• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.287-289
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• 2015

Meso-scale combustion is defined as combustion phenomena within limited characteristic length scales that are comparable with the laminar flame length scales. In the laminar flame theory, four representative length scales have been involved; i.e., a reaction layer thickness, a thermal layer thickness, a quenching distance, and a Markstein length. When the effects of these length scales on the flame characteristics are understood, the laminar flame theories can be clarified. Therefore, a study on the meso-scale combustion phenomena should not be thought as just a specific phenomena occurring in an exceptional combustion condition. Instead, all combustion phenomena within meso-scale spaces need to be explained by our knowledge. During this challenge, our understanding on laminar flame structures can be extended. Considering that most turbulent combustion phenomena in engineering application are still have local laminar flame structures, studies on laminar flame structures need to be re-visited especially in academic aspects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1040-1049
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• 1996

The high loading combustion is accomplished by making the turbulent intensity strong and the scale small in the premixed combustor. The Da-mkoler number, which is decreased by short turbulent characteristic time or by long chemical reaction time, can make the distributed reaction flame. So we developed a doubled jet burner for high loading combustion. The doubled jet burner was designed to make the scale of the flame small by the effect of impingement and increasing shear stress with doubled jet. We investigated the turbulence characteristics of unburned mixture and visualized several flames with the typical schlieren photography. Then we studied the influence of several factors that related the scale of flame. Consequently, the doubled jet burner can make the eddy very small. And we can obtain the detail information of the flame scale through ADSF(the Average Distance between Successive Fringes) in the micro- schlieren photography. The ADSF is not a exact flame scale, but it has qualitative trend with increasing turbulent intensity. The ADSF is diminished remarkably with increasing turbulent intensity. The reason is that strong turbulent intensity makes the flame zone thick and flamelets numerous. We can confirm this fact by the signal analysis of ion currents.

• Journal of the Korean Society of Combustion
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• v.21 no.4
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• pp.6-15
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• 2016

The oxygen fuel MILD (Moderate or Intense Low-oxygen Dilution) combustion has been considered as one of the promising combustion technology for flame stability, high thermal efficiency, low emissions and improved productivity. In this paper, the effect of oxygen and fuel injection condition on formation of MILD combustion was analyzed using lab scale oxygen fuel MILD combustion furnace. The results show that the flame mode was changed from a diffusion flame mode to a split flame mode via a MILD combustion flame mode with increasing the oxygen flow rate. A high degree of temperature uniformity was achieved using optimized combination of fuel and oxygen injection configuration without the need for external oxygen preheating. In particular, the MILD combustion flame was found to be very stable and constant flame temperature region at 7 KW heating rate and oxygen flow rate 75-80 l/min.

• 한국연소학회:학술대회논문집
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• 2013.06a
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• pp.97-98
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• 2013

Flame behaviors in meso-scale rectangular channels are largely influenced by heat recirculation through wall. In order to investigate the effects of wall thermal property on the heat recirculation and flame behaviors, meso-scale rectangular channels, of which upper and lower walls are made of quartz, stainless steel and silicon carbide and front and rear walls of quartz for flame visualization, were fabricated in this study. As a result, characteristic mixture velocities of propane-air flame, such as transition, stationary, and instability onset velocities, were measured for each channel and various mixture conditions. The results show that thermal conductivity has a close relationship to the characteristic velocities.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3282-3292
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• 1996

Flow velocity was measured using a hot wire anemometer. Turbulence intensity was in proportion to mean flow velocity regardless of swirl velocity. And integral length scale has proportional relation with swirl velocity regardless of measurement position. Flame speed calculated by radius of visualized flame was increased and then decreased according to lapse of time from spark. Maximum flame speed was increased according to increase of turbulence intensity. Burning speed and flame transport effect increased with increase of swirl velocity, but ratio of burning speed to flame speed decreased with increased of swirl velocity. Mass fraction burned versus volume fraction burned was increased in proportion to the increase of turbulence intensity, caused by increase of combustion promotion effect according to increase of turbulence intensity and scale.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.169-177
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• 1997

An experimental study has been conducted at an intermediate scale to study the effect of a cross flow on a purely buoyant fire. Video taping of the flame and post processing of the images by means of a novel technique provide a contour of a mean flame for all cases studied. This flame contour allows the determination of a mean flame length and a mean flame height. The mean flame length and height are recorded as functions of the forced flow velocity. Three dimensional flow patterns are formed in the flame trailing edge affecting both the mean flame length and height. The three dimensional patterns are studied systematically as functions of the cross flow velocity to quantify the effect of confinement on the flame geometry.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.849-854
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• 2005

The laminar flame concept in turbulent reacting flow is considered applicable to many practical combustion systems For turbulent premixed combustion under widely used flamelet concept, the flame surface is described as an infinitely thin propagating surface that such a Propagating front can be represented as a level contour of a continuous function G. In this study, for the Purpose of validating the LES of G-equation combustion model. LES of turbulent Premixed combustion with dynamic SGS model of G-equation in turbulent channel flow are carried out A constant density assumption is used. The Predicted flame propagating speed is goof agreement with the DNS result of G. Bruneaux et al.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.128-134
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• 2006

A characterization of turbulent reacting flows has proved difficult owing to the complex interaction between turbulence, mixing, and combustion chemistry. There are many types of time scales in turbulent flame which can determine flame structure. This counter jet type premixed burner produces high intensity turbulence. The goal is to gain better insights into the flame structures at high turbulence. 6 propane/air flames gave been studied with high velocity fluctuation in bundle type nozzle and in one hole type nozzle. By measuring velocity fluctuation, turbulent intensity and integral length scale are obtained. And sets of OH LIF images were processed to see flame structure of the mean flame curvatures and flame lengths for comparison with turbulence intensity and turbulent length scales. The results show that the decrease in nozzle size generates smaller flow eddy and mean curvatures of the flame fronts, and a decrease in Damkohler number estimated from flow time scale measurement.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.57-62
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• 2001

The effect of micro scale turbulence on flame structure and stability were experimentally investigated by changing the area of micro turbulence generator(MTG) and air velocity in terms of low NOx and high efficiency combustion. NOx and CO concentration were also measured for different MTG areas to investigate whether a vane swirler having MTG has a possibility of using as part for low NOx combustor. From the obtained results, it is shown that flame stability region increases and flame size becomes small as MTG area increases since MTG in itself makes small scale recirculation flow and swirler does large scale recirculation one. It is also shown that low NOx concentration(about 20${\sim}$30ppm@$O_2$ 11%) is achieved for all MTG areas without any increase in CO concentration regardless of air velocity range tested in this study when the equivalence ratio is 0.7. The results obtained in this study can give basic guideline for the design of compact low NOx high efficiency combustor using a vane swirler having MTG.

• 한국연소학회:학술대회논문집
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• 2012.11a
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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.