• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.91-101
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• 2004

With the mathematic linear model of a combustor which consists of a combustion chamber and injectors, the analysis of low frequency dynamic characteristics of a liquld-propellant rocket engine combustor was performed. Propellant mass flowrate was varied by combustion chamber pressure feedback, therefore low frequency oscillation was appeared. Increasing the time constant of a combustion chamber and injector pressure differences and decreasing combustion time delay increased the combustor system stability. The variation of injector time constant little affected stability. The system was always stable, when there was no combustion time delay. Increasing combustion time delay decreased oscillation frequency and damping ratio, and the system eventually became unstable.

• Journal of the Korean Society of Combustion
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• v.22 no.1
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• pp.39-45
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• 2017

Combustion instability analysis of partially premixed model gas turbine combustor was conducted with 1D lumped method. Flame Transfer Function(FTF) was obtained with variation of fuel composition by Photo Multiplier Tube(PMT) and Hot Wire Anemometry(HWA). Decreasing instability frequency was observed when combustor length increased and multi-mode instability was confirmed. Instability frequency mode was changed while $H_2$ composition rate was increased and had agreement with experimental value. This work confirms that prediction of longitudinal combustion instability mode of partially premixed combustor is possible using 1D lumped method.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.2
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• pp.24-33
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• 2021

Numerical study is conducted to analyze combustion instability in the partially premixed combustor. The simulations are performed according to fuel conditions, and Large Eddy Simulation(LES) model and PaSR combustion model are implemented in the solver. Comparison with the experimental result is conducted to confirm the validity of simulation, and quantitative and qualitative agreement is confirmed. The flame characteristics in the combustor are subsequently investigated, and the association with the occurrence of combustion instability is clarified. According to the simulation results, the flame length varies greatly depending on the fuel conditions. When the flame length becomes sufficiently long, flame-vortex interactions occurred around the wall sections, which works as the main cause of combustion instability.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.72-80
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• 2018

Combustion instabilities are caused by the feedback relationship between heat release perturbations and acoustic pressure oscillations in the combustor. Studies on the combustion instability in an annular combustor have recently received great attention due to the enhanced NOx requirement in aero-engines. In this study, a thermoacoustic network model was developed in order to calculate the acoustic characteristics for various modes in the annular combustor. The network model is combined with flame transfer function(FTF) in order to calculate the stability of the combustor. Numerical results are compared with measurement data.

• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1470-1478
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• 2004

In this paper, a new 'presumed' Probability Density Function (PDF) approach coupled with a Lagrangian tracking method is proposed for turbulent combustion modeling. The test and the investigation of the model are conducted by comparing the model results with DNS data for a premixed flame subjected in a decaying turbulent field. The newly constructed PDF, which incorporates the instantaneous chemical reaction term, demonstrates consistent improvement over conventional assumed PDF models. It has been found that the time evolution of the mean scalar, the variance and the mean reaction rate are strongly influenced by a parameter deduced by a Lagrangian equation which takes into account explicitly the local reaction rate. Tests have been performed for a moderate Damkohler number, and it is expected the model may cover a broader range of Damkohler number. The comparison with the DNS data demonstrates that the proposed model may be promising and affordable for implementation in a moment-equation solver.

• Journal of Power System Engineering
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• v.2 no.2
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• pp.20-26
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• 1998

Heat release data were obtained by analysis of cylinder diagrams from a test engine, naturally-aspirated small-size four-stroke DI diesel engine. These data were used to decide empirical coefficients of Whitehouse-Way's model, single zone combustion model. Finally, the comparison of calculated with experimental results was performed, and the accuracy of calculated versus experimental data of the model in predicting engine heat release and cylinder pressure was demonstrated.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.143-149
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• 2008

The present study is mainly motivated to investigate the vaporization, auto-ignition and spray combustion processes in DI diesel engine using DME and n-heptane. In order to realistically simulate the dimethyl ether (DME) spray dynamics and vaporization characteristics in high-pressure and high-temperature environment, the high-pressure vaporization model has been utilized. The interaction between chemistry and turbulence is treated by employing the Representative Interaction Flamelet (RIF) model. The detailed chemistry of 336 elementary steps and 78 chemical species is used for the DME/air reaction. Based on numerical results, the detailed discussion has been made for the distinctly different combustion characteristics of DME diesel engine in term of vaporization, ignition delay, pollutant formation, and heat release rate.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.192-198
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• 2004

A numerical study was conducted to determine the effects of high temperature air, including equivalent ratio on flow field, temperature, evaporation, and overall temperature distribution in gas turbine combustor. A sector model of a typical wall jet can combustor, featuring introduction of primary air and dilution air via wall jet, was used in calculations. Flow field and temperature distribution were analyzed. Operating conditions such as inlet temperature and overall equivalent ratio were varied from 373 to 1300 K, and from 0.3 to 0.6, respectively, while any other operating conditions were fixed. The RNG ${\kappa}-{\varepsilon}$ model and eddy breakup model were used for turbulence and combustion model respectively. It was found that the increase with the inlet air temperature, velocity in the combustor is accelerated and evaporation of liquid fuel is not affected in primary zone, high temperature inlet air enhances the evaporation and improves overall temperature distribution factor.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.67-70
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• 2012

Many computational fluid dynamic (CFD) simulations have treated the coal kinetics poorly due to large physical domain sizes and high computational complexity, particularly for the recent oxy-coal boilers. Furthermore, some modelers' lack of understanding of the kinetic rate model seems to worsen the simulation accuracy. This study is to suggest the importance of proper use of single-film global kinetic model generally used in CFD code to describe the oxy-fuel combustion of coal char through simple char burnout calculation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.659-669
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• 1997

The effects of exhaust gas recirculation on diesel engine combustion and soot/NOx emissions are numerically studied. The primary and secondary atomization is modelled using the wave instability breakup model. Autoignition of a diesel spray is modelled using the Shell ignition model. Soot formation is kinetically controlled and soot oxidation is represented by a model which account for surface chemistry. The NOx formation is based on the extended Zeldovich NOx model. Effects of injection timing and concentration of $O_{2}$ and CO$_{2}$ on the pollutant formation and the combustion process are discussed in detail.