• Journal of Power System Engineering
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• v.13 no.3
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• pp.20-26
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• 2009

디젤기관에서 배출되는 유해배출성분인 NOx(Nitrogen oxides)와 PM(Particulate matter)은 기관 실린더내의 혼합기 분포에 의해 그 생성이 지배된다. 이 때문에 그 유해배출물들을 저감하기 위해서는 연소의 전단계인 혼합기 분포 및 그 생성과정의 해석은 매우 중요하다. 디젤기관에서 노즐로부터 분사된 연료는 주위기체와 혼합기를 형성하는 과정에서 액체에서 기체로 상변화를 동반한다. 따라서 분무의 혼합기형성과정을 해석하기 위해서는 액상과 기상을 동시에 분리하여 계측하는 것이 필요하다. 그러므로 본 연구에서는 디젤분무를 대상으로 Melton 등이 제안한 엑시플렉스(Exciplex) 형광법을 이용하여, 분무의 액상과 기상을 동시에 2차원분리해서 가시화촬영을 행하였다. 그 엑시플렉스 형광법을 이용하여 획득한 이미지에 화상 응용해석을 실시하여 비정상증발디젤분무의 혼합기형성과정에 대한 정보를 얻고자 하였다. 엑시플렉스 형광법을 이용해서 증발분무의 거동측성을 해석한 결과 프랙틸해석을 이용한 분무 흐트러짐(Disturbance)의 평가에서 플랙틸차원은 분사압력의 변화에 관계없이 하나의 값, 약 1.1로 정리 할 수 있고, 그 결과 각 분사압력에 대한 분무 기상외곽곡선(외주)은 거의 동일한 정도의 요철형상을 갖는다.

• Journal of Energy Engineering
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• v.26 no.1
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• pp.28-33
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• 2017

A liquid nitrogen engine is a highly clean power engine, which does not emit any hazardous substances in its fumes. Additionally, it has an advantage over electric vehicles, as its energy density is larger than that of a battery. The use of an existing liquid nitrogen engine is typically limited to the reciprocation type. In this study, the concept of a nitrogen engine equipped with a scroll expander is introduced. The engine's efficiency was shown to increase when the scroll expander was utilized in the engine, while also adding to the simplification of the structure. Therefore, compared to the existing reciprocation-type engine, the engine with the scroll expander has the potential to be both technically and economically more competitive. In this study, the performance of a liquid nitrogen engine equipped with a scroll expander was analyzed while altering the injection pressure profile of liquid nitrogen.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.64-70
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• 2005

The overall results of hot firing tests of fuel-rich gas generator with impinging injector at design and off-design points are described. The gas generator consists of an injector head with impinging injector, a water cooled combustor wall, a turbulence ring to enhance mixing, an instrument ring measuring temperature and pressure and a nozzle. The combustion tests were successfully performed without damage of gas generator. Test results show that the outlet temperature is not dependent on residence time of hot gas within 4～6msec but dependent on chamber pressure. The relation between outlet temperature and combustion efficiency resulting from measured pressure, mass flow rate and area of nozzle throat is shown. The overall O/F ratio is the critical parameter to determine the outlet temperature and the linear correlation between two parameters is established.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.1
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• pp.28-39
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• 2003

Effects of the orifice internal flow such as cavitation and hydraulic flip on transverse injection into subsonic crossflows have been studied. The liquid column breakup length and the liquid column trajectory were measured by changing the orifice diameter (d), the orifice length/orifice diameter (L/d), the injection pressure and the shapes (sharp and round) of orifice entrance, and were compared with previous results. It is found that cavitation bubbles, which occur inside the sharp-edged orifice, make the liquid jet very turbulent and especially in the orifices with L/d ＝ 5 hydraulic flip appear as cavitation bubbles are emitted from the orifice. The breakup length is shorter as cavitation bubbles grows and hydraulic flip appears. However, the liquid column trajectories normalized by the effective diameter and the effective momentum ratio have a similar tendency irrespective of cavitation and hydraulic flip.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.5
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• pp.92-100
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• 2010

Combustion stability rating tests of 75-tonf-class thrust chamber for technology demonstration were carried out at a low pressure. Two kinds of mixing heads were used in this study. One of them has injectors of 631 and the other has injectors of 721. Mixing head with injectors of 631 showed a self-oscillation instability at the chamber pressure of 30 bar. Mixing head with injectors of 721 showed that a high frequency combustion stability was maintained under the same pressure and the same mass flow rate. But mixing head with injectors of 721 generated a self-oscillation instability at the chamber pressure of 20 bar and it was found that stability boundary region was changed due to the configuration of a mixing head from these results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.80-86
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• 2003

An anaysis on the discharge performance of an impinging-type injector for cavitating flow has been conducted by both numerical and experimental method. The predicted discharge coefficient for cavitating flow agrees well with the measured data showing less than 1% discrepancy. For the case of non-cavitating flow analysis, the disagreement between CFD results and the experimental data is 8%. The discharge coefficient for the cavitating flow decreases with decrease in the Reynolds number. On the other hand, it increases slightly as the Reynolds number increases for the non-cavitating flow because of the reduced viscous effect. From the present study, it is confirmed that the fact that cavitation phenomena should be included to predict accurately the discharge performance of injectors for cavitating flow regime. The uniformity of density and velocity magnitude degraded at the injector exit, and the secondary flow strength through the injector orifice accentuated due to cavitation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.1-7
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• 2017

The atomization of a liquid into multiple droplets has many important industrial applications, including the atomization of fuels in combustion processes and coating of surfaces and particles. Ultrasonic atomizing nozzle has a transducer that receives electrical input in the form of a high frequency signal from a power generator and converts that into mechanical energy at the same frequency. Liquid is atomized into a fine mist spray using high frequency sound vibrations. In coating applications, the unpressurized, low-velocity spray reduces the amount of overspray significantly because the droplets tend to settle on the substrate, rather than bouncing off it. The spray can be controlled and shaped precisely by entraining the slow-moving spray in an ancillary air stream using specialized types of spray-shaping equipment. The desired patterns of spray can be obtained using an air stream. To simulate the water mist behavior of an ultrasonic atomizing nozzle using an air stream, the Lagrangian dispersed phase model was employed using the commercial code FLUENT. The effects of the nozzle contraction shape, water droplet size and the pneumatic pressure drop on the spray characteristics were investigated to obtain the optimal condition for coating applications.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.308-318
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• 1988

The liquid disintegration and characteristics of atomization through the swirl nozzle is affected by injection pressure and injection time when the liquid is injected intermittently. These transient phenomena are investigated by electronic controlled-fuel injection nozzle. The effect of injection conditions on disintegration of liquid injected through nozzle is observed photographically by using delay circuit. Droplet size of the element of the sample is measured by the liquid immersion sampling technique. SMD of droplets is varied with time and is decreased as the injection pressure increases. As the injection pressure increases, the maximum diameter of droplet and diameter of droplet which has the maximum droplet number decrease. Spray angle is not affected on injection pressure and change of spray angle with time is associated with needle movement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.9-9
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• 2000

액체 램제트 엔진의 V형 유입구에 3개의 안내깃이 있은 경우에 대하여 유동 해석을 수행하였다. 수치해석에 앞서 본 연구에서는 ONERA에서 발표한 고체 램제트 연소기에 대한 실험 결과를 유동 해석 결과와 비교하여 해석의 정확성을 검증하였다. 안내깃에 의하여 연소실로 유입되는 공기는 유입구 곡관에서 효율적인 흐름을 유지할 수 있고 분사되는 연료의 분포도 제어될 수 있다. 안내깃의 두께가 큰 경우 자칫 유입되는 공기의 흐름을 방해하는 장애물의 역할을 할 수 있으므로 두께의 변화에 대한 영향도 계산하였으나 선정된 안내깃에 의한 연소실에서의 유동특성 변화는 적은 것으로 나타났다. 입구조건을 균일 유동으로 주고 해석한 결과, 연소실에서의 유동은 안내깃의 유무에 따라 큰 영향을 받지 않았다. 그러나 흡입구로 유입되는 공기의 속도 분포는 다양한 비행조건에서 균일하지 않기 때문에 주 유동을 방해하지 않는 안내깃의 설치는 연소실에서의 좀 더 안정된 화염의 생성을 위해 필요하다.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1629-1633
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• 2004

Liquid is commonly introduced as transversal jets in venturi scrubber which is one of the gas cleaning equipments. The jet dynamics such as penetration and breakup is of fundamental importance to the dust-collection efficiency. We have developed a model that can numerically simulate the breakup of the liquid jet in crossflow. This simulation consists of models on liquid column, jet surface breakup, column fracture and secondary droplet breakup. These models have been embedded in the KIVA3-V code. We have calculated such parameters as the jet penetration, jet trajectory, droplet size, velocity field and the volume flux distribution. The results are compared with the experimental data in this paper.