• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.11-20
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• 1999

Acoustic pressure response and NO formation of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such non-monotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. Acoustic pressure response in each regime is investigated based on the Rayleigh criterion. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted. Emission index of NO shows similar behaviors as to the peak-temperature variation with pressure.

• 대한기계학회논문집B
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• 제36권8호
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• pp.857-864
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• 2012

복사열손실을 받는 확산화염의 선형 안정성 해석을 수행하여 복사강도와 Damkohler 수에 대한 화염 불안정이 나타나는 조건을 확인하였다. 대향류 유동장을 모델로 하여 Lewis 수는 1로 가정하였다. 반응속도 제한에 의한 소염근처에서 교란의 증가율은 실수의 고유값을 가지며 안정한계는 정상상태 소염조건과 정확하게 일치한다. 반면에 복사 열손실에 의한 소염 영역 근처에서 증가율의 고유값은 복소수이며 정상상태 소염 전에 맥동 불안정성이 예측된다. 진동하는 화염온도가 양의 실수 고유값을 갖는 정상상태 화염온도 보다 클 경우에만 한계 순환 안정 특성이 나타난다. 만약 그 온도보다 작게 되면 화염은 회복되지 못하고 소염된다. 넓은 복사강도 범위에 대하여 복사 열손실에 의한 불안정성의 안정한계 곡선을 도시하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.159-162
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• 2012

Combustion in a narrow space has been interested as a model of meso-scale combustors (or micro-combustors). Premixed flames have been used to overcome flame quenching in a narrow space and non-premixed flames have been used to improve flame stabilization. In this study, overall characteristics of premixed flame and non-premixed flame in narrow combustion spaces were reviewed. Various effects such as the flow velocity distribution, thermal interaction, enhanced mass diffusion were discussed and an eventual structure of the flame at the extinction limit was introduced.

• 동력기계공학회지
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• 제2권2호
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• pp.13-19
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• 1998

The purpose of study is to investigate the flame stability and Structure of turbulent diffusion flame behind the hollowed flame holder, which is located on the waste gas coming out from the test furnace. Fluctuating temperature and ion current measurement and their statistical treatment were used for the purpose. Three types of flame were stabilized and each of which were changed by adequate equivalence ration. And we found that have no periodicity near reacting zone.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.113-122
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• 2000

Dynamic structures of unsteady $CH_4$/Air jet diffusion flames with flame-vortex interaction were numerically investigated. A time-dependent, axisymmetric computational model was adopted for this calculation. Two step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including gravitational effect show that the large outer vortices and the small inner vortex street can be well simulated without any additional disturbances in the downstream of nozzle tip. It was found that the temperature and species concentrations had various values for the same mixture fraction in flame-vortex interaction region. This unsteady jet flame configuration accompanying flame-vortex interaction is expected to give good implications for the structure of turbulent flames.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.118-123
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• 2004

The combustion characteristics of 0.03MW turbulent methane/oxygen diffusion flames have been investigated to give basic informations for designing industrial oxyfuel combustors. NOx reduction has become one of the most determining factors in the combustor design since 3-5% nitrogen is intrinsically included from the current oxygen producing processes. Flame lengths and NOx concentrations were measured by varying flow velocities with and without installing quarls. Flame stabilities are significantly enhanced by oxyfuel combustion in contrast to air-fuel combustion. Flame length decreases with increasing fuel or oxygen velocity because of the enhancement of turbulent mixing. NOx concentration was reduced with increasing flo velocities. This can be attributed to the entrainment of inert product gases into flame decreasing flame temperature. The installation of quarl on the burners rather increased NOx concentration since the quarl blocked the entrainment above the nozzles.

• 한국연소학회지
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• 제7권1호
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• pp.8-14
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• 2002

Measurements of global emissions, flame radiation and flame dimensions are presented for unconfined turbulent-jet and precessing-jet diffusion flames. Precessing jet flames are characterised by increases in global flame radiation and global flame residence time for methane and propane fuels, however a strong dependency of the NOx emission indices on the fuel type exists. The fuel type dependence is considered to be because soot radiation is more effective than gas-radiation at reducing global flame temperatures relative to adiabatic flame temperatures and reducing the NO production rate.

• 동력기계공학회지
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• 제3권3호
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• pp.29-35
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• 1999

The purpose of study is to investigate the flame stability and structure of turbulent diffusion flame behind the hollowed flame holder, which is located on the waste gas coming out from the test furnace. PDFs and Power Spectra technique of fluctuating temperature and ion current measurement were needed for this purpose. We discussed that the three types of stabilized flames were found as the result of post study. In this paper, we established the stability mechanism near the flame holder.

• 대한기계학회논문집
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• 제16권9호
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• pp.1796-1804
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• 1992

본 연구에서는 동심확산화염내에 생기는 매연 입자의 크기와 농도를 광산란 소멸법으로 보다 정확히 측정하여 궁극적 목적인 매연입자 제어의 기반을 조성하고자 한다.

• 대한기계학회논문집
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• 제10권2호
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• pp.232-240
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• 1986

본 연구에서는 대향류 유동장에서 두 예혼합화염의 후류 상호작용을 Fig.1 과 같은 계를 이용하여 일반적인 Lewis수에 대하여 접합 점근 전개 방법으로 해석하 여, 강한 상호작용을 나타내는 구간의 변화가 확산선호도의 영향임을 규명하고, 화염 스트레치가 상호 작용하는 예혼합화염의 소화특성에 미치는 영향을 파악하였다.