• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 2008년도 추계학술논문발표회 논문집
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• pp.363-370
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• 2008

The present study has been performed to investigate the effect of statistical number of droplets on the simulation of the sprinkler spray using fire field model. In order to simulate the sprinkler spray characteristics, the present study uses NIST Fire Dynamics Simulator version 5.2. A group of Lagrangian particle with similar droplet characteristics, such as diameter, velocity, temperature and so on, is represented by parcel concept to decrease the total number of droplets tracked in the simulation. The present study introduces a new parameter to represent the ratio between real number of droplets and computational parcels. The dependency of the number of parcels on the fire suppression characteristics and spray patterns is quantitatively examined for different ratio between the real number of droplets and computational parcels.

• 한국전산유체공학회지
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• 제2권2호
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• pp.89-96
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• 1997

High injection pressure system has been developed as a measure to reduce harmful exhaust gases. In order to understand the effect of pressure on diesel spray injection process, wide range of high injection pressure was tested. The gas phase is modelled by the Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled following the discrete droplet model approach in Lagrangian form. The droplet distributions, vapor fractions and gas flows are analyzed in various injection pressure cases. The distributions of spray and vapor increase and the Sauter mean diameter decreases with increasing injection pressure quickly in a low pressure area but slowly in a high pressure area.

• Journal of Mechanical Science and Technology
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• 제14권12호
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• pp.1376-1385
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• 2000

This study investigates spray characteristics before and after wall impingingment of gasoline spray in suction air flow. For this study, a rectangular model intake port was made of acrylic glass, and suction air was generated by using the forced air blower contrariwise. The injector for this study was a pintle-type port gasoline injector in which an air-assist adaptor is installed to supply assisted air. A PDPA system was employed to simultaneously measure the size and velocity of droplets near the wall. Measured droplets are divided into "pre-impinging droplets"with positive normal velocity and "post-impinging droplets"were negative normal velocity for the suction flow. The velocities, size distributions and Sauter mean diameter(SMD) of pre-and post-impinging droplets for varions injection angles and air-assists are comparatively analyzed.

• Journal of Advanced Marine Engineering and Technology
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• 제23권1호
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• pp.47-53
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• 1999

Small compression-ignition direct injection engines have been developed as a measure to improve a fuel efficiency and reduce harmful exhaust gases. Those small engines generally employ high injection pressure increase on the spray impacting on a wall is discussed in this paper. The gas phase is modelled by the Eulerian continuum conservation equations of mass momentum energy and fuel vapour fraction. The liquid phases is modelled following the discrete droplet model approach in Lagrangian form and the droplet wall interaction is modelled as a func-tion of the velocity normal to impaction lands. The droplet distributions vapor fractions and gas flows are analyzed in various injection pres-sure cases. The penetrations of wall spray and vapor increase and the Sauter mean diameter decreases with increasing injection pressure.

• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 2008년도 춘계학술논문발표회 논문집
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• pp.200-203
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• 2008

Water mist fire suppression system utilizes the fire suppression features such as cooling of fire source, dilution of ambient oxygen, and shielding of radiation heat with the evaporation of microscopic water droplets. The momentum of water mist is relatively low and the infiltration of water mist to the fire source is not effective. In addition to lower penetration force, the evaporated water vapor is liable to decline to limited portion of fire source due to its light weight and sparse density. On the other hand, the cycling water mist system is expected to improve the penetration force of water mist as well as the dilution coverage capability with the stratified spray characteristics. At this paper we present the analyzed fire suppression capability of intermittent water spray pattern by use of FDS which is computational fire dynamics fire model. We expect this analysis shall be supportive to the development of the prototype of water mist nozzle.

• 한국분무공학회지
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• 제4권3호
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• pp.15-23
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• 1999

The use of LPG as clean fuel for Diesel engine is very attractive way to reduce soot and NOx emission. In this study, a numerical study has been done to know the transient behavior of LPG fuel in chamber pressures which is held at a pressure above (0.37MPa)and below(0.15MPa)the fuel vapor pressure. Results show that the vortex formed within the start of injection at the leading edge of the spray cone and was most apparent for 0.15MPa chamber pressure case. The high speed photographs and model results showed a narrower cone angle during the quasi-steady spray period at the 0.37MPa chamber pressure compared to the 0.15MPa case. And it can be shown that more realistic vaporization process is necessary to predict the spray length well.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3085-3089
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• 2008

In order to reduce NOx and Soot emissions simultaneously, characteristics of diesel spray and combustion were investigated by numerical simulation with StarCD in this paper. This work focuses on effect of Spin Injection. A simulation model of combustion, spray and emissions is developed for heavy duty marine diesel engine application. Simulation is performed with change of spray angle between first and second directions at fixed engine speed, injection timing, injection duration and etc. The results show that Spin Spray Injection method can reduce NOx emission. And the results show that the 1st injection considerably interfere with 2nd injection characteristics.

• 한국화재소방학회논문지
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• 제30권6호
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• pp.111-117
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• 2016

본 연구는 스프링클러 헤드 근처에서 형성되는 액막의 자유표면 유동에 대해 CFD 모델을 적용하여 해석하고 스프링클러의 초기분무 특성 예측을 위한 기존 이론식의 결과와 비교를 통해 이론 모델의 타당성을 검토하였다. CFD 해석은 상용 해석프로그램인 CFX 14.0을 이용하였으며 노즐과 디플렉터로 이루어진 단순형상에 대해 표준난류모델과 VOF법을 적용하여 해석을 수행하였다. 평판부의 디플렉터 끝단에서 속도분포는 CFD 해석과 경험식이 매우 잘 일치된 결과를 보였으나 기하학적 형상이 복잡한 부분에서는 속도분포의 차이를 보였다. 이론모델에서 예측된 평균액적크기는 실제 스프링클러 헤드에서 측정된 평균액적크기에 대한 이전 연구결과와 큰 차이를 보였다. 그러나 이론 모델은 스프링클러 헤드의 초기 액적형성과정의 메커니즘을 이해하고 실험적 접근이 용이하지 않은 상황에서 분무 액적의 특성을 예측하는데 유동한 도구로 활용될 수 있다.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.87-95
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• 2002

The aim of this article is to perform the numerical simulation far drop drag and breakup processes in air-assisted sprays using the Taylor analogy breakup (TAB) model with a modified drop drag model, in which a random method is newly used to consider the variation of the drop's frontal area. The predicted results for drop trajectory and Salter mean diameter (SMD) were compared with experimental data and the simulation results using the earlier published models such as TAH model, surface wave instability (Wave) model, and Wave model with original drop drag model. In addition, the effects of the breakup model constant, Ck, on prediction of spray behaviors were discussed. The results shows that the TAB model with the modified drop drag model is in better agreement with experimental data than the other models, indicating the present model is acceptable for predicting the drop breakup process in air-assisted sprays. At higher Weber numbers, the smaller Ck shows the best fitting to experimental data. It should be noted that more elaborated studies is required in order to determine the breakup model constant in the suggested model in the study.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.381-386
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• 2007

액체 연료를 사용하는 가스터빈 연소기에서의 분무 및 연소 특성을 알아보기 위해 본 연구에서는 KIVA-3V를 이용하여 애뉼러형 모형 가스터빈 연소기에서 Jet-A의 분무와 연소에 의한 열유동 현상을 수치해석을 통하여 연구하였다. 홀을 통해 유입되는 냉각유동이 있을 경우, 유입 유동이 최적화되지 않으면 액체연료의 분무는 주위 유동장의 영향을 크게 받아 후류에서 SMD가 증가하고, 등가비의 수직적 분포가 일어나기 어렵게 된다. 화염이 연소실의 중앙 부분에서 좌우로 넓게 발생하며, 유동에 의해 화염의 후류가 갈라지는 현상이 있었으며 이로 인해 화염중심부가 분리되고 국소적인 고온부가 생성되어 NO의 발생이 증가하는 영역이 발생하였다.