• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.157-163
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• 2003

A systematic numerical experiment has been conducted to study droplet gasification in high pressure environments with pressure oscillations. The general frame of previous rigorous model[1] is retained but tailored for flash equilibrium calculation of vapor-liquid interfacial thermodynamics. Time-dependent conservation equations of mass, momentum, energy, and species concentrations are formulated in axisymmetric coordinate system for both the droplet interior and ambient gases. In addition, a unified property evaluation scheme based on the fundamental equation of state and empirical methods are used to find fluid thermophysical properties over the entire thermodynamic domain of interest. The governing equations with appropriate physical boundary conditions are numerically time integrated using an implicit finite-difference method with a dual time-stepping technique. A series of calculation have been carried out to investigate the gasification of an isolated n-pentane droplet in a nitrogen gas environment over a wide range of ambient pressures and frequencies. Results show that the mean pressures and frequencies of the ambient gas have strong influences on the characteristics of the droplet gasification. The amplitude of the response increases with increasing pressure, and the magnitude of the vaporization response increases with the frequency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.392-398
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• 2009

Theoretical thrust equations for the diverse nozzle expansion condition were derived. By using the obtained thrust equations, parametric studies were carried out to estimate the effect of pressure exponent, minimum operation pressure, ambient pressure and extinguishment pressure on thrust modulation performance in pintle-nozzle solid rocket motors. Analysis results showed that thrust turndown ratio can be easily attained by small nozzle-throat area variation at high pressure exponent, low minimum operation pressure, high ambient pressure and high extinguishment pressure condition. At those conditions, the highest chamber pressure to obtain the intended thrust turndown ratio can be minimized.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.2
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• pp.50-58
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• 2001

The purpose of this research is to obtain the information of the development process of a vaporizing GDI spray using exciplex fluorecence method. Fluorobenzene/DEMA system was used as the exciplex-forming dopants. The 2-D spray images of liquid and vapor phases were acquired, and the behavior of both phases was analyzed by the image processing. The experiment was performed at the three different ambient perssures and the ambient temperature of 273K and 473K. As the result of this work, it was found that the development characteristics of GDI spray have stronger effect on the ambient pressure than on the ambient temperature. With an increase of ambient pressure, the distribution of vapor phase was decreased and the concentration of that was denser. Two regions, namely cone and mixing regions could be identified from those resulrs.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.55-65
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• 1999

An experimenta investigation of unsteady impinging DI diesel spray on the unheated plate and heated plate has been conducted in a pressurized chamber using high speed shadowgraphy. The ambient agas pressure was varied using nitrogen with chamber pressure of 1.1MPa, 2.1MPa and 2.6MPa. As the increase of ambient gas pressure of ambient gas pressure, the height of spray is increased if entrainment and circulation . At higher temperature of impinging plate, the radial penetration of the impinging spary is incresed , but the height of impinging spray is decreased.

• Journal of ILASS-Korea
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• v.19 no.1
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• pp.1-8
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• 2014

Liquefied petroleum gas (LPG) is regarded as an alternative fuel for spark ignition engine due to similar or even higher octane number. In addition, LPG has better fuel characteristics including high vaporization characteristic and low carbon/hydrogen ratio leading to a reduction in carbon dioxide emission. Recently, development of LPG direct injection system started to improve performance of vehicles fuelled with LPG. However, spray characteristics of LPG were not well understood, which is should be known to develop injector for LPG direct injection engines. In this study, effects of operation condition including ambient pressure, temperature, and injection pressure on spray properties of n-butane were evaluated and compared to gasoline in a multi-hole injector. As general characteristics of both fuels, spray penetration becomes smaller with an increase of ambient pressure as well as a reduction in the injection pressure. However, it is found that evaporation of n-butane was faster compared to gasoline under all experimental condition. As a result, spray penetration of n-butane was shorter than that of gasoline. This result was due to higher vapor pressure and lower boiling point of n-butane. On the other hand, spray angle of both fuels do not vary much except under high ambient temperature conditions. Furthermore, spray shape of n-butane spray becomes completely different from that of gasoline at high ambient temperature conditions due to flash boiling of n-butane.

• Journal of ILASS-Korea
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• v.7 no.3
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• pp.18-23
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• 2002

An evaporating diesel spray of a common rail lnjector was visualized by LIEF technique. This technique makes it possible to separate the vapor and liquid phase images. The experiment was conducted in a constant volume vessel to make a high temperature and high pressure condition. Three images(vapor and liquid phase images from LIEF and a liquid phase image from Mie scattering) were taken simultaneously in one spray event. The major experimental parameters are the injection pressure and the ambient gas pressure. Also, a relative SMD distribution in a liquid phase was obtained by the ratio of the intensities of the fluorescence and the Mie scattering. The results show that the injection pressure and the ambient gas pressure have a close relation with the spray development and air-fuel muting process.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.3
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• pp.44-50
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• 2004

The purpose of this study is to improve the prediction ability of the atomization and vaporization processes of GDI spray under high-pressure and high-temperature conditions. Several models have been introduced and compared. The atomization process was modeled using hybrid breakup model that is composed of Conical Sheet Disintegration (CSD) model and Aerodynamically Progressed TAB(APTAB) model. The vaporization process was modeled using Spalding model, modified Spalding model and Abramzon ＆ Sirignano model. Exciplex fluorescence method was used for comparing the calculated with the experimental results. The experiment and calculation were performed at the ambient pressure of 0.5 MPa and 1.0 MPa and the ambient temperature of 473k. Comparison of caldulated and experimental spray characteristics was carried out and Abramzon ＆ Sirignano model and modified Spalding model had the better prediction ability for vaporization process than Spalding model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.7
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• pp.97-104
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• 2006

The spray and breakup characteristics of swirling liquid sheet were investigated by measuring the spray angle and breakup length as the axial Weber number Wel was increased up to 1554 and the ambient gas pressure up to 4.0MPa. As Wel and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces, and thus the liquid sheet disintegrated near from the injector exit. The measured spray angles according to the ambient gas density were different before and after the sheet breaks. Before the liquid sheet breaks, the spray angle was almost constant, but once the liquid sheet started to breakup, the spray angle decreased. And the breakup length decreased because of the increase of the aerodynamic force as the ambient gas density and Wel increased. Lastly, the measured breakup length according to the ambient gas density and Wel was compared with the result by the linear instability theory. We found that the corrected linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• Journal of ILASS-Korea
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• v.20 no.3
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• pp.187-194
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• 2015

In this study, three visualization methods, Schlieren, Shadowgraph, and Mie-scattering, were applied to compare diesel and gasoline spray structures. Fuels were injected into a high pressure/high temperature constant volume chamber under the same ambient pressure and temperature condition of low load in gasoline direct injection compression ignition (GDCI) engine. Two injection pressures (40 and 80 MPa), two ambient pressures (4.2 and 1.7 MPa), and two ambient temperatures (908 and 677 K) were use. The images from the different methods were overlapped to show liquid and vapor phases more clearly. It was found that the gasoline fuel is more appropriate to form a lean mixture.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.1-6
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• 1999

An experimental study was carried out to investigate the global spray behavior and spray characteristics of high-pressure fuel injector in the direct-injection goasoline enginet. The atomization characteristics of fuel spary such as mean droplet size, mean velocity , and velocity distribution were measured by the phase Doppler particle analyzer. The spray tip penetration and spray width were investigated by the result fo visualizaiton experiment. The quantitiative spary characteristics of injector spray were measured under various sparay conditions and ambient pressures. The results of experiment show that the increase in ambient pressure have influence on the spray tip penetration and spray development process. Also, the influence of injection pressure and measuring location on the mean velocity and droplet size distribution were discussed.