• 한국자동차공학회논문집
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• 제13권2호
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• pp.170-177
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• 2005

The fuel-lean premixed flame has been considered one of the most efficient ways to reduce $NO_X$ emission during a combustion process. However, it is difficult to achieve stable fuel-lean premixed flames over the wide range of equivalence ratios: therefore, the application of fuel-lean flames to a practical combustion system is rather limited. In this study, the stability characteristics of fuel-lean flames stabilized by fuel-rich flames are investigated experimentally using a slot burner as a part of the basic research for practical application such as lean burn engines. Spontaneous emission of radical species were examined to understand the stability mechanisms of rich-lean premixed flames. The presence of fuel-rich flames could significantly lower the lean limit of fuel-lean flames. The stability of a fuel-lean flame is enhanced with the increase of fuel flow rate in a fuel-rich flame; how ever, it is not sensitive to the equivalence ratio of fuel-rich flames in the range of 1.2-2.4. The mechanisms of stable rich-lean premixed flames could be understood based on the characteristics of triple flame.

• BMB Reports
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• 제35권5호
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• pp.488-493
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• 2002

IgY was separated from a hen's egg yolk that was immunized with Helicobacter pyroli. The anti-H. pyroli IgY activity at acidic pH and the suppressive effect of polyol on acid-induced inactivation of IgY were investigated. Sorbitol and xylitol were used as polyols. IgY was quite stable at pH 5~7. Irreversible inactivation of IgY was observed at pH below 4, and proceeded rapidly at pH below 3. The acid stability of IgY was enhanced in the presence of 30% sorbitol or above. In a 50% aqueous sorbitol solution, an acid-induced inactivation was almost completely suppressed at pH 3. However, the improvement of IgY activity was not observed in the aqueous xylitol solution. IgY showed almost the same activity as native IgY when sucrose was substituted for sorbitol. On the other hand, the xylitol replacement with sucrose did not enhance the acid stability of IgY. The acid-induced inactivation of IgY was related to tryptophyl fluorescence. Fluorescence emission spectra suggested that structural changes near the tryptophan residues may occur under acidic conditions. An increase in sorbitol concentration induced a blue shift. The fluorescence emission of IgY in a 50% sorbitol solution had a peak at 330 nm, which was the same emission peak that was exhibited by native IgY. Sorbitol could, therefore, be used as a good stabilizer of IgY under acidic conditions.

• 한국수소및신에너지학회논문집
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• 제18권1호
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• pp.75-84
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• 2007

The effects of hydrogen enrichment to methane on NOx formation have been investigated with swirl stabilized pre-mixed hydrogen enriched methane flame in a laboratory-scale pre-mixed combustor(nominally of 5,000 kcal/hr). The hydrogen enriched methane fuel and air were mixed in a pre-mixer and introduced to the combustor through different degrees of swirl vanes. The flame stability was examined for different amount of hydrogen addition to the methane fuel, different combustion air flow rates and swirl strengths by comparing equivalence ratio at the lean flame limit. The hydrogen addition effects and swirl intensity on the combustion characteristics of pre-mixed methane flames were examined using gas analyzers, and OH chemiluminescence techniques to provide information about species concentration of emission gases and flowfield. The results of NOx and CO emissions were compared with a diffusion flame type combustor. The results show that the lean stability limit depends on the amount of hydrogen addition and the swirl intensity. The lean stability limit is extended by hydrogen addition, and is reduced for higher swirl intensity at lower equivalence ratio. The addition of hydrogen increases the NOx emission, however, this effect can be reduced by increasing either the excess air or swirl intensity. The NOx emission of hydrogen enriched methane premixed flame was lower than the corresponding diffusion flame under the fuel lean condition.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.140-147
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• 2000

Using lobed burner, flame visualization and measurements of NOx and CO concentration in the combustor exit were carried out to evaluate the relation between the lobed structure in a burner and pollutant emission characteristics. The flame stability is enhanced by the lobed burner compared to conventional circular one. The correlation on fuel discharge velocity for flame blowout should be included on a variable related to the wall effect of the burner, because the flame blowout is observed at the burner having large perimeter. The burner having lobed structure in fuel discharge side compared to conventional burner reduces by 5% NOx emission due to lower flame intensity through flame elongation. Meanwhile the burner having lobed structure in air discharge side and both fuel and air discharge side increase the NOx emission.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.II
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• pp.1096-1099
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• 2005

Multi-walled carbon nanotubes (CNTs) grown on catalyst dots by thermal chemical vapor deposition were vertically aligned with a high population density. Such densely populated CNTs showed poor field emission characteristics due to the electrical screening effect. We reduced the number density of CNTs using an adhesive tape treatment. For dotpatterned CNTs, the tape treatment decreased the CNT density by three orders of magnitude, drastically improved the turn-on electric field from 4.8 to $1.8V/{\mu}m$, and changed the emission image from spotty to uniform luminescence. We also report long-term emission stability of dot-patterned CNTs by measuring the emission currents with time at different duty ratios.

• Journal of Korean Vacuum Science & Technology
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• 제3권1호
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• pp.49-53
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• 1999

We have studied the field emission characteristics of diamond-like-carbon (DLC) films deposited by a layer-by-layer technique using plasma enhanced chemical vapor deposition, in which the deposition of a thin layer of DLC and a CH4 plasma exposure on its surface were carried out alternatively. The hydrogen-free DLC can be deposited by CH4 plasma exposure for 140 sec on a 5 nm DLC layer. N2 gas-phase doping in the CH4 plasma was also carried out to reduce the work function of the DLC. The optimum [N2]/[CH4] flow rate ratio was found to be 9% for the efficient electron emission, at which the onset-field was 7.2 V/$\mu\textrm{m}$. It was found that the hydrogen-free DLC has a stable electron emitting property.

• 한국표면공학회지
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• 제29권5호
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• pp.505-511
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• 1996

The field emission characteristics of diamond films deposited by microwave plasma enhanced chemical vapor deposition (MPECVD) method were investigated. Diamond films were deposited on n-type Si(100) wafer using various mixtures of hydrogen and methane gas, and the I-V characteristics are measured. We observed that the field emission characteristics depend on the $CH_4$ concentration and the diamond film thickness. All the films show remarkable emission characteristics; low turn-on voltage, high emission current density at lower voltage, uniform stable current density, and good stability and reproducibility. The threshold field for producing a current density of 1mA/$\textrm{cm}^2$ is found as low as 7.6V/$\mu\textrm{m}$.

• 한국표면공학회지
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• 제37권6호
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• pp.313-318
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• 2004

Vertically-aligned and uniformly-distributed CuO nanowires were formed on copper-coated Si substrates by wet chemical process, immersing them in a hot alkaline solution. The effects of hydrogen plasma treatment on the field emission characteristics of CuO nanowires were investigated. It was found that hydrogen plasma treatment enhanced the field emission properties of CuO nanowires by showing a decrease in turn-on voltage, and an increase in emission current density, and stability of current-voltage curves. However, the excessive hydrogen plasma treatment made the I-V curves unstable. It was confirmed by XPS (X-ray Photoelectron Spectroscopy) analysis that hydrogen plasma treatment deoxidized CuO nanowires, thereby the work function of the nanowires decreased from 4.35 eV (CuO) to 4.1 eV (Cu). It is thought that the decrease in the work function enhanced the field emission characteristics. It is well-known that the lower the work function, the better the field emission characteristics. The results suggest that the hydrogen plasma treatment is very effective in achieving enhanced field emission properties of the CuO nanowires, and there may exist an optimal hydrogen plasma treatment condition.

• 한국진공학회지
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• 제17권6호
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• pp.566-575
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• 2008

촉매 화학기상증착법을 이용하여 합성된 이중층 탄소나노튜브를 가지고 전계전자 방출원을 제작하여 이들의 신뢰성 있는 전계전자 방출특성을 조사하였다. 합성된 탄소 필라멘트들은 TEM, TGA, 그리고 Raman 분석을 통하여 결함이 없고 순도가 높은 이중층 탄소나노튜브가 합성이 되었음을 확인하였다. 이들 이중층 탄소나노튜브 전계전자 방출원은 이전극 구조에서 낮은 턴-온 전계와 높은 전류밀도의 전계전자 방출 특성을 보여주었고, 균질한 전계방출 패턴과 좋은 전계방출 안정성을 나타내었다.

• 한국항공우주학회지
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• 제40권11호
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• pp.1004-1009
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• 2012

탄소나노튜브는 우수한 전기적 특성과 전계를 집중시킬 수 있는 높은 종횡비 그리고 뛰어난 열적 안정성 때문에, 높은 전류밀도와 낮은 구동전압 그리고 긴 수명시간과 같은 우수한 전계 방출 특성을 구현할 수 있는 재료이다. 탄소나노튜브를 이용하여 전계방출원을 제작하기 위해서는 금속전극에 탄소나노튜브를 고정시켜야 한다. 이때 금속과 탄소나노튜브 사이의 접촉문제가 필수적인데, 본 실험에서는 그래핀을 계면으로 사용함으로써 본 문제를 해결하였다. 이러한 시도는 금속과 탄소나노튜브 사이에 우수한 전기적 열적 계면을 형성함으로써 기존 전계방출원보다 뛰어난 전계방출 성능을 얻을 수 있게 하였다. 본 연구를 통해 탄소나노튜브 전계방출원을 전자 추진원으로의 응용이 기대된다.