• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.311-313
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• 2014

High pressure combustion with multiphase--liquid, gas, and supercritical phase--mixtures are widely used technology in the high efficiency liquid propellent rocket engine. This is the typical characteristics differentiate from the combustor of conventional air-breathing engines. Therefore, successful research of high pressure combustion at supercritical condition is essential to develope a high efficiency liquid rocket engine. Numerical studies have been carried out to explore capabilities of numerical method for LOx-CH4 non-premixed flames at high pressure. In this paper, corresponding numerical results are presented and compared with experimental result of MASCOTTE facility.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.7-18
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• 2000

Numerical simulations of counterflow non-premixed $CH_4/C_2HCl_3/Air$ flames added 8%(by volume) C2HCl3 on the fuel side are conducted at atmospheric pressure using a detailed chemical reaction mechanism in order to understand the effect of strain rates. A detailed sensitivity analysis is also performed in order to assess the relative influence of each reaction on the flame established at a strain rate of 200s-1. The structure of flames (i.e., temperature, velocity, and concentration of species) established at both a strain rate of 150s-1 and 300s-1 are investigated. As the strain rate increases, the "flame zone" is restricted to a narrower range and the position of maximum temperature is shifted to the fuel side. The concentrations of major species, H2O, CO, H2, HCl, Cl2, and Cl are decreased with increased strain rate. The reaction involving chlorine, CH4 + Cl $\rightarrow$ CH3 + HCl, instead of the reaction, CH4 + H $\rightarrow$ CH3 + H2 influences the consumption of methane. C2HCl3 + OH $\rightarrow$ CHCl2 + CHOCl and HCl + OH $\rightarrow$ H2O + Cl, are major reactions, through which OH radicals are consumed.

• Journal of the Korean Society of Combustion
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• v.17 no.4
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• pp.30-37
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• 2012

The flame lengths and NOx emission characteristics of syngas $H_2$/CO turbulent non-premixed jet flames were investigated. The flame length which is the main parameter governs NOx emission was studied for various syngas compositions. The flame length was compared with previous correlation between Froude number and flame height and it shows that they have good agreements. It was confirmed that the turbulent jet flames herein investigated are in the region of buoyancy-momentum transition. NOx emission was reduced with increased Reynolds number and CO contents in syngas fuel and with decreased fuel nozzle diameter which is attributed by decreased flame residence time. Previous EINOx scaling based on flame residence time of $L_f^3/(d_f^2U_f)$ satisfies only the jet flame in momentum-dominated region, not buoyancy-momentum transition region. The simplified flame residence time ($L_f/U_f$) was adopted in modified EINOx scaling. The modified scaling satisfies the jet flames not only in momentum-dominated region but in buoyancy-momentum transition region. The scaling is also satisfied with $H_2$/CO syngas jet flames.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.183-184
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• 2014

The multi-environment probability density function model has been applied to simulate the turbulent stratified premixed flames. The direct quadrature method of moments (DQMOM) has been adopted to solve the transport PDF equation due to its computational efficiency and robustness. Computations are made for the non-swirling turbulent stratified premixed flames including SWB1, SWB5 and SWB9. The numerical results obtained in this study are precisely compared with experimental data in terms of axial velocity, unconditional means and conditional means for scalar field including temperature and species mass fraction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.730-736
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• 2005

It has been reported that the interacting multiple jet flames of propane fuel are not extinguished even at the choking velocity at the nozzle exit if eight small nozzles are arranged along the imaginary circle of $40{\sim}72$ times the diameter of single nozzle. In this research, experiments were conducted to know the NO and CO emission characteristics of the interacting flames. Measurements along the centerline of the flame revealed that decrease in CO concentration was followed by the NO decrease and $O_2$ increase. It was found that interacting flame emitted less NO than that of similar area single jet flame. Also, NO emission of partially premixed interacting flame was decreased up to $17\%$ of that of non-premixed multiple jet flame. Though the mechanism of the NO reduction was not clear from this experiment, it's been shown that partially premixed multiple jet flames could be used to achieve clean and highly stable combustion.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.237-240
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• 2006

Hybrid propulsion systems provide many advantages in terms of stable operation and safety. However, classical hybrid rocket motors have lower fuel regression rate and combustion efficiency compared to solid propellant rocket motor. Accordingly, the recent research efforts are focused on the improvement of engine efficiency and regressionrate in the hybrid rocket engine. The present study has numerically investigated the combustion processes and the flame structure in the hybrid rocket engine. The turbulent combustion is represented by the flamelet model and Low Reynolds number $k-{\varepsilon}$turbulent model is employed to reduce the uncertainties for convective heat transfer near solid fuel surface having strong blowing effect. Numerical results suggest that the present approach is capable of realistically simulating the combustion characteristics of the hybrid rocket engines.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1458-1464
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• 2002

$CO_2$ is well known greenhouse gas which is the major source of global warming. Reducing $CO_2$ emission in combustion process can be achieved by increasing combustion efficiency, oxygen enriched combustion and recirculation of the emitted $CO_2$ gas. Stability of non-premixed flame in oxygen enriched environment will be affected by the amount of oxygen, kind of diluents and fuel exit velocity. The effects of these parameters on flame liftoff and blowout are studied experimentally oxidizer coflowing burner. Experiments were divided into three cases according as where $CO_2$gas was supplied. - 1) to coflowing air, 2) to fuel with 0$_2$-$N_2$ coflow, 3) to coflowing oxygen. Flame in air coflowing case was lifted in turbulent region. Flame lift and blowout in laminar region with the increase in $CO_2$ volume fraction in $CO_2$-Air mixture makes flame lift and blowout in laminar region. Increase in oxygen volume fraction makes flame stable-i.e. flame liftoff and blowout occur at higher fuel flowrates. Liftoff height was non-linear function of nozzle exit velocity and affected by the $O_2$ volume fraction. It was found that the flame in $O_2$-$N_2$ coflow case was more stable than $O_2$-$CO_2$ case, Liftoff heights vs (nozzle exit velocity/laminar burning velocity)$^{3.8}$ has a good correlation in $O_2$-$CO_2$ oxidizer case.

• Journal of the Korean Society of Visualization
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• v.9 no.4
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• pp.35-40
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• 2011

An experimental investigation of the characteristic of non-premixed lifted flames with nozzle hole-tone of high-frequency has been performed. Before the fuel was supplied to nozzle, the fuel was supplied through a burner cavity which was located under the nozzle. The fuel passed through the excitation cavity under the influence of the high-frequency affects the lifted flame characteristics. The measurements were performed in flow range that occurs lifted flame and blow out. When the high-frequency is generated from burner cavity, the lifted length became shorter, and noise reduced comparing to unexcitation case. Additionally, operating flow range was increased and diameter of flame base became smaller with high-frequency effect. Through this experiments, it's ascertained that the high-frequency excitation can be adopted with effective method for flame stability and noise reduction.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.211-213
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• 2014

Simultaneous measurements of planar laser-induced fluorescence (PLIF) of OH radicals and particle image velocimetry (PIV) were used to investigate the strain rates and OH structure characteristics of turbulent syngas non-premixed jet flames close to blowoff. Mean values of the maximum principal strain rate on OH layer decreases with the axial distance, and its standard deviation is significantly large upstream. Strain rate on stabilization region of the stable flame is only about a half of that of the flame near blowoff.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.326-331
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• 2003

Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improvement of the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. Especially lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Flame stability became improved since lift-off and blowout limit increased much with increase of OEC.