• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.548-558
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• 1995

An experimental investigation has been conducted to study the spray and combustion characteristics using the air-assisted twin fluid atomizer. Axial mean and fluctuating velocity components as well as drop-size distributions in non-reaction spray were measured with a nonintrusive phase doppler technique. Droplet number density distributions were also visualized using high speed CCD camera. Locations of spray and flame boundaries are obtained by direct photographic method. It is confirmed that at the fixed fuel flow rate, the increase of the atomizing air flow causes improvements on both spray and combustion characteristics under stable flame conditions. Internal group combustion modes where flame is located inside the spray boundary are observed to exist in the upstream region of higher droplet number density.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.512-518
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• 1994

An experimental study is made on turbulent diffusion flames stabilized by a circular cylinder in a divergence flow. In this paper, stabilization characteristics and flame structure are examined by varying the divergence angle of duct and position of a circular cylinder. The fuel used is a commercial grade gaseous propane injected by two slit of rod. It is found that the positive pressure gradient greatly influences the eddy structure behind the rod. and that two different kinds of combustion patterns exist at the blowoff limit depending on the divergent angle of duct. They are distinguished by their wake structures: one associated with Karman vortex shedding, the other without it. Also, the blowoff velocity in the former is found to be higher than in the later.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.287-298
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• 2003

A numerical investigation of a catalytically stabilized thermal (CST) combustor was conducted for a multi-channel catalyst bed, and both the catalyst bed and thermal combustor were simultaneously modeled. The numerical model handled the coupling of the surface and gas reaction in the catalyst bed as well as the gas reaction in the thermal combustor. The behavior of the catalyst bed was investigated at a variety of operating conditions, and location of the flame in the CST combustor was investigated via an analysis of the distribution of CO concentration. Through parametric analyses of the flame position, it was possible to derive a criterion to determine whether the flame is present in the catalyst bed or the thermal combustor for a given inlet condition. The results showed that the maximum inlet temperature at which the flame is located in the thermal combustor increased with increasing inlet velocity.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.89-95
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• 2006

This study has numerically modelled the combustion processes of the turbulent swirling premixed lifted flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially-injected air jets induce the turbulent swirling flow which plays the crucial role to stabilize the turbulent lifted flame. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flamelet model. Two-dimensional and three-dimensional computations are made for the various swirl numbers and nozzle length. In terms of the centerline velocity profiles and flame liftoff heights, numerical results are compared with experimental data The three-dimensional approach yields the much better conformity with agreements with measurements without any analytic assumptions on the inlet swirl profiles, compared to the two-dimensional approach. Numerical clearly results indicate that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling stoichiometric and lean-premixed lifted flames in the low-swirl burner.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.6
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• pp.274-284
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• 1995

The effect of turbulence and ignition energy on flame kernel growth in mathanol-air mixtures has been studied in a constant volume vessel. Experiments were made under different turbulent intensity conditions, ignition energy and over a range of equivalence ratio. Characteristics of turbulent flow were grasped by measurments of gas pressure and visualization of flame propagation. Flow velocity was measured by use of hot wire anemometer. A comparison of the effect of turbulence on ignition probability and flame kernel volume variation ratio is also presented.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.193-196
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• 2015

Combustion of low concentration VOC in inert gas around the flammability limit has been experimentally studied. Streams of nitrogen and propane mixture with various compositions and flow conditions were treated by a turbulent partially-premixed pilot flame. HC and CO contents in exhaust gas measured and the flow patterns were visualized. The results suggested that there exists an optimal mixture velocity range for efficient combustion treatment for each flow condition and composition of the mixture.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.181-188
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• 2005

Large eddy simulation(LES) methodology used to model the isothermal swirling flows in a dump combustor and the turbulent premixed flame in a model gas turbine combustor. The LES solver was implemented on parallel computer consisting 16 processors. In isothermal flow simulation, the results was compared with that of ${\kappa}-{\varepsilon}$ model as well as experimental data, in order to verify the capability of LES code. To model the turbulent premixed flame in a gas turbine, the G-equation flamelet model was used. The results showd that LES and RANS well predicted the mean velocity field of a non-swirling flow. However, in swirling flow, LES showed a better performance in predicting the mean axial and azimuthal velocities, and the central recirculation zone than those of RANS. In a model gas turbine combustor, the operation condition of high pressure and temperature induced the different phenomena, such as flame length and flow-field information, comparing with the condition of ambient pressure and temperature. Finally, it was identified that the flame and heat release oscillations are related to the vortex shedding generated by swirl flow and pressure wave propagation.

• Journal of Power System Engineering
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• v.20 no.2
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• pp.32-42
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• 2016

Under part load condition of spark-ignition engine, pumping loss had great effect on engine efficiency. To reduce pumping loss, the study designed spark-ignited engines to make direct spray of gasoline to combustion chamber. In spark-ignited direct-injection engines, ignition probability is important for successful combustion and flame propagation characteristics are also different from pre-mixed combustion. This study designed a visualization testing device to study ignition probability of spark-ignited direct-injection LPG fuel and combustion flame characteristics. This visualization device consists of combustion chamber, fuel supply system, air supply system, electronic control system and data acquisition system. Ambient pressure, ambient temperature and ambient air flow velocity are important parameters on ignition probability of LPG-air mixture and flame propagation characteristics, and the study also found that sprayed LPG fuel can be directly ignited by spark-plug under proper ambient conditions. To all successful cases of ignition, the study recorded flame propagation image in digital method through ICCD camera and its flame propagation characteristics were analyzed.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.88-97
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• 2001

The present study numerically investigates the fuel-air mixing characteristics, flame structure, and pollutant emission inside a double-swirler combustor. A PSR(Perfectly Stirred Reactor) based microstructural model is employed to account for the effects of finite rate chemistry on the flame structure and NO formation. The turbulent combustion model is extended to nonadiabatic flame condition with radiation by introducing an enthalpy variable, and the radiative heat loss is calculated by a local, geometry-independent model. The effects of turbulent fluctuation are taken into account by the joint assumed PDFs. Numerical model is based on the non-orthogonal body-fitted coordinate system and the pressure/velocity coupling is handled by PISO algorithm in context with the finite volume formulation. The present PSR-based turbulent combustion model has been applied to analyze the highly intense turbulent nonpremixed flame field in the double swirler combustor. The detailed discussions were made for the flow structure, combustion effects on flow structure, flame structure, and emission characteristics in the highly intense turbulent swirling flame of the double swirler burner.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1234-1243
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• 1990

Double coaxial are jets(annular and coaxial air jets) between which propane gas is fed was selected to study the structure of diffusion flames in turbulent shear flow. Schlieren and direct photographs are taken to visualize the flame structure. Mean and fluctuating temperatures and ion currents were measured to investigate the macroscopic and the instantaneous flame structure. The objective of this study is to understand the interaction between combustion and mixing process especially in the transition region of turbulent shear flow. The investigation reported in this paper focuses on the macroscopic and the instantaneous structures of three flames obtained. The increased mixing effect resulting from increase of Reynolds number of central air jet makes the flame bluish and short. When the velocity of surrounding air stream is higher than that of central air jet, the instantaneous flame structure is composed of coherent structure. It is considered that the flame structure of transitional region of mixing layer depends on the structure of mixing layer of non-reacting conditions.