• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.242-245
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• 2009

The effect of fuel composition on flame length was studied in a non-premixed turbulent diluted hydrogen jet with coaxial air. The observed flame length was expressed as a function of the ratio of coaxial air to fuel jet velocity and compared with a theoretical prediction based on the velocity ratio. Four cases of fuel mixed by volume were determined. In the present study, we derived a scaling correlation for predicting the flame length in a simple jet with coaxial air using the effective jet diameter in the near-field concept. The experimental results showed that visible flame length had a good relation with the theoretical prediction. The scaling analysis is also valid for diluted hydrogen jet flames with varied fuel composition.

• Proceedings of the KAIS Fall Conference
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• 2002.11a
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• pp.293-296
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• 2002

본 논문에서는 수소/액체연료/공기의 연소특성에 대해 CFD상용프로그램을 사용하여 수치해석을 수행하였다. 먼저 프로그램을 검증하기 위하여 수소/공기의 난류 비예혼합 화염에 대한 반응물과 생성물의 몰분율을 Barlow실험 결과와 비교하였고, X축 방향의 온도분포를 Flury의 실험 값과 비교하여 값이 물리적으로 근사함을 확인하였다. 혼합분율(Mixture Fraction)과 확률밀도함수(PDF)의 접근 방법을 이용하여 화염진단과 오염물질발생에 중요한 역할을 하는 중간 종들의 몰분율을 확인하였다. 수소/액체연료/공기에 대해서는 화염형성에 있어서 가장 중요한 연료와 산화제의 속도비 변화(100,10,1,0.1)로부터 산화제속도가 연료속도 보다 클 경우 고속 측인 산화제에 의해 연료의 확산이 지배되는 현상으로 인하여 화염의 온도분포가 최고가 됨을 확인하였다. 또한, 연소과정 중 발생하는 오염물질의 농도를 수치적으로 해석하여 최저의 오염농도를 가질 수 있는 속도 비를 찾아 낼 수 있었다. 수소/공기와 수소/액체연료/공기의 온도 장 비교를 통하여 수소/액체연료/공기의 혼합물이 대체에너지로서의 가능성을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.275-282
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• 2010

The effect of swirl flow on NOx in a nonpremixed turbulent hydrogen jet with coaxial air was studied. The swirl vane angle was varied from $30^{\circ}$ to $90^{\circ}$. The fuel jet air velocity and coaxial air velocity were varied in an attached flame region as $u_F=85{\sim}160m/s$ and $u_A=7{\sim}14m/s$. The objective of the current study was to analyze the characteristics of nitrous oxide emission in a swirl flow and to propose a new parameter for EINOx scaling. The experimental results show that EINOx decreases with the swirl vane angle and increased with flame length. Further, EINOx scaling factors can be determined by considering the effective diameter ($d_{F,eff}$) in a far field concept. The EINOx increased in proportion to the flame residence time (${\sim}{\tau_R}^{1/2.8}$) and the global strain rate (${\sim}{S_G}^{1/2.8}$).

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.393-396
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• 2008

The study of nitrogen dilution effect on flame stability was experimentally investigated in non-premixed turbulent lifted hydrogen jet with coaxial air. hydrogen gas was used as a fuel and coaxial air was injected to make flame liftoff. And both of the fuel jet and coaxial air velocity were fixed as $u_F$=200 m/s and $u_A$=16 m/s, while nitrogen diluents mole fraction was varied from 0 to 0.2. For the analysis of flame structure and flame stabilization mechanism, the simultaneous measurement of PIV/OH PLIF had been performed. It was found that the turbulent flame propagation velocity increased as decreasing of nitrogen mole fraction. We concluded that the turbulent flame propagation velocity was expressed as a function of turbulent intensity, even though the mole fraction of nitrogen diluents gas was changed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.4
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• pp.352-356
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• 2008

In this study of lifted hydrogen jet with coaxial air, we have experimentally studied the characteristics of stabilization point in turbulent diffusion flames. The objectives are to present the phenomenon of a liftoff height decreasing as increasing fuel velocity and to analyse the flame structure and behavior including liftoff mechanisms. The fuel jet exit velocity was changed from 100 up to 300 m/s and a coaxial air velocity was fixed at 16 m/s with a coflow air less than 0.1 m/s. For the simultaneous measurement of velocity field and reaction zone, PIV and OH PLIF technique was used with two Nd:Yag lasers and CCD cameras. It has been suggested that the stabilization of lifted hydrogen diffusion flames was correlated with a turbulent intensity, $S_t{\sim}u^{\prime}$, and jet Reynolds number, $S_t{\sim}Re^{0.017}_{jet}$.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.1-8
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• 2012

Acoustic-pressure response of diluted hydrogen-air diffusion flames is investigated numerically by adopting a fully unsteady analysis of flame structures in low and high pressure regimes. As acoustic frequency increases, finite-rate chemistry is enhanced through a nonlinear accumulation of heat release rate for any pressure regime, leading to a high amplification index. Same numerical results are analyzed with application of a pressure-sensitive time lag model, and thereby, interaction index and time lag are calculated for each pressure regime. The interaction index has the largest value in each pressure regime at an acoustic frequency near 1000 Hz. In a high-pressure regime, flames are more unstable than in a low-pressure regime. The interaction index shows a good agreement with the amplification index.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.1
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• pp.12-22
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• 2004

In order to evaluate the potential of partial hydrocarbon substitution to improve the safety of hydrogen use in general and the performance of internal combustion engines in particular, the outward propagation and development of surface cellular instability of spark-ignited spherical premixed flames of mixtures of hydrogen, hydrocarbon, and air were experimentally studied at NTP (normal temperature and pressure) condition in a constant-pressure combustion chamber. With propane being the substituent, the laminar burning velocities, the Markstein lengths, and the propensity of cell formation were experimentally determined, while the laminar burning velocities and the associated flame thicknesses were computed using a recent kinetic mechanism. Results show substantial reduction of laminar burning velocities with propane substitution, and support the potential of propane as a suppressant of both diffusional-thermal and hydrodynamic cellular instabilities in hydrogen-air flames.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.25-25
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• 1999

안정화 화염으로 수소 확산 화염을 이용한 메탄/공기 난류 예혼합 화염의 미연가스 영역의 난류 특성을 측정하였다. 측정은 동일한 위치에 대해서 화염이 존재할 때와 존재하지 않을 때에 대해 수행되었다. 버너 출구 레이놀즈 수 7000에서 당량비 0.6과 1.0의 경우에 대해 실험이 수행되었다. 난류 유동장은 2색 레이저 유속계에 의해 측정되었다. 21개의 위치에 대해서 반복적으로 측정이 수행되었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1158-1164
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• 2003

Steady-state structure and acoustic-pressure responses of $H_2$/Air counterflow diffusion flames are studied numerically with a detailed chemistry in view of acoustic instability. The Rayleigh criterion is adopted to judge acoustic amplification or attenuation from flame responses. Steady-state flame structures are first investigated and flame responses to various acoustic-pressure oscillations are numerically calculated in near-equilibrium and near-extinction regimes. The acoustic responses of $H_2$/Air flame show that the responses in near-extinction regime always contribute to acoustic amplification regardless of acoustic-oscillation frequency Flames near extinction condition are sensitive to pressure perturbation and thereby peculiar nonlinear responses occur, which could be a possible mechanism in generating the threshold phenomena observed in combustion chamber of propulsion systems.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.320-325
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• 2003

Acoustic-Pressure Response of diluted hydrogen-air diffusion flames is investigated numerically by adopting a fully unsteady analysis of flame structures. In the low-pressure regime, the amplification index remains low and constant at low frequencies. As acoustic frequency increases, finite-rate chemistry is enhanced through a nonlinear accumulation of heat release rate, leading to a high amplification index. Finally, the flame responses decrease at high frequency due to the response lag of the transport zone. For a medium-pressure operation and low-frequency excitation, the amplification index is low and constant. It then decreases at moderate frequencies. As frequency increases further, the amplification index increases appreciably due to an intense accumulation effect.