• 한국분무공학회지
• /
• 제9권3호
• /
• pp.42-49
• /
• 2004

The present article investigates the influence of droplet drag models on predictions of diesel spray behaviors under ultra-high injection pressure conditions. To consider drop deformation and shock disturbance, this study introduces a new hybrid model in predicting drag coefficient from the literature findings. Numerical simulations are first conducted on transient behaviors of single droplet to compare the hybrid model with earlier conventional model. Moreover, using two different models, extensive numerical calculations are made for diesel sprays under ultra-high pressure sprays. It is found that the droplet drag models play an important role in determining the transient behaviors of sprays such as spray tip velocity and penetration lengths. Numerical results indicate that this new hybrid model yields the much better conformity with measurements especially under the ultra-high injection pressure conditions.

• 대한기계학회논문집B
• /
• 제22권5호
• /
• pp.661-671
• /
• 1998

It is unavoidable that the fuel spray impinges on the wall of piston cavity in a compact high-pressure D.I. diesel engine. Therefore the characteristics of impinging spray are the very significant information on the consideration and the simulation of its combustion processes including the formation mechanism of exhaust emission and the design of the combustion chamber. In this paper, the numerical simulation was performed to study the characteristics of impinging spray. The spray-wall impingement model used is Watkins and Park's model. Calculation parameters are the inclination angles and the ambient pressures. As the inclination angle increases, the impinging spray develops mainly to the direction of the downstream and scarcely flows to that of the upstream. The shape on the wall of the impinging spray is the circle in the case of the normal impingement, while it is the ellipse in that of the oblique impingement. As the ambient pressure increases, the growth of impinging spray on the wall in the radial direction decreases owing to the increase in the resistance of the ambient.

• 한국수소및신에너지학회논문집
• /
• 제27권6호
• /
• pp.727-736
• /
• 2016

Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

• 한국자동차공학회논문집
• /
• 제13권6호
• /
• pp.187-194
• /
• 2005

The objective of this study is to validate the hybrid breakup model and the vaporization model for GDI spray analysis at vaporization and non-vaporization conditions. 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 vaporization process is modeled by using modified Abramzon & Sirignano model. The exciplex fluorescence method was used for comparing the calculated results with the experimental ones. The experiment and the calculation were performed at the ambient pressures of 0.1 MPa, 0.5 MPa and 1.0 MPa and the ambient temperature of 293K and 473K.

• 한국항공우주학회지
• /
• 제36권10호
• /
• pp.1011-1016
• /
• 2008

KIVA3V를 이용하여 모형 가스터빈 연소기에서 Jet-A의 분무와 연소에 관한 수치해석을 하였다. 연소기 형상은 6개의 희석홀을 가지며, 스월효과를 고려하였다. 연소 특성을 해석하기 위해 열적 NO 발생을 고려하였다. 다양한 분무각에 대해서 Jet-A 증기, 화염온도 분포와 NO 발생량에 대하여 비교하였다. 분무각이 커질수록 1차 영역에서 연료 증기가 비교적 고르게 나타나게 되며 증발이 더욱 빠르게 되고, 주변 기체와 연료 증기 사이의 혼합이 증가한다. 그 결과 고온부가 넓게 나타나게 되고, 이에 의해 열적 NO 발생이 증가한다.

• 한국분무공학회지
• /
• 제22권4호
• /
• pp.175-184
• /
• 2017

The numerical investigation on the effects of water-mist characteristics has been carried out for the fire suppression mechanism. The FDS are used to simulate the interaction of fire plume and water mists, and program describes the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The numerical model is consisted of a rectangular enclosure of $L{\times}W{\times}H=1.5{\times}1.5{\times}2.0m^3$ and a water mist nozzle that be installed 1.8 m from fire pool. In the present study, the parameters of nozzle for simulation are the droplet size and the spray velocity. The droplet size influences to fire flume on fire suppression more than the spray velocity because of the effect of the terminal velocity. The optimal condition for fire suppression is that the droplet size and the spray velocity are $100{\mu}m$ and 20 m/s respectively.

• 한국분무공학회지
• /
• 제3권2호
• /
• pp.24-33
• /
• 1998

The characteristics of liquefied butane spray are expected to be different from conventional diesel fuel spray, because a kind of flash boiling spray is expected when the back pressure is below the saturation vapor pressure of the butane(0.23MPa at $25^{\circ}C$). An accumulator type pintle injector and its fuel delivery system has been simulated in ruder to give injection pressure, needle lift and rate of fuel injected. The governing equation were solved by finite difference metho. The injection duration was controlled by solenoid valve. Spray behaviors such as a transient spray tip penetration, spray angle and SMD were calculated based on the empirical correlations in case that the back pressure is both above the vapor pressure of the butane and below that of butane. When the back preassure is below the vapor pressure of the fuel, conventional correlation is modified to represent the effect of flash boiling.

• 한국자동차공학회논문집
• /
• 제5권6호
• /
• pp.120-127
• /
• 1997

A diesel engine is one of the major prime movers owing to its high thermal efficiency. But due to the recent attention for the environmental pollution, the emissions of diesel engine became a important problem. So it is needed to understand the characteristics of diesel spray injected into a combustion chamber. Because the diesel combustion is strongly controlled by a fuel spray injected into a combustion chamber. This study provides the informations for the diesel spray with the atmospere condition in combustion chamber by PMAS. As the result, the spray tip penetration and angle is increased with the increase of spray pressure and nozzle diameter. And the comparisions between the measured outline of the free-spray and the calculated model have been conducted and obtained the resonable results.

• 대한기계학회논문집
• /
• 제13권1호
• /
• pp.140-152
• /
• 1989

본 논문에서는 소형 고속 디젤 분무의 반경 방향의 연류 농도 분포를 고려한 비균질 분무의 분무 선단 도달 거리에 대한 관계식을 유도하고, 비정상 분무인 디젤 분무의 분사 차압-시간 곡선을 입력시킴으로써, 분사 초기 뿐 아니라 전 분사 기간의 분무 선단 도달 거리를 예측할 수 있는 새로운 모델을 제안하여 실험치와 비교 분석하였다. 그리고 분사각과 분열장의 무차원 실험식을 도출하여 계산에 사용하였고 분무 선단 도달 거리의 천이점과 분열장에 대하여 고찰하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.974-979
• /
• 2003

This study aimed to analyze spray characteristics and the ambient flow field in the mixture preparation state of the premixed combustion stage. It is very important to understand the spray characteristics and the fuel injection conditions in direct injection diesel engine because the emission gas compositions from diesel engines are related to spray formation processes of the premixed combustion stage. The numerical simulation was performed using the STAR-CD which is a commercial CFD code. Computed results of the transient high pressure diesel spray were compared with experimental results of the same spray injection condition in the constant volume chamber. The results show that spray patterns of numerical simulation agree with this experimental results comparatively.