• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3300-3305
• /
• 2007

Ignition delay of second injection of HSDI diesel engine was usually much shorter than that of first injection. It is due to the interaction between radicals generated during the combustion process, and mixed gas of second injection. In this paper, To analyze combustion phenomena of multiple injection mode in HSDI diesel engine effectively, two-dimensional flamelet combustion model was modified. To reduce calculation time, two-dimensional flamelet equations were only applied near stoichiometric region. If this region was ignited, species and temperature of other region were changed to the steady-state solutions of one dimensional flamelet equations. By this method calculation time for solving flamelet equations was reduced to 20 percents, thought the results were almost same. Modified flamelet combustion model was coupled to commercial CFD code interactively using user subroutine.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
• /
• pp.9-16
• /
• 2000

The flamelet concept has been widely applied to numerically simulate complex phenomena occurred in nonpremixed turbulent flames last two decades, and recently broadened successfully the applicable capabilities to various combustion problems from simple laboratory flames to gas turbine engine, diesel spray combustion and partially premixed flames. The paper is focused on brief review of recently noticeable work related to flamelet modeling, which includes Lagrangian flamelet approach, RIF concept as well as steady flamelet approach. The limitation of steady flamelet assumption, the effect of transient behavior of flamelets, and the effect of spray vaporization on PDF model have been discussed.

• 한국연소학회지
• /
• 제4권2호
• /
• pp.51-62
• /
• 1999

NOx formation in turbulent flames is strongly coupled with temperature, superequilibrium concentration of O radical, and residence time. This implies that in order to accurately predict NO level, it is necessary to develop sophisticated models able to account for the complex turbulent combustion processes including turbulence/chemistry interaction and radiative heat transfer. The present study numerically investigates the turbulent nonpremixed hydrogen jet flames using the laminar flamelet model. Flamelet library is constructed by solving the modified Peters equations and the turbulent combustion model is extended to nonadiabatic flame by introducing the enthalpy defect. The effects of turbulent fluctuation are taken into account by the presumed joint PDFs for mixture fraction, scalar dissipation rate, and enthalpy defect. The predictive capability of the present model has been validated against the detailed experimental data. Effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.

• 한국연소학회지
• /
• 제5권2호
• /
• pp.1-8
• /
• 2000

The flamelet concept has been widely applied to numerically simulate complex phenomena occurred in nonpremixed turbulent flames last two decades, and recently broadened successfully the applicable capabilities to various combustion problems from simple laboratory flames to gas turbine engine, diesel spray combustion and partially premixed flames. The paper is focused on brief review of recently noticeable work related to flamelet modeling, which includes Lagrangian flamelet approach, RIF concept as well as steady flamelet approach. The limitation of steady flamelet assumption, the effect of transient behavior of flamelets, and the effect of spray vaporization on PDF model have been discussed.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
• /
• pp.93-104
• /
• 1999

NOx formation in turbulent flames is strongly coupled with temperature, superequilibrium concentration of O radical, and residence time. This implies that in order to accurately predict NO level, it is necessary to develop sophisticated models able to account for the complex turbulent combustion processes including turbulence/chemistry interaction and radiative heat transfer. The present study numerically investigates the turbulent nonpremixed hydrogen jet flames using the laminar flamelet model. Flamelet library is constructed by solving the modified Peters equations and the turbulent combustion model is extended to nonadiabatic flame by introducing the enthalpy defect. The effects of turbulent fluctuation are taken into account by the presumed joint PDFs for mixture fraction, scalar dissipation rate, and enthalpy defect. The predictive capability of the present model has been validated against the detailed experimental data. Effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.

• Nuclear Engineering and Technology
• /
• 제54권4호
• /
• pp.1321-1335
• /
• 2022

This study was conducted to investigate the effect of absorption coefficient models on the P1 radiation model for a premixed hydrogen flame containing the water vapor. A CFD combustion simulation analysis was performed using XiFoam, one of the open-source CFD solvers in OpenFOAM. The solver using the flamelet combustion model has been modified to implement radiative heat transfer. The absorption coefficient models used in this study the grey-mean model and constant model, and for comparison, case without radiation was added. This CFD simulation study consisted of benchmarking the THAI HD-15 and HD-22 experiments. The difference between the two tests is the inclusion of water vapor in the condition before ignition. In the case of the HD-22 experiment containing water vapor in the initial condition, the simulation results show that the grey-mean absorption coefficient model has a strong influence on the temperature decrease of the flame and on the change in pressure inside the vessel.

• 한국연소학회지
• /
• 제1권2호
• /
• pp.51-58
• /
• 1996

The coherent flamelet model(CFM) is applied to symmetric counterflow turbulent premixed flames. The flame source term is set proportional to the turbulence intensity to reproduce the experimental correlation of Abdel-Gayed et al. for the turbulent burning velocity. Flame quenching by the turbulent rate of strain is modeled by an additional multiplication factor to the flame source term. A modified form of CFM is employed to consider coexistence of burned and unburned premixture with ambient air. The predicted flame position and turbulent flow field coincide well with the experimental data of Kostiuk et al., although there is some discrepancy in the radial rms velocity component and integral length scale near the symmetric plane.

• 한국자동차공학회논문집
• /
• 제13권1호
• /
• pp.60-67
• /
• 2005

Mild combustion or Flameless oxidation(FLOX) have been considered as one of the most prospective clean-combustion technologies to meet both the targets of high process efficiency and low pollutant emissions. A mild combustor with high air preheating and strong internal exhaust gas recirculation is characterized by relatively low flame temperature, low NOx emissions, no visible flame and no sound. In this study, the Steady Flamelet Approach has been applied to numerically analyze the combustion processes and NOx formation in the mild combustor. The detailed discussion has been made f3r the basic characteristics of mild combustor, numerical results and limitation of the present combustion modeling.

• International Journal of Automotive Technology
• /
• 제7권2호
• /
• pp.129-137
• /
• 2006

The representative interactive flamelet(RIF) concept has been applied to numerically simulate the combustion processes and pollutant formation in the HSDI diesel engine. In order to account for the spatial inhomogeneity of the scalar dissipation rate, the eulerian particle flamelet model using the multiple flamelets has been employed. The vaporization effects on turbulence-chemistry interaction are included in the present RIF procedure. the results of numerical modeling using the rif concept are compared with experimental data and with numerical results of the widely-used ad-hoc combustion model. Numerical results indicate that the rif approach including the vaporization effect on turbulent spray combustion process successfully predicts the ignition delay characteristics as well as the pollutant formation in the HSDI diesel engines.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2006년도 제27회 추계학술대회논문집
• /
• pp.237-240
• /
• 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.