• Title/Summary/Keyword: Break-up Length

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A Study on the Measurement of Break-up Length for the Diesel Sprays (디젤분무의 분열길이 측정에 관한 연구)

  • Jang, S.H.;Ra, J.H.
    • Journal of Power System Engineering
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    • v.3 no.3
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    • pp.22-28
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    • 1999
  • The injected liquid does not break-up instantly after injection for diesel engine. There is some unbroken portion, which is the liquid core(The length of liquid core is called the break-up length) in the spray. If the liquid core is longer than the depth of the bowl in the small DI diesel engine, the liquid core impinges on the surface of the piston. Once the liquid core impinges on the surface, it cannot ignite or burn rapidly and thus prolongs burning time with a degradation in thermal efficiency. The break-up length of a diesel spray in a compressure vessel was measured by an electric resistance method, A voltage was applied between the nozzle and screen, bar, needle electrode inserted at various axial and radial positions into atomizing sprays. As a result, a current flows not only in the region of liquid core but also through the droplets of the spray. It is found that the break-up length measured with screen electrode is overestimated. The break-up length of the spray is found to be proportional to the square root of the density ratio of fuel and surrounding gas. The break-up length of the spray decreases as the injection pressure and the back pressure increase.

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Impinging Atomization of Intermittent Gasoline Sprays (간헐 가솔린 분무의 충돌에 의한 미립화 촉진)

  • 원영호;임치락
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.5
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    • pp.174-181
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    • 1998
  • Experimental and analytical studies are presented to characterize the break-up mechanism and atomization processes of the intermittent- impinging-type nozzle. Gasoline jets passing through the circular nozzle with the outlet diameter of 0.4mm and the injection duration of 10ms are impinged on each other. The impingement of fuel jets forms a thin liquid sheet, and the break-up of the liquid sheet produces liquid ligaments and droplets subsequently. The shape of liquid sheets was visualized at various impinging velocities and angles using the planer laser induced fluorescence (PLIF) technique. Based on the Kelvin-Helmholtz wave instability theory, the break-up length of liquid sheets and the droplet diameter are obtained by the theoretical analysis of the sheet disintegration. The mean diameter of droplet is also estimated analytically using the liquid sheet thickness at the edge and the wavelength of the fastest growing wave. The present results indicate that the theoretical results are favorably agreed with the experimental results. The size of droplets decreases after the impingement as the impinging angle or the injection pressure increase. The increment of the injection pressure is more effective than the increment of the impinging angle to reduce the size of droplets.

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Numerical Simulation of Dam Break Flow using EFDC Model and Parameter Sensitivity Analysis (EFDC 모형을 이용한 댐 붕괴류 수치모의 및 매개변수 민감도 분석)

  • Jang, Chul;Song, Chang Geun
    • Journal of the Korean Society of Safety
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    • v.31 no.4
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    • pp.143-149
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    • 2016
  • In this study, a series of numerical simulation of dam break flow was conducted using EFDC model, and input conditions including cell size, time step, and turbulent eddy viscosity were considered to analyze parameter sensitivity. In case of coarse mesh layout, the propagated length of the shock wave front was ${\Delta}_x$ longer than that of other mesh layouts, and the velocity results showed jagged edge, which can be cured by applying fine grid mesh. Turbulent eddy viscosity influenced magnitude of the maximum velocity passing through gate up to 20% and the cell Peclet number less than 2.0 ensured no numerical oscillations.

The Numerical Study on Prediction of Diesel Fuel Spray Evolution in a Different Types of Nozzle Geometry (노즐 형상에 따른 디젤 연료 분무의 발달 예측에 관한 수치 해석적 연구)

  • Min, Se Hun;Suh, Hyun Kyu
    • Journal of ILASS-Korea
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    • v.22 no.4
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    • pp.169-174
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    • 2017
  • The objective of this study was to verify the experimental and numerical results of spray evolution injected from different types of the nozzle-hole geometries. Spray visualization was taken by high speed camera under the different conditions. For the simulations of spray tip penetration, turbulence, evaporation and break-up model were applied K-zeta-f, Dukowicz and Wave model, respectively. Also, the prediction accuracy of spray tip penetration was increased by varying the spray cone angle. At the same time, the results of this work were compared in terms of spray tip penetration, and SMD characteristics. The numerical results of spray evolution process and spray tip penetration showed good agreement with experimental one.

Studies on the Reducing Methods of Cold Wind Damage of Rice Plant by Installation of Windbreak Net in the Eastern Coastal Area (동해안 냉조풍지대의 방풍망에 의한 수도의 풍해경감방법)

  • 이승필;이광석;최대웅;손삼곤;김칠용
    • KOREAN JOURNAL OF CROP SCIENCE
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    • v.32 no.2
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    • pp.163-172
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    • 1987
  • Results obtained from this study conducted to find the effect of wind-break net on reducing cold wind damage in the eastern coastal cold wind damaged area are summarized as follows. The rice critical safe heading date was up to Aug. 10 in the eastern coastal area, which the frequency of gale Aug. 10 to Sep. 10 is high. The frequencies of westries and cold wind from sea were 25%, respectively, in this area. The effects of wind-break net on reducing wind verocity were 26.9, 34,6% with raising air temperature of 0.4-0.7$^{\circ}C$ and water temperature of 0.3-0.5$^{\circ}C$. The effect of wind-break net was up to 10 time's distance of wind-break net's height from wind-break net. The installation of wind-break inhanced to rice growth, so showed the heading date earlier by 2-5days and increased culm length, no.of panicles per hill and no. of spiklets per panicle. The yield decrease in this area was due to sterilization, poor ripening and light 1,000 grain weight. The yields showed 20-28% increase by installation of wind-break net. The effect of wind-break net was most in the installation plot with wind-break net against cold wind from sea and westries installed in the panicle formation stage.

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RADIAL FLOW AND DROPLETS SPLASH OBSERVED ON A WALL IMPINGEMENT JET (벽면 충돌분무의 반경방향 흐름과 액적 비산에 관한 고찰)

  • KIM, Young-Il
    • Journal of the Korean Society of Industry Convergence
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    • v.3 no.1
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    • pp.37-42
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    • 2000
  • 액체 분무가 벽면의 평평한 면에 충돌할 때의 거동에 대해 실험을 통하여 조사하였다. 각 분사노즐과 벽면까지의 거리 그리고 분사 속도에 있어서 충돌점에서의 액체 액막의 비산 거동과 평면에서의 액막의 흐름에 대하여 관찰하였다. 충돌점에서 비산하는 액적의 비산율을 정량적으로 측정하였다. 분사속도가 증가에 의해 충돌 거동은 5개의 영역으로 분류되며, 분사속도가 증가하면 비산율도 증가하게 된다. 또한, 충돌거리가 분무의 분열점보다 길때의 분사량의 약 반 정도가 비산하게 되는 결과가 얻어졌다.

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Related-Key Attacks on Reduced Rounds of SHACAL-2 (축소 라운드 SHACAL-2의 연관키 공격)

  • Kim Jongsung;Kim Guil;Lee Sangjin;Lim Jongin
    • Journal of the Korea Institute of Information Security & Cryptology
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    • v.15 no.3
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    • pp.115-126
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    • 2005
  • SHACAL-2 is a 256-bit block cipher with up to 512 bits of key length based on the hash function SHA-2. It was submitted to the the NESSIE project and was recommended as one of the NESSIE selections. In this paper, we present two types of related-key attacks called the related-key differential-(non)linear and the related-key rectangle attacks, and we discuss the security of SHACAL-2 against these two types of attacks. Using the related-key differential-nonlinear attack, we can break SHACAL-2 with 512-bit keys up to 35 out of its 64 rounds, and using the related-key rectangle attack, we can break SHACAL-2 with 512-bit keys up to 37 rounds.

Effect of Night-break Period on Growth and Anthesis of Orostachys japonicus (암기중단 처리시간에 따른 바위솔의 생장과 개화)

  • 강진호;류영섭;조부근
    • KOREAN JOURNAL OF CROP SCIENCE
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    • v.41 no.2
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    • pp.236-242
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    • 1996
  • Orostachys japonjcus, called Wasong in herb medicine, has been artificially cultivated as an anti-tumor medicinal. The experiment was done to examine the effect of night-break periods imposed immediately before its bolting time on its morphological, flowering-related characters and fraction dry weights. After a plant was grown in a 15cm plastic pot containing a 2:1 soil:Peat moss mixture for about 3 months, three different night-break periods (0.5, 1 and 2 hours) around midnight were treated from Aug. 24. to compare with the natural daylength. The plants were sampled 6 times by 2-week interval after the treatments. Plant height and inflorescence length of all the treatments inclined with time lapse after the treatment and were shorter in 2 hour night-break due to slow increment than in the other treatments, while stem diameter showed reverse result. All the treatments except 2 hour night -break were nearly same in fraction, shoot and total dry weights per plant; two hour night-break treatment had greater leaf and bract weight from 6 weeks, greater stem, shoot and total weights from 2 weeks and greater root weight from 4 weeks but did less floret weight after the treatment. Although florets on the inflorescence were formed in 2 hour night-break treatment, flowering florets and flowering plants never occurred. In the other treatments showed the similar response, however, more florets appeared from 2 weeks, flowering florets was sharply increased from 6 weeks and flowering plants were reached up to 100% from 6 to 8 weeks after the treatment. Inflorescence length or number of total florets per plant in 2 hour night-break was positive-correlated to all the fraction dry weights except that those of natural daylength was not done, meaning that its artificial cultivation should permit bolting to secure more shoot dry matter.

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Visualization of Doublet Impinging Jet Spray in Supercritical Mixed Hydrocarbon Fluid (초임계 탄화수소계열 혼합유체의 이중 충돌 제트 분무 가시화)

  • Song, Juyeon;Choi, Myeung Hwan;An, Jeongwoo;Koo, Jaye
    • Journal of the Korean Society of Propulsion Engineers
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    • v.25 no.4
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    • pp.53-58
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    • 2021
  • Based on surrogate model, a hydrocarbon mixture was analyzed by visualizing the impinging break up mechanism in subcritical and supercritical conditions. Decane and methylcyclohexane with different critical pressures and temperatures were selected as experimental fluids. The impinging injector was installed inside the chamber, and the spray was visualized through a speed camera in subcritical and supercritical conditions. The injection condition of the mixture and chamber was kept constant at Pr(P/Pc) = 1, and Tr(T/Tc) was increased from 0.48 to 1.02. As Tr increased, the spray angle increased, and the sheet length decreased as the properties of the mixture reached each critical point. In addition, when the mixture approached the near critical point, it was shown that the change in density gradient was largely observed out of the impinging break up mechanism.

Effect of Wind Break on the Early Growth of Pinus thunbergii at Saemangum Sea-wall (새만금 방조제에서 곰솔의 초기 생장에 미치는 방풍 시설 설치 효과)

  • Kim, Jeong-Hwan;Lim, Joo-Hoon;Seo, Kyung-Won;Jeong, Yong Ho;Um, Tae-Won
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.15 no.4
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    • pp.210-218
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    • 2013
  • The sea breeze shows different characteristics compared to land breeze, such as high wind speed and more rapider shift period. One of the major factors affecting plant early growth is wind speed. In the early growth stage, tree growth-rates rise with decreasing wind speed. Thus, the study was performed to identify wind break effects on wind characteristics and tree growth. The wind break used in this study was about 130 meters length and 3 meters height, made up with poly-ethylene (with 40% openness). We installed one vane and fifteen anemographs at three different heights (1, 2 and 3 meters) on the inner and outer wind break areas. The wind characteristic and plant growth data were collected from Jun. 2011 to Oct. over 2012. The wind rose of the Saemangum seawall area presented the north (21.5%) and it was followed by north-west (18.1%), east (14.9%) and north-east (13.7%) and the remainder with other directions. Wind speeds at height were different. The tree height was 159.6 cm at inside and 129.6 cm at outside. The diameter at root-collar was 36.9 mm at inside and 32.6 mm at outside from wind break.