• Journal of the Korean Society of Combustion
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• v.7 no.1
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• pp.44-51
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• 2002

This paper presents an atomization model for sprays under flash boiling conditions. The atomization is represented by the secondary breakup of a bubble/droplet system, and the breakup is considered as the results of two competing mechanisms, aerodynamic force and bubble growth. The model was applied to predict the atomization of a hollow-cone spray from pintle injector under flash boiling conditions. In the regimes this study considered, sprays are atomized by bubble growth, which produces smaller SMD#s than aerodynamic forces alone. With decreasing ambient pressures, the spray thickness, fuel vaporization rate and vapor radial penetration increases, and the drop size decreases. With increasing the fuel and ambient temperatures to some extent, the effect of flash boiling and air entrainment completely change the spray pattern.

• Journal of ILASS-Korea
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• v.2 no.1
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• pp.18-28
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• 1997

The present study is mainly aiming at numerically analyzing the combustion and emission characteristics of the diesel spray in a high-pressure environment. Computations are peformed for the peak chamber pressure with range from 4.08 MPa to 162 MPa. Numerical results indicate that the pressure increase in combustion chamber significantly influences the mechanism for droplet dynamics and mixing characteristics, spray penetration autoignition, flame lift-on height and the propagation or fuel vapor and flame. By increasing the ratio or the ambient density to injected liquid density, the fuel-air mixing rates and the burning rates increase and the $NO_x/soot$ emission level decreases.

• Journal of ILASS-Korea
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• v.13 no.2
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• pp.91-98
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• 2008

In the present study, in order to understand the overall spray combustion characteristics of DME fuel as well as to identify the distinctive differences of DME combustion processes against the conventional hydrocarbon liquid fuels, the sequence of the comparative analysis have been systematically made for DME and n-heptane liquid fuels. To realistically represent the physical processes involved in the spray combustion, this studyemploys the hybrid breakup model, the stochastic droplet tracking model, collision model, high-pressure evaporation model, and transient flamelet model with detailed chemistry. Based on numerical results, the detailed discussions are made in terms of the autoignition, spray combustion processes, flame structure, and turbulence-chemistry interaction in the n-heptane and DME fueled spray combustion processes.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.999-1008
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• 2002

The spray structures and distribution characteristics of liquid and vapor phases in non-evaporating and evaporating Gasoline Direct Injection (GDI) fuel sprays were investigated using Laser Induced Exciplex Fluorescence (LIEF) technique. Dopants were 2% fluorobenzene and 9% DEMA (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to study internal structure of the spray, droplet size and velocity under non-evaporating condition were measured by Phase Doppler Anemometry (PDA). Liquid and vapor phases were visualized at different moments after the start of injection. Experimental results showed that the spray could be divided into two regions by the fluorescence intensity of liquid phase: cone and mixing regions. Moreover, vortex flow of vapor phase was found in the mixing region. About 5㎛ diameter droplets were mostly distributed in the vortex flow region. Higher concentration of vapor phase due to vaporization of these droplets was distributed in this region. Particularly, higher concentration of vapor phase and lower one were balanced within the measurement area at 2ms after the start of injection.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.126.1-126.1
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• 2015

A quantitative relationship between Leidenfrost point and surface characteristics such as surface material and roughness is investigated. Based on the relationship, we have fabricated the surfaces with their Leidenfrost points (LFP) tuned by controlling surface coating and structures. As discovered by Leidenfrost, liquids placed on a hot plate levitate on the gas phase-air gap formed by the vaporization of liquids. This phenomenon is called 'Leidenfrost effect'. A change of LFP has attracted many researchers for several years but the ability to tune LFP is still a remaining issue. Many of previous work has progressed for various conditions so the systematic approach and analysis are needed to clearly correlate the LFP and the surface conditions. In this report, we investigate a relation of surface energy and LFP using various coating materials such as Octadecyltrichlorosilane (OTS) and 1H, 1H, 2H, 2H-Perfluorooctyltrichlorosilane (FOTS). Also, we analyze how surface roughness affects LFP via surface micro structuring with ICP-RIE fabrication process. The improved understanding can have potential applications such as the control of liquid droplet behavior at elevated temperatures for efficient cooling system.

• Journal of ILASS-Korea
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• v.9 no.2
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• pp.9-17
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• 2004

The performance characteristics of lean burn system in gasoline engine are mainly affected by the air-fuel mixture in cylinder, gas exchange process of manifold system, exhaust emission of engine, and the electronic engine control system. In order to obtain the effect of performance factors on the optimum conditions of lean burn engine, this study deal with the behavior of mixture formation, gas flow characteristics of air, flow and evaporation analysis of spray droplet in cylinder, vaporization and burning characteristics of lean mixture in the engine, and the control performance of electronic engine control system. The optimum flow conditions were investigated with the swirl and tumble flows in the combustion chamber with swirl control valve. The performance characteristics and optimum condition of flow field in intake system were analyzed by the investigation of inlet flow of air and combustion stabilization on cylinder.

• Journal of Institute of Convergence Technology
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• v.8 no.1
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• pp.9-13
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• 2018

The purpose of this study is to investigate the liquid- and vapor-phase spray characteristics, such as spray tip penetration and spray angle using gasoline direct injection (GDI) injector with multi-hole. The vapor-phase spray was captured by the Schlieren visualization system, which consists of high-speed camera, LED lamp, concave mirrors, and knife-edge. The liquid-phase spray was visualized by Mie-scattering techniques. Both spray images of vapor- and liquid-phase were visualized under 373 K of ambient temperature, 1 bar of ambient pressure, and 100/200 bar of injection pressure. The energizing duration was fixed at 1.5 ms. From the analysis of experimental results, it revealed that the increased injection pressure induced an early vaporization due to the improvement of droplet atomization. The spray tip penetration and spray angle in vapor-phase were higher than those in liquid-phase. The difference in the spray tip penetration between vapor- and liquid-spray gradually increased with the time elapsed after the injection. Even with the spray angle characteristics, it was found that the difference between the spray angle of liquid and vapor spray gradually grew after they entered steady-state conditions.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.265-276
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• 1994

Several improvements to the RELAP5/MOD3 reflood model hate been made. These improvement were made to correct deficiencies in the reflood model identified by the assessment of the RELAP5/MOD3 code against FLECHT-SEASET experiments. The improvements consist of modification of reflood wall heat transfer package and adjusting the droplet size in dispersed flow regime. The time smoothing of wall vaporization and level tracking of transition flow are also added to eliminate the pressure spikes and level oscillation during reflood process. Assessment of the improved model against FLECHT-SEASET experimental data and application of LBLOCA analysis for plant shows that the deficiencies have been corrected.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.233-236
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• 2009

In this study, the characteristic of the hybrid rocket motor with $LN_2O$(Liquid Nitrous oxide) was investigated experimentally. HDPE(High Density PolyEthlene) was used as fuel with different sized single port. When used $LN_2O$, combustion efficiency is lower than using $GN_2O$(Gas Nitrous oxide), because of completeness of vaporization of droplet and mixing. And regression rate was changed by different oxidizer phase. This behavior was considered that flame temperature and combustion of solid fuel front/end surface.

• Journal of ILASS-Korea
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• v.14 no.4
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• pp.147-152
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• 2009

Since a liquid-phase LPG injection system allows accurate control of fuel injection and increase in volumetric efficiency, it has advantages in achieving higher engine power and lower emissions compared to the mixer type LPG supplying system. However, this system also leads to an unexpected event called icing phenomenon which occurs when moisture in the air near the injector freezes and becomes frost around the nozzle hole due to extraction of heat from surrounding caused by instant fuel vaporization. As a result, it becomes difficult to control air/fuel ratio in engine operation, inducing exacerbation of engine performance and HC emission. One effort to mitigate icing phenomenon is to attach anti-icing injection tip in the end of nozzle. Therefore, in this study, the effect of engine operation parameters as well as surrounding conditions on icing phenomenon was investigated in a bench test rig with commercially-used anti-icing injection tips. The test results show that considerable ice was deposited on the surface near the nozzle hole of the anti-icing tip in low rpm and low load operating conditions in ambient air condition. This is because acceleration of detachment of deposited ice from the tip surface was induced in high load, high rpm conditions, resulting in decrease in frost accumulation. The results of the bench testing also demonstrate that little or no ice was formed at surrounding temperature below a freezing point since the absolute amount of moisture contained in the intake air is too small in such a low temperature.