrogen fuel cell vehicles. Because it has excellent plastic hardening properties, it is also applied to car body panel materials, but it is moderate in strength, so research to improve the strength by adding Si-rich or Cu is in progress. So far, the authors have conducted research on the intergranular fracture of alloys with excessive Si addition from the macroscopic mechanical point of view, such as specimen shape. To evaluate their impact tensile properties, the split-Hopkinson bar impact test was performed using thin plate specimens of coarse and fine grain alloys of Al-Mg-X (X = Cr,Si) alloy. The effect of the shape of the specimen on the characteristics was studied through finite element method (FEM) analysis. As a result, it was found that the intergranular fracture of the alloy with excessive Si depended on the specimen width (W)/grain size (d), which can be expressed by the specimen size and grain size. As W/d decreases, the intergranular fracture transforms into a transgranular fracture. As the strain rate increases, the fracture elongation decreases, and the fracture surface of the intergranular fracture becomes more brittle. It was confirmed that intergranular fracture occurred in the high strain rate region even in materials with small grain sizes.