• Journal of ILASS-Korea
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• v.18 no.4
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• pp.202-208
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• 2013

The present study aims to investigate the flow characteristics with respect to fuel type and equivalence ratio in the flame spray coating process. The flame spray flow is characterized by much complex phenomena including combustion, turbulent flows, and combined heat transfer. The present study numerically simulated the flam spray process and examined the gas dynamics involving combustion, gas temperature and velocity distributions in flame spray process by using commercial computational fluid dynamics (CFD) code of FLUENT (ver. 13.0). In particular, we studied the effect of fuel type and equivalence ratio on thermal and flow characteristics which could substantially affect the coating performance. From the results, it was found that the gas temperature distributions were varied with different fuels because of reaction times were different according to the fuel type. The equivalence ratio also could change the spatial flame distribution and the characteristics of coated layer on the substrate.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.65-70
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• 2001

OH radical and NOx have been measured in a methane-air partially premixed flame using PLIF technique to define preheated air combustion characteristics. The temperature of mixture is determined by 300K, 400K, 600K and 800K below the auto-ignition temperature respectively. Flame height increases as equivalence ratio increased. As initial enthalpy is supplied, the radius of flame was increased and much amount of yellow flame in rich equivalence ratio was observed. This is due to the faster burning velocity. Also initial oxidization begins earlier as the initial temperature of mixture increased. It means that height of premixed flame front decreased. This phenomenon can be observed OH PLIF image. The qualitative analysis of OH concentration in the PLIF image shows that overall OH concentration increases with equivalence ratio and the initial temperature of mixture increased. At the preheating temperature goes up, axial gradient of OH concentration is less steep than that of lower temperature condition. This may identify that combustion reacts continuously, so preheated air combustion can evade the local heating and make high temperature indiscriminately in the overall reaction zone.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1652-1661
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• 2000

A visualization study using the schlieren method is adopted in an optically-accessible, cylindrical constant volume combustion chamber to identify the mechanism of ignition energy and ignition system interaction in spark ignited, lean gasoline-air mixture. In order to research the effects of ignition system on flame propagation, two kinds of ignition system are designed, and several kinds of spark plugs are tested and evaluated. To control the discharge energy, the dwell time is varied. The initial flame development is quantified in terms of 2-D images which provides information about the projected flame area and development velocity as a function of ignition system and discharge energy. The results show that high ignition energy and extended spark plug gap can shorten the combustion duration in lean mixtures. The material, diameter and configuration of electrodes the flame development by changing the transfer efficiency from electrical energy to chemical energy and discharge energy. However these factors do not affect of flame development as much a ignition energy or extended gap does.

• Journal of ILASS-Korea
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• v.21 no.1
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• pp.37-46
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• 2016

For the SI engines, at only full load, the pumping loss has a negligible effect, while at part load conditions, the pumping loss increases. To avoid the pumping loss, the spark-ignited engines are designed to inject gasoline directly into the combustion chamber. In the spark-ignited direct-injection engines, ignition probability is important for successful combustion and the flame propagation characteristics are also different from that of pre-mixed combustion. In this paper, a visualization experiment system is designed to study the ignition probability and combustion flame characteristics of spark-ignited direct-injection CNG fuel. The visualization system is composed of a combustion chamber, fuel supply system, air supply system, electronic control system and data acquisition system. It is found that ambient pressure, ambient temperature and ambient air flow velocity are important parameters which affect the ignition probability of CNG-air mixture and flame propagation characteristics and the injected CNG fuel can be ignited directly by a spark-plug under proper ambient conditions. For all cases of successful ignition, the flame propagation images were digitally recorded with an intensified CCD camera and the flame propagation characteristics were analyzed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.11
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• pp.1407-1416
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• 2004

A two-dimensional direct numerical simulation was performed to investigate the flame structure of CH$_4$/$N_2$-Air counterflow nonpremixed flame interacting with a single vortex. The detailed transport properties and a modified 16-step augmented reduced mechanism based on Miller and Bowman's detailed chemistry were adopted in this computation. The results showed that an initially flat stagnation plane, on which an axial velocity was zero, was deformed into a complex-shaped plane, and an initial stagnation point was moved far away from a vortex head when the counterflow field was perturbed by the vortex. It was noted that the movement of stagnation point could alter the species transport mechanism to the flame surface. It was also identified that the altered species transport mechanism affected the distributions of the mixture fraction and the scalar dissipation rate.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 1999.04a
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• pp.243-244
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• 1999

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.213-223
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• 1997

Premixed flame is better than diffusion flame to accomplish a high loading combustion. Since the turbulent characteristics of unburned mixture has a great influence on the flame structure, it is general that many researchers realize a high loading combustion with strengthening turbulent intensity of unburned mixture. Because turbulent premixed flame reacts efficiently on the condition of distributed reaction region, we made high turbulent premixed flame in the doubled impingement field. We investigated turbulent characteristics of unburned mixture with increasing shear force and visualized flames with direct and Schlieren photographs. And the combustion characteristics of flame was elucidated by instantaneous temperature measurement with a thermocouple, by ion currents with a micro electrostatic probe, by radical luminescence intensity and local equivalence ratio. Extremely strong turbulent of small scale is generated by impingement of mixture, and turbulent intensity of unburned mixture increased with the mean velocity. As a result of direct photographs, visible region of flame became longer due to increasing central direction flux. But as strengthed turbulent intensity, visible region of flame turned to shorter and reaction occurred efficiently. As strengthened turbulent intensity of mixture with increasing flux of central direction, maximum fluctuating temperature region moved to radial direction and fluctuation of temperature became lower. The reason is influx of central direction which caused flame zone to move toward radial direction, to maintain flame zone stable and to make flame scale smaller.

• Journal of the Korean Society of Combustion
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• v.11 no.3
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• pp.36-43
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• 2006

The modulated LII technique has been suggested for the measurement of axial velocity profiles of laminar diffusion flames. The theoretical background is explained based on the blackbody radiation and LII signal. Experimentally, soot particles in ethylene diffusion flames are heated by a modulated Ar-ion laser beam. LII signals and their phase angles are measured using a lock-in amplifier at the different flame heights and the axial flow velocities are obtained from the measured phase angle delay informations. The measured velocities are similar to those from LDV measurements under the same operating conditions. The effects of laser power, LII signal wavelength, and modulation frequencies are not sensitive to the velocity measurement. However, the choice of an optical chopper blade type could affect the measurement result. The use of a 6/5 chopper blade showed the better result that is. possibly due to the square shape of modulated laser beam. This study successfully demonstrated that axial flow velocities of laminar diffusion flames can be measured by a new technique utilizing LII signal, which does not need particle seeding unlikely to LDV or PIV techniques.

• 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.

• Fire Science and Engineering
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• v.27 no.6
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• pp.64-69
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• 2013

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to simulate an engine nacelle fire and to complement the previous experimental results of the bluff body stabilized flames. Fire Dynamic Simulator (FDS) based on the Direct Numerical Simulation (DNS) was employed to clarify the characteristics of reacting flow around bluff body. The overall reaction was considered and the constant for reaction was determined from flame extinction limits of experimental results. The air used atmosphere and the fuel used methane. For both fuel ejection configurations against an oxidizer stream, the flame stability and flame mode were affected mainly by vortex structure near bluff body. In the coflow configuration, air velocity at the flame extinction limit are increased with fuel velocity, which is comparable to the experiment results. Comparing with the isothermal flow field, the reacting flow produces a weak and small recirculation zone, which is result in the reductions of density and momentum due to temperature increase by reaction in the wake zone.