• 한국분말재료학회지
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• 제16권6호
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• pp.403-409
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• 2009

Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500$^{\circ}C$ promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.

• 한국자동차공학회논문집
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• 제11권2호
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• pp.56-62
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• 2003

Spray characteristics of conventional diesel fuel and bio-diesel fuel(methyl-ester of soybean oil) were compared, in terms of spray tip penetration and spray angle, by using a commercial high pressure common rail injection system for light-duty DI Diesel engines. The experiments were carried out under the non-evaporating condition at ambient density(8.8, $15.6 kg/\textrm{m}^3$) and injection pressure(75, 135 MPa). The experimental method was based on a laser sheet scattering technique. Spray tip penetrations of bio-diesel fuel were longer, on the whole, than those of conventional diesel fuel, except for lower injection pressure(75 MPa) under lower ambient density$(8.8 kg/\textrm{m}^3)$. But spray near angle and spray far angle of bio-diesel fuel were smaller than those of conventional diesel fuel, implying spray angle is related to the growth rate of spray tip penetration. The experimental results of spray tip penetration agreed well with the calculated values by the Wakuri et al.'s correlation based on the momentum theory.

• 한국분무공학회지
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• 제17권3호
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• pp.121-127
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• 2012

The study is to investigate the mixing stability, fuel properties, and macroscopic spray characteristics of diesel-gasoline blended fuels in a common-rail injection system of a diesel engine. The test fuels were mixed diesel with gasoline fuel, which were based volume fraction of gasoline from 0 to 100% in 20% intervals. In order to analyze the blended effect of gasoline to diesel fuel, the properties of test fuels such as density, viscosity, and surface tension were measured. In addition, the spray behavior characteristics were studied by investigating the spray tip penetration and spray angle using a spray images through a spray visualization system. It was revealed that the density, kinematic viscosity and surface tension of diesel-gasoline blending fuels were decreased with the increase of gasoline fuel. The injection quantity of test fuels were almost similar level at short energizing duration condition. On the other hand, the increase of energizing duration shows the decrease of injection quantity compared to short energizing duration. The test blending fuels have similar growth in Spray tip penetration and Spray cone angle.

• 대한기계학회논문집B
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• 제33권3호
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• pp.201-206
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• 2009

The focus of this work is placed on the analysis of the mixture formation process under the evaporative diesel-free spray conditions. In order to examine homogeneity of mixture within the vapor phase region of the injected spray, image analysis was carried out based on the entropy of statistical thermodynamics. As an experimental parameter, the injection pressure and ambient gas density were selected, and effects of the injection pressure and density variation of ambient gas on the mixture formation process in the evaporative diesel spray were investigated. In the case of application of the thermodynamic entropy analysis to evaporative diesel spray, the value of the dimensionless entropy always increases with increase in time from injection start. Consequently, the dimensionless entropy in the case of the higher injection pressure is higher than that of lower injection pressure during initial injection period.

• 수산해양기술연구
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• 제52권1호
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• pp.65-71
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• 2016

Injection rate, injection quantity and injection timing of fuel are controlled precisely by electric control in CRDI system. Particularly, injection rate being influenced with injection pressure affects to spray characteristics and fuel-air ratio, so it is a very important factor in diesel combustion. In this study, injection rates in accordance with injection pressure at a constant ambient pressure were measured with Zeuch's method. Under the same condition, non-evaporating spray images were taken with a high speed camera and analyzed carefully with Adobe Photoshop CS3. Macroscopic spray characteristics and breakup processes in the spray could be found from the examined and analyzed data. Injection start time and injection period were practically affected with injection pressure. Also, initial injection rate, spray penetration, spray angle and breakup of high density droplets region in the spray were affected with injection pressure. The results and techniques of spray visualization and injection rate measurement in this study would be practically effective to study a high pressure diesel spray for common rail direct injection system.

• 한국세라믹학회지
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• 제32권9호
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• pp.1047-1055
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• 1995

Mn-Zn ferrite granules were formed by a spray-drying method of the slurry containing different kinds and concentrations of binders at various temperatures. The slurry was made by conventional ceramic processing method, that is, by mixing Fe2O3, MnO, ZnO powders (52 : 24 : 24 mol%), calcining and milling. Typical shape of the spray dried granules was spherical. The compaction behavior of these granules was dependent on the spray-drying temperature and the kind and concentration of binders. At lower pressure the granules were displaced and at higher pressure the granules were deformed and fractured to fill pores among the granules. The optimum concentration of the binder was 0.5wt%. The granules containing 0.5wt% PVA 205 were deformed and fractured well and the green density was higher than others. At higher concentrations of the binder the granules were deformed rather than fractured, therefore the green density was lowered because of the remaining unfilled pores. The decomposition temperature and the heat released were increased with increasing the concentration of the binders. The compaction response of the granules containing PVA 205 was more efficient than those containing PVA 217 and PVA 117. Green density was not dependent on the degree of hydrolysis of the binders. The compaction response of the granules spray-dried at 15$0^{\circ}C$ was most efficient.

• 한국분무공학회지
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• 제18권3호
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• pp.140-145
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• 2013

Sub/supercritical spray experiments were conducted, and cryogenic nitrogen and gaseous argon were selected for simulants. liquid nitrogen and gaseous argon were injected in subcritical case, and supercritical nitrogen and near-critical gaseous argon were injected in near-critical/supercritical cases. shadowgraph method was used to visualize spray, and analyzed about the breakup length. The breakup length was measured from numbers of Instantaneous shadowgraph Images from each case, and they were compared with momentum flux ratios and density ratios. It was observed that the relation between breakup length and momentum flux ratio was fitted into former experiment results. and the reasonable constant was suggested about the relation between breakup length and density ratio.

• 한국항공우주학회지
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• 제34권7호
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• pp.97-104
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• 2006

분사조건과 주위기체 압력에 따라 스월 인젝터의 분무각과 분열길이를 측정함으로써, 스월 인젝터의 분무 및 분열특성에 대한 연구를 수행하였다. 분사조건으로 축방향 We 수(Wel)를 1554까지 주위기체 압력을 4.0MPa까지 증가시켰다. Wel과 주위기체 밀도(ρ)가 증가함에 따라 공기역학적 힘이 증가하여 원추형 액막 표면의 교란이 증가하게 되고, 따라서 분열이 빨리 일어난다. 결과에 따르면 주위기체 밀도에 따른 분무각의 변화가 분열이 일어나기 전과 후가 다르게 나타났다. 분열이전에는 분무각이 주위기체 밀도 변화에 관계없이 거의 일정하였으나, 분열이 일어나게 되면 분무각이 감소하게 된다. 또한 측정된 분열길이를 선형불안정이론과 비교해 보았는데, 액막두께의 감쇠를 고려한 수정된 이론이 측정결과와 상당히 유사한 결과를 얻을 수 있었다.

• 대한기계학회논문집B
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• 제27권4호
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• pp.484-495
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• 2003

This study investigates the flow characteristics of fuel droplets between twin spray for the 4-hole injector used a 4-valve gasoline engine. The injectors for this study were the three types of 4-hole gasoline injector in which orifice diameter was 0.24mm. The spray behavior of twin spray was investigated by means of visualization employed stroboscope. A PDPA system was employed to simultaneously measure the size and velocity of fuel droplets. The 3 dimensional mean velocities. droplet size distributions, SMD and joint probability density function of velocity and droplet size are analyzed at the center of the spray and the center region of twin spray. As a result, the configurations of injector exit such as orifice interval and length of outlet, are very important factors that affect the flow characteristics of fuel droplets at the center region of twin spray.

• 한국분무공학회지
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• 제16권2호
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• pp.90-96
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• 2011

Atomized liquid jets from the washing nozzle which configured with recirculation chamber for cleaning hot-zone area are accelerated and impinged on the head lamp surface. Cleaning efficiency of head lamp can be increased with injecting washing fluids into the hot-zone area. Experimental and numerical studies with various design parameters were executed to reveal the relations between internal geometry and internal flow in the washing nozzle. Spray structures were fitted with each of the head lamp surfaces and spray nozzles were optimized to the spray pattern. The recirculation chamber induces a recirculation flow and can be decreased the pressures perturbation inside the chamber. Orifice determines the mass flow rate. When the diameter of orifice is excessively large, it showed an unstable spray pattern. As a nozzle exit angle increases, density distributions are separated with two section. Also, as a protrusion length of nozzle exit increases, spray patterns are spread into a large area and density distributions showed unstable trend.