• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.1
• /
• pp.87-100
• /
• 1997

The ability of turbulence model to accurately describe the complex characteristics of the flow field and the fuel spray is of great importance in the optimum design of diesel engine. The numerical simulations of the flow field and the spray characteristics within the combustion chamber of direct injection model entgine are performed to examine the applicability of turbulence model. The turbulence models used are the RNG $\varepsilon$ model and the modified $\varepsilon$ model which included the compressibility effect due to the compression/expansion of the charges. In this study, the predicted results in the quiescent condition of direct injection model engine show reasonable trends comparing with the experimental data of spray characteristics, i. e., spray tip penetration, spray tip velocity. The results of eddy viscosity obtained using the $\varepsilon$ model in the spray region is significantly larger than that obtained using the RNG $\varepsilon$ model. The application of the RNG model seems to have some potential for the simulations of the spray characteristics, e. g., spray tip penetration, spray tip velocity, droplets distribution over the $\varepsilon$ model.

• Journal of ILASS-Korea
• /
• v.20 no.4
• /
• pp.261-267
• /
• 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.

• Journal of ILASS-Korea
• /
• v.22 no.2
• /
• pp.80-86
• /
• 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.

• Journal of ILASS-Korea
• /
• v.26 no.2
• /
• pp.88-95
• /
• 2021

This study aims to investigate the influence of the droplet volume on the evaporation characteristics of the sessile droplet. In particular, the effect of the free convection in the vapor domain on the evaporation rate was analyzed through the numerical simulation. The commercial code of the ANSYS Fluent (V.2020 R2) was used to simulate the heat transfer in the liquid-vapor domain. Moreover, we used the diffusion model to estimate the evaporation rate for the different droplet volume under the room temperature. It was found that the evaporation rate significantly increases with the droplet volume because of the larger surface area for the mass transfer. Also, the effect of free convection on the evaporation rate becomes significant with an increment of droplet volume owing to the increase in the droplet radius corresponding to the characteristic length of the free convection.

• Korean Journal of Food Science and Technology
• /
• v.38 no.1
• /
• pp.52-58
• /
• 2006

Characteristics of dough added with up to 4.0% takju powder and resultant bread were studied. Doughs added with takju power spray-dried after fermentation with starter (SDWS) and takju power spray-dried after fermentation without starter (SDOS) showed higher pH decreases than those added with takju power freeze-dried after fermentation with starter (FDWS) and takju power freeze-dried after fermentation without starter (FDOS) even after 1st fermentation. After 1st fermentation, volume of dough added with 1-4% SDWS was high, with 1% SDWS showing highest value of 23.6 mL. Volume of bread added with SDOS showed highest value. At 1-2% SDWS and SDOS addition, doughs showed highest specific volume values, which decreased at higher than 3% addition, while specific volume increased with increasing FDWS and FDOW contents. L values of SDOS- and FDOS-added doughs decreased gradually with increasing SDOS and FDOS contents compared to SDWS and FDWS addition. In loaf bread added with takju powder less than 2%, loaf bread added with spray-dried takju powder had higher appearance, color, texture, taste, and overall acceptability values compared to those added with freeze-dried takju. Although not significantly, loaf bread added with 1% SDWS showed slightly higher values in appearance, color, yeastiness, texture, taste, and overall acceptability, and showed higher flour odor acceptability than non-added loaf bread. These results indicate addition of takju powder improves flavor of bread.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.9
• /
• pp.909-916
• /
• 2015

In this study, to investigate the effect of spray behavior characteristics, we induce the mixing ratio of emulsified fuel using impinging spray. We formulate the emulsified fuel by mixing diesel and hydrogen peroxide($H_2O_2$). We set the temperature of the heating plate to $150^{\circ}C$, $200^{\circ}C$, and $250^{\circ}C$, and set the injection pressures to 400, 600, 800, and 1000bar. The surfactants for the emulsified fuel mixture, which were mixed span80 and tween80 was mixed as 9:1, were fixed to 3% of the total volume of the emulsified fuel. We set the mixing ratio of $H_2O_2$ in the emulsified fuel as emulsified fuel(EF)0, EF2, EF12, and EF22. Further, we visualize the evaporation impinging spray using the Schlieren method. Based on the results of this study, we found that a higher temperature and injection pressure of the heating plate impingement led to the active diffusion of the fuel vapor, which promoted emulsified fuel evaporation. When the emulsified fuel is utilized in an actual engine, because of the temperature-drop effect of the combustion chamber, which is due to the evaporation of $H_2O_2$ in fuel and faster mixture formation is expected to decrease the engine emissions.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.1
• /
• pp.345-350
• /
• 2017

Downsizing is widely applied to diesel engines in order to improve fuel efficiency and reduce exhaust emissions. Engine sizes are becoming smaller but pressure and temperature inside combustion chambers are increasing. Therefore, research for fuel spray under high pressure and temperature conditions is important. A constant volume chamber which simulates high temperature and pressure likely to be found in diesel engines was developed in this study. Pressure and temperature were increased abruptly because of ignition of the pre-mixture in the constant volume chamber. Then pressure and temperature were gradually decreased due to the heat loss through the chamber wall. Fuel spray occurred when temperature and pressure were reached at the target condition. In this experiment, the temperature condition should be exactly defined to understand the relation between fuel evaporation and ambient temperature. A fast response thermocouple was developed and used to measure the temporal and spatial temperature distribution during the combustion process inside the combustion chamber. In the results, the core temperature was slightly higher than the bulk temperature calculated by the gas equation. Ed-note: do you want to say 'ideal gas equation'? This was attributed to the heat transfer loss through the chamber wall. The vertical temperature deviation was higher than the horizontal temperature deviation by 5% which resulted from the buoyancy effect.

• Proceedings of the Korean Society of Postharvest Science and Technology of Agricultural Products Conference
• /
• 2003.04a
• /
• pp.135-136
• /
• 2003

알코올 분무, 셀로판지 부착 등의 표면처리가 포장김치의 표면갈변과, pH, 산도, 균수 및 관능적 품질에 미치는 영향을 조사하였다. 실험에 사용된 포장김치는 200 g 들이 플라스틱 용기에 김치를 담은 후 무처리, 70% 알코올로 표면을 1회 분무한 것, 김치표면에 폴리에틸렌필름(두께 0.04 mm)을 부착하여 저장실 (10$\pm$1$^{\circ}C$)에서 21일간 저장하면서 3일 간격으로 조사하였다. 그 결과, 무처리와 알코올을 분무한 경우는 저장 15일째에 pH가 4.0수준에 도달하였으나 김치표면에 polyethylene film을 부착한 경우는 21일째까지도 pH가 4.0 이상을 유지하였다. 산도의 경우도 pH와 동일한 경향을 나타내어 polyethylene film으로 표면처리함으로서 김치의 숙성이 지연되었다. 무처리와 알코올을 처리한 것은 12일째부터 김치표면이 갈변하기 시작하였으며 18일째는 그 갈변정도가 심하였다. 그러나 polyethylene film을 표면에 부착한 경우는 저장 21일째까지도 갈변정토가 미약하였다. 저장기간에 따른 총균수의 변화는 무처리와 알코올을 처리한 경우가 polyethylene film을 부착한 경우에 비하여 증가폭이 컸으나 젖산균수는 반대로 polyethylene film을 부착한 경우가 무처리 또는 알코올을 분무한 경우에 비하여 높아 김치의 품질이 양호하였다. 무처리와 알코올을 분무한 김치의 표면에는 저장 15일 이후에 산막표모 및 곰팡이의 균사체가 번식하는 김치도 발견되었다. 처리별 이미 및 이취의 발생정도를 조사한 결과 무처리와 알코올을 처리한 경우는 저장 15일경에 특히 용기 표면에 위치하는 김치에서 이미와 이취가 있었으나 polyethylene film을 부착한 경우는 이미와 이취가 전혀 나타나지 않았다.채반에 넣고 밀도를 측정한 결과 1.002g/㎤을 나타냈다. 즉 물의 이론밀도인 1g/㎤에 근접한 값을 보여 정확한 밀도 계측이 가능한 것으로 판단되었다. 또한 밀도 계측시스템의 측정 반복간 정밀도를 파악하기 위해 수박 6개를 임으로 선정하여 3반복 측정 시험한 결과, 측정표준편차가 0.001~0.004g/㎤로 해상도보다는 다소 높았으나 대체로 양호한 결과를 나타냈다. 수박 35개를 이용하여 개발 계측시스템과 사람이 직접 부력법으로 밀도를 측정 비교한 결과, 계측시스템에 의해 측정된 수박 밀도가 사람이 측정했을 때 보다 낮게 측정되었다. 수박의 외관인자(무게, 길이, 직경, 체적), 밀도와 당도의 상관관계 구명시험을 위해 원예연구소 시험포장에서 재배된 삼복꿀수박 총 74개를 공시재료로 하였고, 시험은 출수일별로 10~14개씩 수확하여 외관인자, 밀도, 당도를 각각 측정하고, 이들 인자들간의 상관관계를 구명하였다. 외관인자들간에는 높은 상관관계를 보였으나, 외관인자들과 밀도, 외관인자들과 당도, 밀도와 당도와는 매우 낮은 상관관계를 나타냈다. 점성에 영향을 미치는 가장 주요한 조건이라고 생각된다.환원당인 sucrose 함량은 계속 증가하였고 fructose, glucose, sorbitol의 함량(추황의 sorbitol을 제외)은 생장이 촉진됨에 따라 증가하다가 다시 점차적으로 감소하였다. 이러한 결과는 총당과 환원당의 측정결과와 일치한 것으로 나타났다. 결론적으로 배의 성장에 따라 산 함량은 감소하였고 당 함량은 증가하였다.luco-pyranoside, quercetin 7-O- -glucopyranoside, acacetin 7-O-$\beta$-D-glucuronide and apigenin-6-C-$\beta$-D-glucopyranosyl-8-C-$\b

• 한국연소학회:학술대회논문집
• /
• 2002.11a
• /
• pp.141-148
• /
• 2002

Experimental investigation of the interaction between dual spray formed by swirl type injector was conducted. Experimental parameter was fuel temperature, varied in the range from $-20^{\circ}C$ to $120^{\circ}C$. Measuring parameter were vertical distance from injector tip to patternator and gap between injectors. Volumetric distiribution and SMD were measured for the various combination of parameters. The results of present study show that the arithmetic sum of each of spray is not equal to dual spray, but it is equal above specific fuel temperature. As the increases of fuel temperature, SMD decreases and becomes more uniform. As the increases of gap between injectors, fuel volume and SMD at collision area increases, but penetrated fuel decreases.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.4
• /
• pp.521-531
• /
• 1996

Inorganic and inorganic/organic microcapsules were prepared by spray drying. $K_{4}SO$ and clay were used as the core and colloidal silica as the shell for the inoroganic microcapsules. Forthe inorganic/organic microcapsules were used the inorganic microcapsule which were mentioned above (core) and ethyl cellulose (shell). To characterize the prepared microcapsule for the practical use, the homogenity of surface and pore volume are the dominent factors. At the volume ratio of 0.3/0.7 of core/shell, the spherical and homogeneous surfaces of inorganic microcapsule could be synthesized. In the case of inorganic/organic microcapsules, the weitht ratio was 0.76/0.24. The pore volume of inorganic/organic microcapsules decreases more than that of inorganic microcapsule. The more the amount of shell (ethyl cellulose) in inorganic/organic microcapsules increases, the more the coating became homogeneous and the pore volume decreased.