• 한국분무공학회지
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• 제4권3호
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• pp.15-23
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• 1999

The use of LPG as clean fuel for Diesel engine is very attractive way to reduce soot and NOx emission. In this study, a numerical study has been done to know the transient behavior of LPG fuel in chamber pressures which is held at a pressure above (0.37MPa)and below(0.15MPa)the fuel vapor pressure. Results show that the vortex formed within the start of injection at the leading edge of the spray cone and was most apparent for 0.15MPa chamber pressure case. The high speed photographs and model results showed a narrower cone angle during the quasi-steady spray period at the 0.37MPa chamber pressure compared to the 0.15MPa case. And it can be shown that more realistic vaporization process is necessary to predict the spray length well.

• 설비공학논문집
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• 제12권10호
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• pp.925-931
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• 2000

Refrigerating ability of vapor compression refrigerator is decided by the harmonic work of it's components such as compressor, condenser, evaporator, expansion device, and so on. In this study, choosing refrigerant injectors as a new one of expansion device, temperature change of the cold room, ice freezing ability, and power consumption on flowrate of injector and refrigerant charging condition are evaluated experimentally. As the results of this study, it is verified that the spray injection type refrigeration system has some merits according to the flowrate and spray pattern of injector and charging quantum of refrigerant. And there are some design factors such as spray pattern and shape of spray chamber to utilize and fabricate this refrigerant injection type refrigerator.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.111-120
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• 2021

During the core disruptive accident (CDA) of sodium-cooled fast reactor (SFR), the molten fuel and steel are solidified into debris particles, which form debris bed in the lower plenum. When the boiling occurs inside debris bed, the flow of coolant and vapor makes the debris particles relocated and the bed flattened, which called debris bed relocation. Because the thickness of debris bed has great influence on the cooling ability of fuel debris in low plenum, it's very necessary to evaluate the transient changes of the shape and thickness in relocation behavior for CDA simulation analysis. To simulate relocation behavior, a large number of debris bed relocation experiments were carried out by improved bottom gas-injection experimental method in this paper. The effects of different experimental factors on the relocation process were studied from the experiments. The experimental data were also used to further evaluate a semi-empirical onset model for predicting relocation.

• 대한기계학회논문집
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• 제17권9호
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• pp.2339-2358
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• 1993

Since the rate and completeness of combustion in direct injection engines were controlled by the characteristics of gas flow fields and sprays, an understanding of those was essential to the design of the direct injection engines. In this study the numerical simulations of injection pressure effects on the characteristics of gas flow fields and sprays were preformed using the spray model that could predict the interactions between gas fields and spray droplets. The governing equations were discretized by the finite volume method and the modified k-.epsilon. model which included the compressibility effects due to the compression/expansion of piston was used. The results of the numerical calculation of the spray characteristics in the quiescent environment were compared with the experimental data. There were good agreements between the results of calculation and the experimental data, except in the early stages of the spray. In the motoring condition, the results showed that a substantial air entrainment into the spray volume was emerged and hence the squish motion was relatively unimportant during the fuel injection periods. It was found that as the injection pressure increased, the evaporation rate of droplets was decreased due to the narrow width of spray and the increased number of droplets impinged on the bottom of the piston bowl.

• 대한기계학회논문집
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• 제19권9호
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• pp.2373-2385
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• 1995

The goals of this study are to apply exciplex method to the visualization of the fuel spray of a diesel engine and to investigate the liquid phase of fuel spray that injected at the various tips of a fuel injector. This study provides the informations for the improvement of the diesel injection system and the structures of diesel spry with the boiling of fuel droplets in combustion chamber by the exciplex method. Hexame was used as fuel for approximation to injection condition of the engine. And naphthalene and TMDP were added to the fuel for the visualization by exciplex method. Experimental injectors were 4hole, 8hole, and 1hole impinging injectors. In the injection condition of actual engine the exciplex was sufficient to catch the liquid phase signal. The spray penetration of impinging injector was small than that of actual 4 and 8hole injector but atomization was better. The upper bound of impinging injector was determined by the geometry of a cylinder head and the lower bound was determined by spray angle. On impinging injector the atomization was better at the edge of disk than at center of disk and also the mixing with environmental gas was better.

• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.231-236
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• 2003

HCCI(Homogeneous Charge Compression Ignition) combustion is an advanced combustion process explained as a homogeneously premixed charge of a fuel where air is admitted into the cylinder and compression ignited. It has possibility to reduce NOx by spontaneous auto-ignition at multiple points that allows very lean combustion resulting in low combustion temperatures. Particulate matters (PM) could be also reduced by the homogeneous combustion and no fuel-rich zones. Injection timing is extremely advanced to achieve homogeneous charge where a diesel fuel could not be vaporized sufficiently due to low pressure and low temperature condition. Also the over-penetration could be a severe problem. The small injection angle and multi-hole injectors were applied to solve these problems. Dimethyl ether (DME) as an altenative fuel was also applied to relive the bad vaporization problem associated with early injection of diesel fuel. Neat DME has a very high cetane rating and high vapor pressure. Contained oxygen reduces soot during the combustion. Experimental result shows DME can be easily operated in an HCCI engine. PM shows almost zero value and NOx is reduced more than 90% compared to direct-injection diesel engine operating mode but problem of early ignition needs more investigation.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.30-39
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• 2001

The direct injection into the cylinders has been regarded as a way of the reduction in fuel consumption and pollutant emissions. The spray produced by the high pressure injector is of paramount importance in DISI(Direct Injection Spark Ignition) engines in that the primary atomization process must meet the requirement of quick and complete evaporation, mixing with air and combustion especially to prohibit the excessive HC emissions. The interaction between air flow and fuel spray was investigated in a steady flow system embodied in a wind tunnel to simulate the variety of flow inside the cylinder of the DISI engine. The direct Mie scattered and shadowgraph images presented the macroscopic view of the liquid sprays and vapor fields. The velocity and particle size of fuel droplets were investigated by phase doppler anenometer(PDA) system. The processes of atomization and evaporation with a DISI injector were observed and consequently utilized to construct the data-base for the spray and fuel-air mixing mechanism as a function of the flow characteristics.

• 한국분무공학회지
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• 제28권1호
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• pp.32-42
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• 2023

In this study, spray characteristics of n-heptane and propane were investigated under different injection pressure using various imaging techniques such as Mie-scattering, DBI (diffuse back-illumination), and Schlieren imaging techniques. NI compact RIO system was used to control a test injector. Spray penetration length, length-to-width ratio and number of black pixels were calculated by using MATLAB software to compare spray characteristics of each fuel. Longer spray penetration length and higher length-to-width ratio were observed in propane spray because of flash boiling caused by high saturated vapor pressure. Spray collapse occurred in propane spray due to the high plume-to-plume interaction. Moreover, rapid evaporation occurred in propane spray, so that nozzle tip wetting could not be observed. Rapid evaporation of propane also caused fewer residual droplets compared to n-heptane spray. Therefore, propane is advantageous in reducing the generation of soot emission from large droplets that are not atomized. However, additional evaluation should be conducted considering combustion efficiency and the possibility of deposits by nozzle tip icing during fuel injection.

• 한국수소및신에너지학회논문집
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• 제27권6호
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• pp.727-736
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• 2016

Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

• Composites Research
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• 제18권5호
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• pp.27-33
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• 2005

본 연구에서는 펄스-CVI (Chemical Vapor Infiltration)에 의해 탄화규소/탄소 복합재료를 제조하는 공정에 대한 수치모사가 행해졌다. 각 펄스가 가스 주입시간, 반응시간, 배출시간으로 구성될 때, 반응시간과 배출시간의 영향이 관찰되었다. 또한 반응가스 농도와 압력의 영향이 연구되었다. 탄소프리폼에의 탄화규소의 균일한 침착과 반응시간 단축을 위한 펄스-CVI공정의 이점이 확인되었다.