• Journal of the KSME
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• v.23 no.4
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• pp.288-294
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• 1983

고속기류에 의한 수표면의 유통은 호수나 강에서 흔히 볼 수 있는 물리적인 현상으로서 기류의 속도가 증가함에 따라서 수표면에서 액적이 발생하게 되는 이른바 액체미립화 현상(atomization )이 일어나게 된다. 이러한 액체의 미립화는 내연기관에서의 분무연소에서 부터 가정에서 습도를 유지하는 가습기 및 살충제분무기에 이르기까지 그 운용도가 매우 광범위하며 최근에 이르러 액체미립화가 유체역학의 한 부분을 차지하는 단계에까지 이르러 매년 각국에서 미립화에 대한 심포지움이 개최되고 있으며 연구실적면에서는 미국보다도 오히려 가까운 일본에서 미립화에 대한 연구가 더 활발히 진행되고 있는 반면 아직 우리나라에서는 이렇다할 연구가 없으며 미립 화에 관한 논문도 불과 한두 편에 이르는 실정이다. 이러한 중요한 물리적인 현상에 대해 좀더 자세한 이해를 위해서는 액체와 기체의 상호접촉면에서의 정량적인 특성에 대한 연구가 필요하며 이러한 정량적 인자에는 (1) 액막의 평균두께 (2) 액막내의 속도분포, (3) 액막표면의 파고, 파장의 파면구조, (4)기체중의 속도분포 등이 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.3021-3031
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• 1994

Experiments have been performed to find out the effect of the mixing port length of Y-jet atomizers on the spray performance, using air and water as the test fluids. Water and air flow rates and drop sizes were measured at each injection pressure condition for different mixing port length. The air flow rate was almost unaffected by the change of the mixing port length. However, the water flow rate was relatively susceptible to the change of the mixing port length. The mixing point pressure was very much influenced by the mixing port length. Variations of spatial distribution of Sauter Mean Diameter (SMD, $D_{32}$) and the cross-section-averaged SMD ($D_{32,m}$) with different mixing port length and air/water mass flow rate ratio were examined. Generally, when the mixing port length was reduced, the mean drop size decreased and became spatially even.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.659-669
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• 1997

The effects of exhaust gas recirculation on diesel engine combustion and soot/NOx emissions are numerically studied. The primary and secondary atomization is modelled using the wave instability breakup model. Autoignition of a diesel spray is modelled using the Shell ignition model. Soot formation is kinetically controlled and soot oxidation is represented by a model which account for surface chemistry. The NOx formation is based on the extended Zeldovich NOx model. Effects of injection timing and concentration of $O_{2}$ and CO$_{2}$ on the pollutant formation and the combustion process are discussed in detail.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.16-16
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• 1998

로켓의 추진제에는 고체 추진제와 액체 추진제를 사용하는 두 경우로 나눌 수 있는데, 액체 추진제를 사용하는 경우, 액체 연료와 액체 산화제를 다양한 방법으로 연소실내로 분사하게 된다. 이때 사용되는 injector들 중에 impingement type이 있다. 이 type은 injector의 가공이 비교적 용이하고, 혼합성능이 좋기 때문에 LOX/RP-1(Kerosin-based hydrocarbon fuel)을 사용하는 액체 로켓엔진에서 주로 사용되어 왔다. 두 액체 jet의 충돌에 의해 액막이 형성되는데, 이 액막은 가장자리로 갈수록 두께가 얇아지며 액막표면의 파는 충돌점으로부터 멀어질수록 그 진폭의 증가를 이루어 액체의 표면장력과 관성력의 균형을 깨트리며, 이 순간 액막은 rim의 형태로 분열하여 결국에는 액적을 생성하게 된다. 현재까지의 연구내용은 충돌 jet의 형태 laminar jet과 turbulent jet으로 구분된 인젝트에 관해 연구되어왔고, 특히 국내에는 이러한 구분된 충돌 jet의 분열현상에 관한 연구결과가 미흡하다. 동일한 오르피스의 경우에도 laminar jet과 turbulent jet으로 구분되어 지며, 각각의 jet의 형태에 따라 생성되는 액막의 형상 또는 다르게 생성되어 진다. 그러므로 본 연구에서는 두 구분된 jet의 경우의 분열현상을 실험적으로 분석하였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.94-103
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• 1999

A model for the prediction of combustion and exhaust emissions of DI diesel engine has been formulated and developed . This model is a quasi-dimensional phenomenological one and is based on multi-zone combustion modelling concept. It takes into consideration, on a zonal basis ,detailed of fuel spray formation, droplet evaporation, air-fuel mixing, spray wall interaction, swirl , heat transfer, self ignition and burning rate . The emission model is considered with chemical equipment , as well as the kinetics of fuel. NO and soot reactions in order to calculate the pollutant concentrations within each zone and the whole of cylinder . The accuracy of prediction versus experimental data and the capability of the model in predicting engine heat release, cylinder pressure and all the major exhaust emissions on zonal and cumulative basis., is demonstrated. Detailed prediction results showing the sensitivity of the model bv various injection rates are presented and discussed.

• Journal of the Korean Applied Science and Technology
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• v.31 no.3
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• pp.492-499
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• 2014

The objectives of this study was to examine experimentally the microexplosion phenomena of single droplet W/O(water-in-oil) type emulsified fuel. Also, measured the combustion characteristics of single droplet emulsified fuel for microexplosion phenomena in atmospheric pressure condition. The larger quantity of adding water makes microexplosion phenomenon with higher intensity of sound level, because larger water droplet has better coalescence for emulsified fuel. The small quantity of adding water makes puffing with lower sound level intensity. In latter period of extinction, large size droplet of the emulsified fuel breaks down rapidly to small size droplet, and microexplosion phenomenon occurs with multi step combustion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.799-804
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• 2007

The behavior of spray emanating from an injector to be employed in a liquid-propellant thrust chamber is investigated by optical measurement techniques. The injector has eight holes, each of which has 30 cant angle from the center-axis with the diameter of 0.406 mm. In order to examine an atomization process according to the spray-generation conditions and the evolution along spray downstream, variational features in the velocity and size of droplets obtained through Dual-mode Phase Doppler An 799emometry (DPDA) are delineated and discussed together with instantaneous plane images captured by using Nd:Yag laser sheet beam. A categorization of spray-flow regime representing the atomization and turbulent nature is made through evaluating the non-dimensional parameters, i.e., Reynolds number and Weber number based upon the theoretical injection velocity. These qualitative and quantitative data of spray breakup will be a firm basis for the design of brand-new thruster

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.402-410
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• 2000

As the combustion process of CWM consists of the water evaporation, the release and combustion of volatile matter, and the combustion of char for every particle, it is more complex than that of existent liquid fuel. Though the many studies on CWM combustion have been carried out by the single droplet using hanging methods or the multiple droplet using atomization methods, any report don't presents definite solution about the effects by the initial water evaporation and combustion of volatile. When CWM is suddenly exposed in the high temperature surroundings, the internal water evaporates and then each droplet builds up pores. Besides, porosity rate changes along the temperature of surroundings, the composition ratio of CWM, and the initial diameter of droplet. In result, because it affects the whole combustion rate, the combustion of CWM has complex mechanism as compared with the combustion of liquid or gas fuel. Therefore, concentrating on porous structure of CWM, this study has proceeded to acquire the basic data on the CWM injection combustion and closely examines the effects of the first stage combustion on the whole combustion by measuring the diameter variations, pore rate, mass fraction burned, and the internal temperature changes of CWM droplet. The results demonstrate that $60{\sim}70%$ of initial mass is reduced during water evaporation and volatile combustion period, and swelling rate, mass faction burned, and density variation are greatly concerned with atomization of CWM etc.

• Journal of ILASS-Korea
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• v.8 no.3
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• pp.41-48
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• 2003

This work was performed to investigate the distribution of the fuel droplet size around the bluff-body and the combustion characteristics. The bluff-body is used fur the purpose of increasing the combustion efficiency by stabilizing the flame. Diameters of the bluff-body in this experiment are 6, 8, and 10mm and the impingement angles are $30^{\circ},\;60^{\circ}\;and\;90^{\circ}$. The measurement points were at the distances of 20 and 30 mm axially from the nozzle. The geometry of the bluff-body influenced the spray shape and the combustion characteristics. The SMD was acquired by image processing technique (PMAS), and the mean temperatures were measured by thermocouple. In the condition of ${\theta}=60^{\circ}$, the values of SMD are not greatly varied compared to the other conditions. As the angle of bluff-body was increased, the high temperature region was wider along radial direction. When the air-fuel ratio was larger than 5.2, the NOx concentration was decreased, and an increase in the diameter of the bluff-body decreased the NOx of emission.

• Particle and aerosol research
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• v.8 no.2
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• pp.55-68
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• 2012

Particulate matters (PM) which are collected into a diesel particulate filter (DPF) system have to be periodically removed by thermal oxidation. In this report, we fabricated an electrohydrodynamic-assisted pressure-swirl nozzle to spray diesel droplets finer. Atomization performance of the nozzle was evaluated using both experimental and numerical methods. Two types of nozzle designs, the charge induction type and the charge injection type, were tested. While the former generated diesel droplets of $400\;{\mu}m$ at an applied electric potential over 10 kV, the latter presented the droplets smaller than $23\;{\mu}m$ at an applied electric potential of 8 kV. The numerical simulation results showed that the reduced size of droplets caused higher evaporation of droplets and therefore the increased temperature, which would eventually increase the regeneration performance of the DPF system.