• Journal of the Korean Society of Combustion
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• v.8 no.4
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• pp.15-23
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• 2003

The zone conditional two-fluid equations are derived and validated against DNS database of a premixed turbulent flame. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin f1amelets. The transverse component may be larger than the axial component for a distributed pdf of the flamelet orientation angle, while the opposite occurs due to redistribution of turbulent kinetic energy and flamelet orientation normal to the flow at the end of a flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface. Ad hoc modeling of some interfacial terms may be required for further application of the two-fluid model in turbulent combustion simulations.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.1009-1018
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• 2002

The Representative Interactive Flamelet (RIF) concept has been applied to numerically simulate the combustion processes and pollutant formation in the direct injection diesel engine. Due to the ability for interactively describing the transient behaviors of local flame structures with CFD solver, the RIF concept has the capabilities to predict the auto-ignition and subsequent flame propagation in the diesel engine combustion chamber as well as to effectively account for the detailed mechanisms of soot formation, NOx formation including thermal NO path, prompt and nitrous 70x formation, and reburning process. Special emphasis is given to the turbulent combustion model which properly accounts for vaporization effects on the mixture fraction fluctuations and the pdf model. The results of numerical modeling using the RIF concept are compared with experimental data and with numerical results of the commonly applied procedure which the low-temperature and high-temperature oxidation processes are represented by the Shell ignition model and the eddy dissipation model, respectively. Numerical results indicate that the RIF approach including the vaporization effect on turbulent spray combustion process successfully predicts the ignition delay time and location as well as the pollutant formation.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.24-32
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• 2002

The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically analyzed. The unsteady flamelet modeling based on the RIF (Representative Interactive Flamelet) concept has been employed to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants(NOx, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of EPFM(Eulerian Particle Flamelet Model) approach. Computations are made for the various initial conditions of pressure, temperature, and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high pressure and temperature environment.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.41-45
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• 2002

The zone-conditioned CMC equations are derived by taking an unconditional average of the generic conservation equations multiplied by delta and Heaviside functions in terms of mixture fraction and reaction progress variable. The resulting equations are essentially in the same form as the single zone CMC equations except for separate flow fields for burned and unburned gas. The zone-conditioned two-fluid equations are applied to a stagnating turbulent premixed flame brush of Cheng and Shepherd[5l. It is shown that the flame stretch factor is of crucial importance to accurately reproduce the measured mean reaction progress variable and conditional velocities. Further work is in progress for the relationship between surface and volume averages and extension to partially premixed combustion on the basis of a triple flame structure, e. g. in a lifted turbulent diffusion flame.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.88-97
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• 2001

The present study numerically investigates the fuel-air mixing characteristics, flame structure, and pollutant emission inside a double-swirler combustor. A PSR(Perfectly Stirred Reactor) based microstructural model is employed to account for the effects of finite rate chemistry on the flame structure and NO formation. The turbulent combustion model is extended to nonadiabatic flame condition with radiation by introducing an enthalpy variable, and the radiative heat loss is calculated by a local, geometry-independent model. The effects of turbulent fluctuation are taken into account by the joint assumed PDFs. Numerical model is based on the non-orthogonal body-fitted coordinate system and the pressure/velocity coupling is handled by PISO algorithm in context with the finite volume formulation. The present PSR-based turbulent combustion model has been applied to analyze the highly intense turbulent nonpremixed flame field in the double swirler combustor. The detailed discussions were made for the flow structure, combustion effects on flow structure, flame structure, and emission characteristics in the highly intense turbulent swirling flame of the double swirler burner.

• 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.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.89-95
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• 2006

This study has numerically modelled the combustion processes of the turbulent swirling premixed lifted flames in the low-swirl burner (LSB). In these turbulent swirling premixed flames, the four tangentially-injected air jets induce the turbulent swirling flow which plays the crucial role to stabilize the turbulent lifted flame. In the present approach, the turbulence-chemistry interaction is represented by the level-set based flamelet model. Two-dimensional and three-dimensional computations are made for the various swirl numbers and nozzle length. In terms of the centerline velocity profiles and flame liftoff heights, numerical results are compared with experimental data The three-dimensional approach yields the much better conformity with agreements with measurements without any analytic assumptions on the inlet swirl profiles, compared to the two-dimensional approach. Numerical clearly results indicate that the present level-set based flamelet approach has realistically simulated the structure and stabilization mechanism of the turbulent swirling stoichiometric and lean-premixed lifted flames in the low-swirl burner.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.81-89
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• 2002

The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically analyzed. The unsteady flamelet modeling based on the RIF (representative interactive flamelet) concept has been employed to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants(NOx, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of EPFM(Eulerian particle flamelet model) approach. Computations are made for the various initial conditions of pressure, temperature, and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high pressure and temperature environment.

• International Journal of Automotive Technology
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• v.6 no.6
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• pp.571-577
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• 2005

Combustion of turbulent sprays in a direct injection diesel engine is modeled by the conditional moment closure (CMC) model. The CMC routines are combined with the KIVA code to provide conditional flame structures to determine mean state variables, instead of mean reaction rates. An independent transport equation is solved for each flame group with equal mass of sequentially evaporating fuel vapor. CMC calculation begins as the fuel mass for each flame group begins to evaporate with corresponding initialization conditions. Comparison is made with measured pressure traces for four operating conditions at different rpm's and injection conditions. Results show that the CMC model with multiple flame histories can successfully be applied to ignition and mixing-controlled combustion phases of a diesel engine.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.330-333
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• 2008

Present paper introduces the research activities on fuel-air mixing and combustion of supersonic turbulent flows in scramjet combustor carried out in Aerospace Combustion and Propulsion Laboratory of the department of Aerospace Engineering of the Pusan national University. Also, an introduction will be given to the characteristics of the supercritical hydrocarbon fuel combustion in a practical scramjet engine and its numerical modeling approaches.