• Journal of the Korean Institute of Gas
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• v.14 no.3
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• pp.8-13
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• 2010

Hydrogen is expected to become a new, clean source of energy for the next generation. Therefore, many studies have investigated the characteristics of the hydrogen flame. However, because the hydrogen flame has high temperature, the flame does not emit visible light, and the flame propagates at a high velocity, investigating its characteristics is difficult. In the present study, in order to simultaneously examine the flame temperature and flame propagation velocity of hydrogen/air mixtures, ultra fine thermocouples with diameters of 12.7, 25.4, and 50.8 ${\mu}m$ are utilized. The results show that it is possible to detect the arrival time of the flame. Due to the temperature compensation with the time constants of thermocouples, it is also possible to estimate the flame temperature.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.75-81
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• 2012

Autoignited lifted flames in laminar jets with hydrogen-enriched methane fuels have been investigated experimentally in heated coflow air. The results showed that the autoignited lifted flame of the methane/hydrogen mixture, which had an initial temperature over 920 K, the threshold temperature for autoignition in methane jets, exhibited features typical of either a tribrachial edge or mild combustion depending on fuel mole fraction and the liftoff height increased with jet velocity. The liftoff height in the hydrogen-assisted autoignition regime was dependent on the square of the adiabatic ignition delay time for the addition of small amounts of hydrogen, as was the case for pure methane jets. When the initial temperature was below 920 K, where the methane fuel did not show autoignition behavior, the flame was autoignited by the addition of hydrogen, which is an ignition improver. The liftoff height demonstrated a unique feature in that it decreased nonlinearly as the jet velocity increased. The differential diffusion of hydrogen is expected to play a crucial role in the decrease in the liftoff height with increasing jet velocity.

• Journal of Energy Engineering
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• v.13 no.4
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• pp.311-318
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• 2004

In the present study, the combustion characteristics of methane and hydrogen-supplemented methane as alternative fuels for automotive vehicles were investigated at various hydrogen substitution rate, ignition position and ignition methods in a CVCC. The main results obtained from the study can be summarized as follow. In case of center ignition and neat methane-air mixture, the flame propagation processes are propagated with an elliptical shape, but they are changed an instable elliptical shape flame with very regular cells and higher velocity by increasing the hydrogen supplement rate. In case of side, 0.5R ignition and neat methane-air mixture, the flame propagation processes are propagated with an instable elliptical shape flame, but they are changed from an instable elliptical shape to wedge shape flame with very irregular cells and higher velocity by increasing the hydrogen supplement rate. Although the flame propagation shape with ignition position and ignition devices was not differ, the flame area of MSCDI device was a little larger than it of CDI device at the same time.

• 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 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.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.98.1-98.1
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• 2011

전 세계적으로 대표적인 대중교통으로 천연가스버스가 운행 중에 있으며, 천연가스의 저장을 위하여 대부분의 차량이 복합용기를 사용하고 있다. 또한 친환경자동차로 개발되고 있는 수소연료전지자동차도 수소 저장용으로 복합용기를 적용하여 상용화를 추진 중에 있다. 복합용기의 상용화가 증가하면서 복합용기의 안전성 확보가 가장 중요한 이슈가 되고 있다. 기체상태의 고압가스를 교통수단에 적용하기 위하여, 저장매체인 고압복합용기의 안전성 및 기술 확보를 위한 기술개발과 안전기준의 확립을 위한 기준개발이 미국, 유럽, 일본 등 다수의 국가에서 진행되고 있다. 현재 복합용기의 안전성을 확인하는 기준은 각 나라의 기준에 따라 진행되고 있으며 천연가스자동차용 저장용기 국제표준으로는 ISO 11439가 적용되고 있다. 수소연료전지자동차용 수소용기의 안전기준은 아직 확립되지 않은 상태이며, 개발된 초안으로는 국제규정으로 UN ECE R No.79 및 국제기술표준으로 ISO/TS 15869가 있다. 개발 중인 국제기준 및 국내기준에서 가장 취약한 부분이 화염시험이다. 화염시험은 자동차에 화재가 발생했을 경우 용기의 폭발을 막기 위하여 안전밸브가 정상적으로 작동하는 지를 확인하는 시험이다. 하지만 현재의 시험방법으로는 자동차에서 발생하는 국부적인 화염에 대한 안전성을 확인하기가 어려운 실정이다. 본 연구에서는 국내의 화염시험기준을 개발하기 위해 수행된 화염시험에 대한 결과와 화염시험장치를 제안하고자 한다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.780-787
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• 2019

As a carbon-free, green growth alternative, internal and external interest in hydrogen energy and technology is growing. Hydrogen was added to co-axial methane, methane-propane, and methane-propane-ethane diffusion flames, which are the main ingredients of LNG, to evaluate its effect on flame formation and combustion products. The variation in combustion products produced by adding hydrogen gradually to diffusion pyrolysis at room temperature and normal pressure conditions was observed experimentally by using a gas analyzer, and the shape of diffusion pyrolysis was observed step by step using a digital camera. The experimental results showed that the production volume of nitrogen oxides tended to increase and became close to linear as hydrogen was added to the diffusion pyrotechnic. This is because the relatively high temperature of heat insulation and fast combustion speed of hydrogen facilitated the production of thermal NOx. On the other hand, CO2 production tended to decrease as hydrogen was added to reduce the overall carbon ratio contained in the mixed diffusion flame of methane, methane-propane, and methane-ethane-propane. This means that the mixed fuel use of LNG-hydrogen in ships may potentially reduce emissions of CO2, a greenhouse gas.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.639-646
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• 2012

The characteristics of autoignited lifted flames in laminar jets of carbon monoxide/hydrogen fuels have been investigated experimentally in heated coflow air. In result, as the jet velocity increased, the blowoff was directly occurred from the nozzle-attached flame without experiencing a stabilized lifted flame, in the non-autoignited regime. In the autoignited regime, the autoignited lifted flame of carbon monoxide diluted by nitrogen was affected by the water vapor content in the compressed air oxidizer, as evidenced by the variation of the ignition delay time estimated by numerical calculation. In particular, in the autoignition regime at low temperatures with added hydrogen, the liftoff height of the autoignited lifted flames decreased and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between momentum and mass diffusion in fuel jets during the autoignition process.