• 한국자동차공학회논문집
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• 제14권4호
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• pp.132-138
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• 2006

Numerical analysis about atomization and wall impingement process of hollow-cone fuel spray is performed by a modified KIVA code with hybrid model. The atomization process is modeled by using hybrid breakup model that is composed of Linearized Instability Sheet Atomization(LISA) model and Aerodynamically Progressed Taylor Analogy Breakup(APTAB) model. The Gosman model, which is based on the droplet behaviors after impingement determined by experimental correlations, is used for spray-wall impingement process. The LIEF technique was used to compare the results with those of experiment. The calculations and experiments are carried out at the ambient pressures of 0.1 MPa and 0.5 MPa and the ambient temperature of 293K. It was found that the calculated results show satisfactory agreement with experimental ones.

• 한국분무공학회지
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• 제24권4호
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• pp.185-193
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• 2019

The effervescent atomizer is one of twin-fluid atomizers that aeration gas enters into bulk liquid and two-phase flow is formed in the mixing section. The effervescent atomizer requires low injection pressure and small amount of aeration gas, as compared to other twin-fluid atomizers. In this study, cold flow test was conducted to investigate the spray characteristics of aerated impinging jets. The present effervescent impinging atomizers were composed of the aerator device and like-on-like doublet impinging atomizer which had different impinging angles. To analyze the spray characteristics such as breakup length and droplet size distribution, the image processing technique was adopted by using instantaneous images at each flow condition. Non-dimensional parameters, induced by the homogeneous flow model, were used to predict the breakup length. The breakup length was decreased with the mixture Reynolds number and impinging angle increasing. The result of droplets showed that the size distribution was axisymmetric about the center of the injector and their diameter tended to decrease with increasing GLR.

• 대한기계학회논문집B
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• 제31권12호
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• pp.971-978
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• 2007

A spray-wall impingement process of a hollow-cone fuel spray from the high-pressure swirl injector in the Gasoline Direct Injection (GDI) engine were experimented and calculated at various wall geometries. The Linearized Instability Sheet Atomization (LISA) & the Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model and the Gosman model were applied to model the breakup and the wall impingement process of the hollow-cone fuel spray. The numerical modelings were implemented in the modified KIVA code. The calculation results of spray characteristics, such as a spray development process and a radial distance after wall impingement, compared with the experimental results by the Laser Induced Exciplex Fluorescence (LIEF) technique. The droplet size distribution and the ambient gas velocity field, which are generally difficult to obtain by the experimental methods, were also calculated and discussed. It was found that the radial distance after wall impingement and Sauter Mean Diameter (SMD) decreased with increasing a cavity angle.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.156-160
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• 2006

본 연구에서는 액체 추진제 로켓엔진의 연소기에 주로 사용되는 액체-액체 동축 스월형 분사기의 분무특성에 대해 고찰하였다. 액막의 분열에는 선형 안정성 이론[1]을 도입하였고 분열 후 충돌에는 충돌이후 분열이 고려된 Post[2]의 모델을 사용하였으며, solver로는 KIVA[3]를 사용하였다. 이러한 모델을 통해 디젤 엔진에 적합한 고속 분사와 로켓엔진에 적합한 저속 분사를 각각 검증하였고 실험결과와 잘 일치하는 것을 볼 수 있었다.

• Nuclear Engineering and Technology
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• 제22권4호
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• pp.326-336
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• 1990

최근 수행된 일련의 실험들을 통하여 핵연료 집합체 지지격자(Spacer Grid)의 존재가 냉각재상실사고시에 핵연료봉으로부터의 열제거에 긍정적인 효과를 미치고 있음이 밟혀졌다. 그 이유는 열원이 없는 지지격자가 연료봉보다 먼저 ？칭이 일어나며 물방울이 지지격자에 부딪쳐서 잘게 부수어져 증발이 쉽게 일어나게 되고 또한 난류효과를 증대시키는 요인이 되기 때문이다. 따라서 냉각재상실사고의 진행 과정에서 첨두피복관온도가 발생하는 재관수 구간의 수면 위쪽에서 유지되는 DFFB에서의 정확한 열전달을 계산하기 위해서는 이들의 고려가 필요하다. 본 논문에서는 DFFB에서 지지격자의 존재로 인해 물방울이 잘게 부수어져 증발이 쉽게 이루어지도록 하는 Droplet Breakup Model을 냉각재상실사고 최적해석 코드인 RELAP5/MOD2에 삽입하였다. 재관수 구간에서 지지격자의 영향을 체계적으로 조사한 FEBA실험에 대해서 검증계산을 수행하여 실험자료와 비교하였다.

• 설비공학논문집
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• 제18권4호
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• pp.344-350
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• 2006

The present study investigates the characteristics of fire-driven heat flows and gas concentration in a compartment fire by using the modified VHS model (MVHS). The main idea of this model is to add some source terms for combustion products and oxygen consumption to the original VHS model for providing more accurate and useful information on gas concentration distributions as well as thermal fields. It is found that the present MVHS model shows fairly good agreement with the experimental data and the eddy breakup combustion model. The tilting angle of fire plume calculated by MVHS is larger than that of EBU model because the fire source of VHS is affected by ventilating flow less than EBU. However, this discrepancy is apparently reduced in the downstream region of fire source.

• 대한기계학회논문집B
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• 제28권5호
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• pp.545-552
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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. Several models have been introduced and compared. The atomization process was modeled using hybrid breakup model that is composed of Linearized Instability Sheet Atomization (LISA) model and Aerodynamically Progressed TAB (APTAB) model. The vaporization process was modeled using Spalding model and Abramzon ＆ Sirignano model. Exciplex fluorescence method was used for comparing calculated with experimental results. The experiment and computation were performed at the ambient pressure of 0.1 MPa, 0.5 MPa and 1.0 MPa and the ambient temperature of 293k and 473k. Comparison of calculated and experimental spray characteristics was carried out and the calculated results of GDI spray showed good agreement with experimental results.

• 한국분무공학회지
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• 제10권4호
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• pp.47-53
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• 2005

This paper presents the effects of ambient pressure on atomization characteristics of high-Pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a shadowgraph technique. In order to investigate the atomization process numerically, the LISA-DDB hybrid model was utilized. This breakup model assumes that the primary breakup occurs when the amplitude of the unstable waves is equal to the radius of the ligament of liquid sheet near the nozzle and the droplet deformation induces the secondary breakup. The results provide the effect of ambient pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is also revealed that the accuracy of prediction of LISA-DDB hybrid model is pretty good in terms of spray developing process, spray tip penetration, and SMD distribution.

• 동력기계공학회지
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• 제21권4호
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• pp.34-41
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• 2017

Diesel engines with compression-ignition type have superior thermal efficiency, durability and reliability compared to gasoline engine. To control emitted gas from the engines, it can be applied to alternative fuel without any modification to the engine. Therefore, in this study, as a basic study for applying emulsified fuel to the actual diesel engine, analysis of spray behavior characteristics of emulsified fuel was carried out simultaneously by experimental and numerical method. The emulsified fuel consist of diesel, hydrogen peroxide, and surfactant. The surfactant for manufacturing emulsified fuel is comprised of span 80 and tween 80 mixed as 9:1 and fixed with 3% of the total volume of the emulsified fuel. In addition, six kinds of emulsified fuel(EF0, EF2, EF12, EF22, EF32, and EF42) were manufactured according to the mixing ratio of hydrogen peroxide. The droplet and spray experiments were performed to observe the behavior characteristics of the emulsified fuel. The numerical analysis was carried out using ANSYS CFX to confirm the microscopic behavior characteristics. Consequently, rapid mixture formation can be expected due to evaporation of hydrogen peroxide in emulsified fuel, and it is confirmed that Reitz&Diwakar breakup model is most suitable as breakup model to be applied to the numerical analysis.

• 한국항공우주학회지
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• 제44권4호
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• pp.290-297
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• 2016

사각덕트에서 난류 유동장으로 분사되는 액체 제트의 액주 분열과 미립화 현상에 관한 LES를 수행하였다. 기체상태의 공기 유동 해석에 오일러리안 해법을 사용하고, 액적 추적을 위하여 라그랑지안 해법을 사용하여 기체-액체간 이상유동(two phase flow) 해석을 수행하였다. 액적 분열 모델, 아격자 스케일 모델 및 공간 차분법에 따른 액적 분열을 조사하였다. 액체 제트의 침투깊이를 경험식과 비교하였으며 경험식보다 약간 높음을 알 수 있었다. 제트 후류에서 사우터 평균직경에 대한 분석을 수행하였다.