• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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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.

• 대한기계학회논문집
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• 제12권3호
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• pp.534-540
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• 1988

본 연구에서는 디이젤분무 주위기체의 유동특성중에서 유동속도에 관하여 보 고 하였다. 본모에서는 분무기간중 분사압력의 시간경과특성이 상이한 두 종류의 분 사계를 사용하여 생성된 분무와 주위 기체와의 유동방향의 시간경과 및 유입시기, 정 상유입속도 도달시간등을 분무의 축방향과 반경방향에 대하여 상세한 측정결과를 얻었 기에 보고한다.

• 한국분무공학회지
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• 제20권4호
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• pp.261-267
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• 2015

The main purpose of this study is to provide the information of soot generation of toluene fuel droplet. To achieve this, this paper provides the experimental results on the different initial diameter of toluene droplet combustion characteristics conducted under equivalent ambient pressure ($P_{amb}$) and oxygen concentration ($O_2$) conditions. Visualization of single fuel droplet was performed with high resolution CCD camera and visualization system. At the same time, ambient pressure ($P_{amb}$) and oxygen concentration ($O_2$) were maintained by ambient condition control system. Soot volume fraction ($f_v$) was analyzed and compared on the basis of intensity ratio ($I/I_0$) of background image. The result of soot generation was almost the same regardless of initial droplet diameter since thermophoretic flux is not much changed under the same ambient conditions. Soot standoff ratio (SSR) of 2 mm diameter showed unstable variation characteristics due to the short available measuring time.

• 한국분무공학회지
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• 제22권2호
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• pp.80-86
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• 2017

The soot formation characteristics of various alkane-based single fuel droplets were studied in this work. Also, This study was performed to provide the database of the soot behavior and formation of alkane-based single fuel droplet. The experimental conditions were set to 1.0 atm of ambient pressure ($P_{amb}$), 21% of oxygen concentration ($O_2$) and 79% of nitrogen concentration ($N_2$). Combustion and soot formation of single fuel droplet was visualized by visualization system with high speed camera. At the same time, ambient pressure, oxygen concentration and nitrogen concentration were maintained by ambient condition control system. Soot formation characteristics was analyzed and compared on the basis of intensity ratio ($I/I_0$) of background image. The results of toluene fuel droplet showed the largest soot generation. Soot volume fraction ($f_v$) was almost the same under the identical fuel types regardless of various initial droplet diameter ($d_0$) since thermophoretic flux was not much changed under the same ambient conditions.

• 대한기계학회논문집B
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• 제26권8호
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• pp.1138-1144
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• 2002

Recently GDI(Gasoline Direct Injection) engine is spot-lighted to achieve higher thermal efficiency under partial loads and better performance at full loads. To realize this system, it is essential to make both stratified combustion and homogeneous combustion. Spray pattern must be optimized according to injection timing because ambient pressure in combustion chamber is varied with crank angle. In this experimental study, two types of visualization system such as laser scattering method and schlieren method were developed to clarity the spray behavior during on intake stroke. As the ambient pressure increases, thepenetration length and spray angle show a tendancy to decrease due to rising resistance caused by the drag force of the ambient air. Distribution of injected fuel on intake stroke has a significant effect on homogeneous mixture in the cylinder. These results provide the information on macroscopic wall-wet growth in the cylinder and design factors for developing GDI injector.

• 동력기계공학회지
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• 제14권6호
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• pp.5-12
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• 2010

In this study, an analysis of evaporative diesel spray and an usefulness of a general-purpose program, ANSYS CFX release 11.0, are investigated through the comparison and investigation of the experimental results carried out under an evaporative field, in which there is phase transition, by an exciplex fluorescence method and the results analyzed by the CFX program. The diesel fuel called n-Tridecane, $C_{13}H_{28}$, is injected from a single-hole nozzle (l/d=1.0mm/0.2mm) into a constant volume chamber under a high temperature and pressure. In the same condition as the experimental condition, the analysis was carried out. Both results of the spray tip penetration were almost coincident at each time. The results have validated the usefulness of this analysis. As a result, if the ambient pressure is high, the spray tip penetration will be shortened and move toward the nozzle exit.

• Applied Microscopy
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• 제43권1호
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• pp.34-39
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• 2013

Glandular and nonglandular trichomes on the leaf surface of Plectranthus tomentosa were investigated by variable pressure field emission scanning electron microscopy (VP-FESEM). The segments of the plant's leaves were directly mounted without any specimen preparation, and examined at ambient temperature using a variable pressure secondary electron (SE) detector under ca. 15 Pa. Foliar trichomes maintained their shapes and structures without severe surface collapse or charging. The adaxial leaf surface was abundantly covered with different types of trichome. Nonglandular trichomes consisted of a basal cell and a long (up to ca. $300{\mu}m$) stalk. Meanwhile, capitate glandular trichomes had a secretory head and a short or long stalk. Peltate glandular trichomes with globose secretory heads were observed in close contact with the leaf epidermis. Spherical projections on the secretory head showed the secretion process of glandular trichomes. In addition to the trichomes, oval stomata were distributed on the abaxial leaf surface. These results suggest that ambient VP-FESEM can be used to classify the dehydration-sensitive foliar trichomes of succulent plants by SE imaging. At the FESEM resolution, this approach facilitates the rapid and detailed morphological analysis of a variety of trichomes in diverse plant taxa with reduced labor and preparation.

• 한국분무공학회지
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• 제6권1호
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• pp.25-34
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• 2001

Several efforts to meet the exhaust gas regulation have been undertaken by many researchers in recent years. Main researches are on development of design techniques of intake port and combustion chamber, atomisation of fuel and precise control of air-fuel ratio, post-treatment of exhaust gas and so on. Engine technology is changed from PFI to GDI to correspond with exhaust gas regulation. GDI technique makes it possible to preserve lean air-fuel ratio and control accurate air-fuel ratio. Nevertheless, It is not cleared that information of spray characteristics and atomization process are very dependent on fluctuation of pressure and change of temperature in intake stroke. In this study, a constant volume combustion chamber is manufactured to investigate various fluctuations of in-cylinder pressure for injection duration. It is taken photographs of injection process of conventional GDI injector using PMAS. Then, it was verified experimently that ambient conditions as temperature and pressure of combustion chamber have effects on process of spray growth and atomization of fuel.

• Bulletin of the Korean Chemical Society
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• 제22권11호
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• pp.1273-1276
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• 2001

• 한국전기전자재료학회논문지
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• 제22권12호
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• pp.1078-1083
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• 2009

Generally Lighting system consists of lamp and luminaire. When a fluorescent lamp is installed in luminaire, power and light output is changed by ambient temperature. Particularly electrodeless lamp depends on the changes that are mercury pressure with amalgam temperature and magnetic properties with ferrite temperature. It has finally influence on optical efficiency. In this study, the temperature change of ferrite and cold spot, vessel are measured at transitional state and then same characteristics are measured with increase of ambient temperature. At transitional state, luminous flux is related to temperature change of cold spot that compare with behavior of mercury pressure and light output. At increase of ambient temperature, we analyzed change that efficiency and electrical, optical characteristics of elecrodeless lamp are related to ferrite core and cold spot temperature.