• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.233-234
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• 2014

Lean-rich combustion system was composed both fuel-lean and fuel-rich flame at once. Each of fuel-lean and fuel-rich combustion types to reduce Thermal $NO_x$ and obtain flame stability. This study was confirmed a stability of flame through variation of flame shape that EGR was applied and compared the emission characteristics of EGR lean-rich combustion system to normal premixed combustion system at real condition to review a utility of the system. As a result, emission index of $NO_x$ and CO generated from EGR lean-rich combustion system at global equivalence ratio is 0.85 just half level($NO_x$ 0.31 g/kg, CO 0.08g/kg) compared to the amount generated from normal premixed combustion system at equivalence ratio is 0.78.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.819-827
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• 1987

The purpose of the present investigation is to examine the effect of water addition on combustion efficieny. In this research, fuel and additive water are injected into a burner in the form of vapors through separate needle valves, the flame temperature and concentrations of soot, CO and unburned hydrocarbons were measured in a premixed flame. The results are obtained to be: In the fuel lean region, the reduction rate of CO, soot and HC by water injection increases slightly, but there is no change in the combustion efficiency. On the other hand, in the fuel rich region, the reduction rate of CO, Soot and HC by water injection increases more than that of the fuel lean region. Accordingly, combustion efficiency increases.

• Journal of the Korean Society of Combustion
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• v.18 no.4
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• pp.44-52
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• 2013

Important role of chemical interaction in flame extinction was numerically investigated in downstream interaction among lean(rich) and lean(rich) premixed as well as partially premixed $H_2$-air and CO-air flames. The strain rate varied from 30 to $5917s^{-1}$ until interacting flame could not be sustained anymore. Flame stability diagrams mapping lower and upper limit fuel concentrations for flame extinction as a function of strain rate are presented. Highly stretched interacting flames were survived only within two islands in the flame stability map where partially premixed mixture consisted of rich $H_2$-air flame, extremely lean CO-air flame, and a diffusion flame. Further increase in strain rate finally converges to two points. Appreciable amount of hydrogen in the side of lean $H_2$-air flame also oxidized the CO penetrated from CO-air flame, and this reduced flame speed of the $H_2$-air flame, leading to flame extinction. At extremely high strain rates, interacting flames were survived only by a partially premixed flame such that it consisted of a very rich $H_2$-air flame, an extremely lean CO-air flame, and a diffusion flame. In such a situation, both the weaker $H_2$-air and CO-air flames were parasite on the stronger diffusion flame such that it could lead to flame extinction in the situation of weakening the stronger diffusion flame. Particular concerns are focused on important role of chemical interaction in flame extinction was also discussed in detail.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.9-14
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• 2010

Numerical simulations of freely propagating fuel-rich $CH_4/CH_3Cl$ premixed flames were performed at atmospheric pressure in order to understand the effect of the oxygen enrichment on the production of PAH. A chemical kinetic mechanism was used, which involved 157 gas-phase species and 1693 forward reactions. The calculated flame speeds were compared with the experiments for the flames established on the equivalence ratios of 1~1.6, the results of which were in good agreement. As the level of oxygen enrichment was increased, the concentrations of one or four ring aromatic hydrocarbons were decreased. This might cause the fact that the contribution of PAH species to soot was weakened.

• Journal of the Korean Society of Combustion
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• v.15 no.3
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• pp.1-7
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• 2010

Edge flames have been interested as a basic structure that is concerned to flame stabilization and re-ignition of non-premixed flames. The edge flame consists of a lean premixed flame, a rich premixed flame, and a diffusion flame. In order to investigate fundamental structures of the edge flames at the conditions near the flammability limits, edge flames were stabilized within a heated narrow channel. Highly diluted partially premixed methane was used, and the flow rates of air and the partially premixed mixture were controlled. Various flame behaviors, including a transition between ordinary edge flames and premixed flames, were observed. Flame stabilization characteristics were examined as well. All flame stabilization conditions in this study showed a similar trend: characteristic time scales were inversely proportional to the equivalence ratio defined at the burner inlet. Finally, an interesting flame structure having a weak diffusion branch enveloped by a closed premixed branch was found near the flammability limits even in a fuel-air mixing layer. This structure was named as a "flame-drop" and the importance of this structure was first suggested.

• Journal of the Korean Society of Combustion
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• v.20 no.2
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• pp.28-35
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• 2015

In this study, the CH4/air lean-rich combustion system with exhaust gas recirculation (EGR) was investigated to explore the potential for lowering pollutant emissions. To achieve this purpose, experiments of lean-rich combustion system with EGR were conducted to measure the changes in the characteristics of the pollutant emission and flame shape with various equivalence ratios and EGR rates. Here, this study was applied to the fuel distribution ratio of 3:1 for the formation of the lean and rich flames. Additionally, the results were compared with $CH_4$/air lean premixed combustion system. The results show that flame shape of lean-rich combustion system was determined by lean and rich equivalence ratios (${\Phi}_L$ and ${\Phi}_R$) and stratified flame was formed with increasing ${\Phi}_R$. According to the pollutant emission characteristics based on experimental results, the NOx and CO emission index (EINOx and EICO) decreased with increasing EGR rate. Especially, in the range needed to form a stable flame, the reduction rates of EINOx and EICO were approximately 47% and 48% for an EGR rate of 25%, global equivalence ratio of 0.85 and ${\Phi}_L$ of 0.80 compared with lean premixed combustion system (${\Phi}$ = 0.78).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.1
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• pp.7-14
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• 2008

It has been reported that partially premixed interacting flame could be sustained till sonic exit velocities if eight small nozzles are arranged optimally and one nozzle on the center is fed small amount of fuel. But the equivalence ratios in this experiments were 20-60. In this research, experiments were conducted to know the effects of lean-rich staging in multiple jet flames on the blowout velocity. The fuel mole tractions in the fuel-air mixture, the nozzle exit velocity and the diameter between adjacent nozzles were alternatively changed. When the lower mole fraction fuel was fed to the nozzles located near the center and small amount of fuel to the center nozzle, flame was not extinguished even at the nozzle exit velocity of 200m/s. Also the interacting flame could be sustained till that velocity when four small size nozzles for lean mixture were located within the arrangement of four nozzles for rich mixture and configured optimally.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.1
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• pp.88-95
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• 1999

This study investigates the effects of different kind fuels on the flame structure by using the numerical simulation in triple flame made by a co-flowing fuels-air stream based on the elementary chemical reaction mechanism. Methane and Hydrogen were used as fuel for this study. In order to interpret the result of the study on numerical simulation Skeletal chemistry is employe as the elementary chemical reaction mechanism for methane Gutheil's as an offset ele-mentary chemical reaction mechanism for hydrogen. The result of this study is as follows. In com-parison between the apparent burning velocity change of triple flame and the one-dimensional pre-mixed flame hydrogen fuel flame is higher than methane fuel flame. The flame thrusts out for-ward in the down stream of the boundary between air-fuel mixture and air stream and a part of the flow is bent and forks out in this protruding flame so that a triple flame is originated.

• Journal of the Korean Society of Combustion
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• v.17 no.3
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• pp.17-29
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• 2012

The effects of strain rate and preferential diffusion of $H_2$ on flame extinction are numerically studied in interacting premixed syngas-air flames with fuel compositions of 50% $H_2$ + 50% CO and 30% $H_2$ + 70% CO. Flame stability diagrams mapping lower and upper limit fuel concentrations at flame extinction as a function of strain rate are examined. Increasing strain rate reduces the boundaries of both flammable lean and rich fuel concentrations and produces a flammable island and subsequently even a point, implying that there exists a limit strain rate over which interacting flame cannot be sustained anymore. Even if effective Lewis numbers are slightly larger than unity on extinction boundaries, the shape of the lean extinction boundary is slanted even at low strain rate, i.e. $a_g=30s^{-1}$ and is more slanted in further increase of strain rate, implying that flame interaction on lean extinction boundary is strong and thus hydrogen (as a deficient reactant) Lewis number much less than unity plays an important role of flame interaction. It is also shown that effects of preferential diffusion of $H_2$ cause flame interaction to be stronger on lean extinction boundaries and weaker on rich extinction boundaries. Detailed analyses are made through the comparison between flame structures with and without the restriction of the diffusivities of $H_2$ and H in symmetric and asymmetric fuel compositions. The reduction of flammable fuel compositions in increase of strain rate suggests that the mechanism of flame extinction is significant conductive heat loss from the stronger flame to ambience.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.4
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• pp.44-51
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• 2017

An experimental results on the dynamic characteristics of hydrocarbon/air premixed flames with ultrasonic standing waves are presented and compared. Images of the propagating flames were acquired by using a high-speed camera, and the flame behavior of methane/air and propane/air premixed flame were closely scrutinized through the image post-processing. At the fuel-lean conditions, the flame propagation velocity increased due to the intervention of the ultrasonic standing wave and vice versa at the fuel-rich conditions.