• 대한기계학회논문집
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• 제19권11호
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• pp.2981-2994
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• 1995

In order to elucidate the effects of positive pressure gradient on flame properties, structure and stabilization, an experimental study is made on turbulent diffusion flame stabilized by a circular cylinder in a divergent duct flow. A commercial grade gaseous propane is injected from two slits on the rod as fuel. In this paper, stabilization, characteristics and flame structure are examined by varying the divergent angle of duct. Temperature, ion current and Schlieren photographs were measured. It is found that critical divergent angle is expected to be about 8 ~ 12 degree through blow-off velocity pattern to divergent angle and the positive pressure gradient influences the flame temperature, intensity of ion current and eddy structure behind the rod. With the increase of divergent angle, typical temperature of recirculation zone is low but intensity of ion current is high in shear layer behind rod. Energy distributions of fluctuating temperature and ion current signals turn up low frequency corresponding to large scale eddies but high frequency corresponding to small scale eddies as well as low with the increase of divergent angle. Therefore the flame structure becomes a typical distributed-reacting flame.

• Journal of Advanced Marine Engineering and Technology
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• 제18권1호
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• pp.81-91
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• 1994

Combustion noise involved with chemical heat release and turbulent process in turbopropulsion systems, gasturbine, industrial furnaces and internal engines is indeed noisy. The experimental study reported in this paper is made to identify a dominant combustion noise in jet flames. Gaseous propane and kerosene fuel have been used with air as the oxidizer in a different jet combustion systems. Combustion and aerodynamic noise are studied through far field sound pressure measurements in an anechoic chamber. And also mean temperature and velocities and turbulent intensities of both isothermal and reacting flow fields were measured. It is shown that axial mean velocity of reacting flow fields is higher about 1 to 3m/sec than that of cold flow in a gaseous combustor. As the gaseous fuel flow rate increases, the acoustic power increases. But the sound pressure level for the spray flame decreases with increasing equivalence ratio. The influence of temperature in the combustion fields due to chemical heat release has been observed to be a dominant noise source in the spray flame. The spectra of combustion noise in gaseous propane and kerosene jet flame show a predominantly low frequency and a broadband nature as compared with the noise characteristics in an isothermal air jet.

• 대한기계학회논문집B
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• 제32권3호
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• pp.190-197
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• 2008

It was experimentally studied that the stabilization mechanism of turbulent, lifted jet flames in a non-premixed condition to reveal the newly found liftoff height behavior of hydrogen jet. The objectives are to report the phenomenon of a liftoff height decreasing as increasing fuel velocity, to analyse the flame structure and behavior of the lifted jet, and to explain the mechanisms of flame stability in hydrogen turbulent non-premixed jet flames. The hydrogen jet velocity was changed from 100 to 300m/s and a coaxial air velocity was fixed at 16m/s with a coflow air less than 0.1m/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. As a result, it was found that the stabilization of lifted hydrogen diffusion flames is correlated with a turbulent intensity and Karlovitz number.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.18-21
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• 2006

This paper investigates LES of turbulent combustion flow based on 2-scalar flamelet approach, where a G-equation and a conserved scalar equation simulate a propagation of premixed flame and a diffusion combustion process, respectively. The turbulent SGS modeling on these flamelet combustion approach is also researched. These LES models are applied to an industrial flows in a full scale gasturbine combustor with premixed and non-premixed flames. The numerical results predict the characteristics of experiment temperature profiles. Unsteady features of complex flames in combustor are also visualized.

• 대한기계학회논문집
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• 제18권5호
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• pp.1253-1263
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• 1994

The experimental study is carried out to identify the combustion generated noise mechanism in free turbulent jet diffusion flames. Axial mean fluctuating velocities in cold and reacting flow fields were measured using hot-wire anemometer and LDv.The overall sound pressure level and their spectral distribution in far field with and without combustion were also measured in an anechoic chamber. The axial mean velocity is 10-25% faster and turbulent intensities are about 10 to 15% smaller near active reacting zone than those in nonreacting flow fields. And sound pressure level is about 10-20% higher in reacting flow fields. It is also shown that the spectra of the combustion noise has lower frequency characteristics over a broadband spectrum. These results indicate that the combustion noise characteristics in jet diffusion flames are dominated by energy containing large scale eddies and the combusting flow field itself. Scaling laws correlating the gas velocity and heat of combustion show that the acoustic power of the combustion noise is linearly proportional to the 3.8th power of the mean axial velocity rather than 8th power in nonreacting flow fields, and the SPL increases linearly with logarithmic 1/2th power of the heat of combustion.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2326-2336
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• 1996

So most practical combustor is considered to the swirl flame, it is very important to examinate swirl flame structure and combustion characteristics. Recently, attention has been paid to the flame diagnostic by radical luminous intensity. For swirl flame structure and combustion characteristic, reverse flow boundary, temperature, ion current and radical luminous intensity were measured in the double-coaxial swirl combustor which was used principle of multi-annular combustor. This study had three experimental condition, S-type, C-type, SC-type. S-type and C-type flames were formed recirculation zone, but SC-type flame wasn't formed. C-type flame had two recirculation zone. The position with maximum value of ion current and CH-radical, temperature and OH-radical had similarity distribution almost. Therefore, it is possible that the macro structure of flame was measured by radical luminous intensity in the high intensity of turbulent combustion field which was formed by swirl.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.255-260
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• 2003

Characteristics of methane jet diffusion flames using pure oxygen with recirculating $CO_{2}$ as an oxidizer were investigated experimentally. A coflow burner was considered, and the diameter of confinement was larger than that of the coflow. No stabilized flame could be observed over 75% of $CO_{2}$ volume percent. A comparison between air and $O_{2}/CO_{2}$ mixture was made in terms of liftoff velocity, flame liftoff height, and blowout conditions. As results, more stable flame could be observed with $O_{2}/CO_{2}$ mixture for the case of having similar flame temperature.

• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.65-74
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• 2003

Air pollution included Nitric Oxide(NOx) from heating boilers is increased by pursuing better life. Development of low NOx emission boiler is strongly needed. However commercial burner for heating boiler is also asked to be thermal efficient and low-cost manufactuable in addition to low NOx emission. Small space for combustor including burner is usually allowed. In this study, parametric study of compact low NOx burner for heating boiler was done using numerical analysis and experiments. Commerical computational fluid dynamic(CFD) program named CFX 5-6 was used for numerical analysis of low NOx burner using turbulent diffusion flame. Comparison of outlet NO and outlet temperature under various equivalence ratio and fuel flow rate was performed between experiment and numerical analysis.

• 대한기계학회논문집
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• 제18권2호
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• pp.492-501
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• 1994

This study is an analysis of the turbulent diffusion flame with swirl flow and the calculated results are compared with experimental data in case of various swirl numbers and air-fuel rations. The mathematical model is restricted to single-phase, diffusion controlled combustion with swirl flow. Values of local flow properties were obtained by solving appropriate differential equation for continuity, momentum, stagnation enthalpy, concentration, turbulence energy, dissipation rate of turbulence energy, and the mean square of concentration fluctuation. The method is proposed for calculating the local probability of chemical reaction based on the use of the probability density function for the mixture fraction.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.775-778
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• 2007

The present study numerically investigate the detailed structure of the syngas diffusion flames. In order to realistically represent the turbulence-chemistry interaction, the transient flamelet model has been applied to simulate the combustion processes and $NO_X$ formation in the syngas turbulent nonpremixed flames. The single mixture fraction formulation is extended to account for the effects of the secondary inlet mixture. Computations are the wide range of syngas compositions and oxidizer dilutions. Based on numerical results, the detailed discussion has been made for the effects of syngas composition and oxidizer dilution on the structure of the syngas-air and syngas-oxygen turbulent nonpremixed flames.