• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1552-1565
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• 1992

Three dimensional numerical calculations were carried out for two different combustion chambers with the offset valve in order to investigate the swirl and the squish effects on the flow fields. The modified K-.epsilon. turbulence model considering the change of the density under the condition of the rapid compression and expansion of the pistion was used. During the compression process, it was found that the squish flow which controls the subsequent combustion process was produced due to the piston bowl in the bowl piston type combustion chambers but not for the flat piston type. The swirl velocity close to the solid body rotation was maintained in the flat piston type combustion chambers, but for the bowl piston type a resulting from the change of the solid body rotation was generated in the radial-circumferential plane. For the swirl ratio effect, as the swirl ratio increases, it was found that a large and strong vortex was generated in the radial-circumferential plane of bowl piston type combustion chambers because of the strong inward flows from the combustion chamber wall. These computational results were compared with the results of LDA measurement.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.37-42
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• 2001

This paper computes the bluff-body stabilized jet and flame. This study numerically investigates the nonpremixed $C_{2}H_{4}-air$ jet for the nonreacting case and the nonpremixed $CH_{3}OH-air$ turbulent flames for the reacting case using the laminar flamelet model on modified KIVA2 code. And this study predicts $NO_{x}$ formation characteristics using Eulerian Particle Flamelet Model. In the present study, the turbulent combustion model is applied to analyze both nonreacting and reacting case. And both standard $k-{\varepsilon}$ model and modified $k-{\varepsilon}$ model are used in nonreacting case. Calculations are compared with experimental data in terms of velocity, mixture fraction, mixture fraction Root Mean Square and Temperature. The present model correctly predicts the essential features of flame structures and $NO_{x}$ formation characteristics in the bluff-body stabilized flames.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.6
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• pp.171-178
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• 2006

The performance in the practical combustion system including reciprocating engines and gas turbine combustors is being much governed by turbulent reacting flow that is often analyzed by both a laminar flamelets concept and flame interaction. The characteristics of laminar flame interaction have been investigated numerically to provide basic understanding of wrinkled turbulent flames under concentration interaction resulting from inhomogeneity in fuel-air mixing, especially focused on the transition of flame characteristics such as diffusion flame, partially premixed diffusion flame, and triple-layer flame by the variation in the degree of premixedness. The extinction stretch rates to the premixedness have also been obtained in this paper. The boundary defining the regime of the existence of triple-layer flames as functions of both stretch rate and premixedness has been determined which agrees well with previously reported experiment measuring OH radical concentration peaks based on PLIF.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.3
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• pp.605-616
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• 2001

Generally, there are two methods in researching internal combustion engines. One is by experimental research and the other is by computer simulation. The experimental research has many merits that researchers can get data for engine performance, but it has also some demerit of cost and time. If there is an engine simulation code with accuracy for the solution, it is very convenient to predict the performance and optimum design value of the engine. In this study, engine performance simulation program has been improved to predict the transient variation of properties of gas in cylinder, intake and exhaust manifolds, There total program code was developed to calculate the pressure, flame factor and turbulent intensity, As a result of present study, the authors could predicted the in-cylinder pressure, intake manifold pressure and the engine performance in various conditions. The authors also could easily prepare the tool if optimum design of manifold and in-cylinder geometry.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.397-405
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• 2011

Hydrogen energy, as part of eco-friendly alternative energy, is made mostly through reforming of fossil fuels. The turbulent premixed combustion type of metal-fiber flat burner which is recently used in industry was tested in this paper. We measured the mean temperature distributions, CO, HC, $CO_2$ and $O_2$ concentrations to observe the flame structure and flame stability in some kind of experimental conditions. And also PIV and several flow analysis methods were compared to establish the numerical analysis model. The results of this paper will be the basis of the burner design of steam reformer.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.2
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• pp.22-31
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• 1997

We developed a general purpose program for the analysis of flows in the combustor with recirculating flow regime and simulated the flows. The program uses non-staggered grids based on finite volume method and the primitive variables are cartesian velocities. The combustion model is irreversible one step reaction with infinite chemistry The Favre averaged governing equations are considered and the clipped gaussian distribution is considered as a probability density function of the conserved scalar. We calculated turbulent diffusion flame with recirculating flow regime. Simulation shows two recirculating regions like experimental results. Velocity, turbulent kinetic energy, temperature and concentration distribution in simulation agree well with experimental data.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.201-202
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• 2012

The isothermal flow structure and mixing characteristics of a hybrid/dual swirl jet combustor for micro-gas turbine were numerically investigated. Location of pilot nozzle, angle and direction of swirl vane were varied as main parameters with constant fuel flow rates for each nozzle. As a result, the variation in location of pilot nozzle resulted in significant change in turbulent flow field near burner exit, in particular, center toroidal recirculation zone (CTRZ) as well as turbulent intensity, and thus flame stability and emission characteristics might be significantly changed. The swirl angle of $45^{\circ}$ provided similar recirculating flow patterns in a wide range of equivalence ratio (0.5~1.0). Compared to the co-swirl flow, the counter-swirl flow leaded to the reduction in CTRZ and fuel-air mixing near the burner exit and a weak interaction between the pilot partially premixed flame and the lean premixed flame. With the comparison of experimental results, it was confirmed that the case of co-swirl flow and swirl $angle=45^{\circ}$ would provided an optimized combustor performance in terms of flame stability and pollutant emissions.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.1-8
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• 2002

The flow and combustion patterns have been investigated inside the gasoline engine cylinder with the swirl or tumble flow, whereas the air flow characteristics, which are generated in the part of intake system before entering into the intake manifold, have not been known completely. It is necessary to analyze the flow field in the intake system consisting of air rater, throttle valve and intake manifold. The throttle valve, used to control the intake air flow rate, is important because it makes various mass flow rate and flow patterns. Three-dimen-sional How characteristics such as velocities, turbulent intensities and Reynolds shear stresses are measured by the hot wire anemometer at the exit of the throttle valve with the variation in the valve opening angle($15^{\circ}$, $45^{\circ}$, $75^{\circ}$ and $90^{\circ}$) and the Reynolds numbers (45000, 70000 and 140000). There are a lot of changes in flow characteristics at $75^{\circ}$ due to the large recirculation flow comparing with those of the other cases, and the streamwise velocity is especially enforced strongly below the valve shaft. The other component velocities are relatively large near the centerline parallel to the valve shaft. The effects of the Reynolds number on the flow field are not severe.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.5
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• pp.82-89
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• 1995

The three-dimensional fluid motion through the intake port and cylinder of a single DOHC SI engine was investigated with a commercial computational fluid dynamics simulation program, STAR-CD. This domain includes the intake port, intake valves and combustion chamber. Steady induction port flows for various valve lifts have been simulated for an actual engine configuration. The geometry was obtained by direct interface with a three-dimensional CAD software for complicated port and valve shape. The computational grid was generated using the commercial preprocessor ICEM CFD/CAE. Detailed procedures were presented on the generation of the geometry and the block-structured mesh. A standard k-${\varepsilon}$ turbulent model was applied to consider the complexity of the geometry and the fluid motion. The global flow patterns and the distributions of various quantities, such as pressure, velocity magnitude around the valve seat etc., were examined. The computational results, such as mass flow rate, discharge coefficient etc., for various valve lifts were compard with the experimental results and the computational results were found in good agreement with the experiment.

• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.286-294
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• 2006

Flows in a ramjet inlet is simulated for the study of the rocket-ramjet transition. The flow is unsteady, two-dimensional axisymmetric, compressible and turbulent. Double time marching method is used for the unsteady calculation and HLLC method is used as a higher order MUSCL method. As for turbulent calculation, $\kappa-\omega$ SST model is used for more accurate viscous calculations. Sinusoidal pressure perturbation is given at the exit and the flow fields at the inlet is studied. The cruise condition as well as the ground test condition are considered. The pressure level for the ground test condition is relatively low and the effect of the pressure perturbation at the combustion chamber is small. The normal shock at the cruise condition is very sensitive to the pressure perturbation and can be easily detached from the cowl when the exit pressure is relatively high. The sudden decrease in the mass flux is observed when the inlet flow becomes subcritical, which can make the inlet incapable. The amplitude of travelling pressure waves becomes larger as the downstream pressure increases, and the wavelength becomes shorter as Mach number increases. The phase difference of the travelling perturbed pressure wave in space is 180 degree.