• International Journal of Automotive Technology
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• v.5 no.3
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• pp.181-188
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• 2004

A cylindrical constant-volume combustion chamber was used to investigate the flow characteristics at the spark electrode gap and the combustion characteristics of an inhomogeneous charge methane-air mixture under several parameters such as stratified pattern, initial charge pressure, ignition time and the excess air ratio of the initial charge mixture. Flow characteristics including mean velocity and turbulence intensity were analyzed by a hot-wire anemometer. The combustion pressure development, measured by a piezo-electric pressure transducer, was used to investigate the effect of initial charge pressure, excess air ratio and ignition times on combustion pressure and combustion duration. It was found that the mean velocity and turbulence intensity had the maximum value around 200-300 ms and then decreased gradually to near-zero value at 3000 ms. For the stratified patterns, the combustion rate under the rich injection (RI) condition was the fastest. Under the initial charge conditions, the second mixture was accompanied by an increase in the combustion rate, and that the higher the mass which is added in the second stage injection, the faster the combustion rate.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.228-236
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• 2012

Large eddy simulation (LES) is increasingly used as a tool for studying the dynamics of turbulence in combustion chamber flows due to the promise of wider generality and more accurate results compared to Reynolds averaged Navier-Stokes(RANS) models. This study presents the appropriate subgrid-scale(SGS) model in LES for predicting the turbulent flow field in the internal combustion engine. The study of the effects of model and numerical parameters such as discretization scheme, initial condition, time step and SGS model was performed. The results of LES using the SGS model were found to be in the good agreement with experimental data.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.6
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• pp.1020-1033
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• 2015

In order to design a compact urea selective catalytic reduction system, numerical simulation was conducted by computational fluid dynamics tool. A swirl type static mixer and a mixing chamber were considered as mixing units in the system. It had great influence on flow characteristics and urea decomposition into ammonia. The mixer caused flow recirculation and high level of turbulence intensity, and the chamber increased residence time of urea-water-solution injected. Because of those effects, reaction rates of urea decomposition were enhanced in the region. When those mixing units were combined, it showed the maximum because the recirculation zone was significantly developed. $NH_3$ conversion was maximized in the zone due to widely distributed turbulence intensity and high value of uniformity index. It caused improvement of $NO_x$ reduction efficiency of the system. It was possible to reduce 55% length of the chamber and connecting pipe without decrease of $NO_x$ reduction efficiency.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.3
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• pp.10-18
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• 2004

It is well known that the stratified charge combustion has many kind of advantages to combustion characteristics, such as higher thermal efficiency and less CO, NOx levels than conventional homogeneous mixture combustion. Although this combustion can be caused low fuel consumption, it is produced the high unburned hydrocarbon and soot levels because of different equivalence ratio in the combustion chamber. Moreover it has a lot of possibility of low output and misfire if the mixture gas would not be in existence around the spark plug. In this paper, fundamental studies for stratified combustion were carried out using a constant volume combustion chamber. The effect of locally mixture gas distribution according to control the direct injection and premixed injection in the chamber were examined experimentally. In addition, the effects of turbulence on stratified charge combustion process were observed by schlieren photography.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.1
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• pp.11-17
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• 2007

Effects of combustion chamber design on combustion stability characteristics of a full-scale gas generator were studied experimentally. Thirty seven double-swirl injectors with recess number of 1.5 were distributed in the injector head, which significantly influences combustion performance. The characteristics of combustion stability were inspected by the parametric variations such as changing length and diameter of the combustion chamber and installing a turbulence ring. The experimental result shows that as the effective length of the combustion chamber decreased, an instability frequency took place in a high-frequency region, and the amplitude of the dynamic pressure generally diminished and could be reduced to the unharmful level. However, the dynamic pressure fluctuation in the region of longitudinal resonant frequency could not be suppressed perfectly.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.244-254
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• 1996

Flow velocity was measured by, use of hot wire anemometer. Turbulence intensity was in proportion to mean flow velocity regardless of swirl velocity. And integral length scale has proportional relation with swirl velocity regardless of measurement position. Turbulent burning speed during flame propagation which was determined by flame photograph and gas pressure of combustion chamber was increased with the lapse of time from spark and was decreased a little at later combustion period. Because of combustion promotion effect, turbulent burning speed was increased according to increase of turbulence intensity. Burning speed ratio i.e. ratio of turbulent burning speed ($S_BT$) to laminar burning speed ($S_BL$) was found out by use of turbulence intensity u' and integral length scale $l_x$ , $\delta_L$ is width of preheat zone in laminar flame.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.391-398
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• 2008

LES analysis was conducted with in-house CFD code to investigate the turbulence evolution and interaction due to turbulence ring and splash plate in the gas generator. Though chemical reaction was not accounted for, the results can be useful in determining the turbulence characteristics generated by ring and plate. The calculation results show that the installation of turbulence ring can introduce additional turbulences and improve turbulent mixing in the downstream flow. However, the addition of splash plate in the downstream of TR brings totally different shape of perturbation energy and enstrophy distribution for turbulent mixing. This enhancement can be done by the formation of the intensively strong vorticity production and mixing behind the plate. Pressure drop was found to be a reasonable level of about 1% or less of initial pressure in all calculation cases. Also, calculation results revealed that the variation of TR shape and intrusion length did not change the characteristics of turbulent mixing in the chamber. Even though the effect of installation location of splash plate on the turbulent mixing is not investigated yet, calculation results conclude the addition of splash plate leads to the increase in turbulent mixing with an acceptable pressure drop.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.5
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• pp.480-488
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• 2020

This study was conducted to improve the flow uniformity inside the chip tester through changing the flow path formation according to the inlet and outlet position of chamber. The internal flow and velocity distributions of the modified chamber models (Cases 1-3) were compared with the reference chamber model through three-dimensional Reynolds-averaged Navier-Stokes equations with k-ε turbulence model. The modified chamber models showed the superior flow uniformity characteristics compared to the reference chamber model. To investigate the flow uniformity in the chip tester, the standard deviation of the velocity was defined and compared. Through the internal flow analysis and assesment of the standard deviation, Case 2 among the test cases including the reference model showed the best flow uniformity generally.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.1
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• pp.48-53
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• 2000

The effects of the internal flow in a diesel injection nozzle on the atomization of the spray has been investigated experimentally. Flow visualization was made using a transparent acrylic model nozzle. And also, measurement of the sac chamber pressure was made for clartfying the effect of pressure fluctuation in the sac chamber on the wpray behaviors. The geometry of the model nozzle was scaled up 10 times of the actual nozzle and the injection pressure for the model nozzle was adjusted so as to achieve a Reynolds number at the discharge hole which was the same as the actual nozzle. Polystyrene tracers, a laser sheet light and a still/high speed video camera were used to visualize the flow pattern in the sac chamber. When the needle lift was small, the high turbulence in the sac chamber generated by the high velocity seat flow made the spread angle of the spray large. Cavitation which arose in the sky chamber induced the pressure fluctuation and then affects the spread angle of the spray.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.905-913
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• 2006

The instability curve of a Rijke tube system was obtained accurately by following different paths of heat power and flow-rate for three regions and by defining its locus from the criterion based on the measured sound pressure levels. The unstable limits in the region of flow-rate lower than that at the minimal power are compared with previous data. To observe the effect of turbulence on the unstable limits, inflow turbulence was introduced by placing a bundle of circular cylinders upstream of the heating part ($50). The large-amplitude inflow fluctuation may delay the transition of the chamber acoustic mode to the unstable Bone even at a sufficient power.