흡입구 유입 유량에 따른 압력 측정 오차에 관한 연구

정석영,이진규 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.4

공기흡입구 카울 표면에 설치된 압력공을 이용하여 전압을 측정하는 기법을 연구하였으며 공기흡입구 유입 유량의 변화에 따라 발생하는 전압 측정의 오차를 측정하고 오차 모델을 구성하였다. 전압 측정용 압력공은 공력적으로 불리한 공기흡입구 카울에 설치되어 공기흡입구 유동에 많은 영향을 받는다. 전압측정의 위치는 수치 해석을 통하여 선정되었으며 받음각에 따라 변함없이 전압이 생성되는 지점을 선택하였다. 풍동 시험을 통하여 전압 오차는 일정 범위의 유량을 벗어나 크거나 작은 경우 발생하는 것으로 측정되었다. 전압 오차는 공기흡입구 유입 유량의 변화에 따라 카울을 따라 이동하는 정체점의 위치에 따라 결정된다고 추정된다. 전압 오차의 보정을 위한 후속 연구를 위하여 풍동 시험 결과를 기반으로 전압 오차 모델을 구성하였으며 유입 유량과 받음각 변화에 따른 전압 오차를 구현하도록 계수를 선택하였다. A technique of pressure measurement was investigated with a pressure hole installed on the cowl of air inlet for total pressure measurement. Determination of pressure hole location was based on numerical analysis results. Wind tunnel test showed that pressure was affected greatly by inlet flow and angle of attack and mach number had little effect on pressure accuracy. Movement of the stagnation point of inlet flow allegedly causes pressure error in low and high inlet flow rate and accurate measurement can be expected only in some range of inlet flow rate where stagnation point of the inlet flow stays on pressure hole. For the purpose of correction, pressure error model and coefficients were selected to match with wind tunnel test results for the variations of inlet flow rate and angle of attack.

Enhancement of film cooling effectiveness using backward injection holes

Park, Sehjin,Jung, Eui Yeop,Kim, Seon Ho,Sohn, Ho-Seong,Cho, Hyung Hee Elsevier 2016 International journal of thermal sciences Vol.110 No.-

<P><B>Abstract</B></P> <P>Film cooling is a cooling method used to protect the hot components of a gas turbine from high temperature conditions. To protect the vanes/blades from excessive thermal stress, backward injection film cooling holes are proposed as one of the methods for the improvement and uniformity of film cooling effectiveness. This study enhanced the film cooling effectiveness on the entire surface using forward and backward injection cylindrical holes with two expected effects: control of vortex interaction between forward and backward injection jets, and the entire surface cooling from near hole exit to far downstream region. The experiments using pressure sensitive paint (PSP) method were conducted to measure the film cooling effectiveness. Four experimental configurations were composed of forward and backward injection cylindrical holes: forward and forward injection holes, backward and backward injection holes, forward and backward injection holes, and backward and forward injection holes. The cylindrical holes were aligned in two staggered rows with pitch (<I>p</I>) of 6<I>d</I> and row spacing (<I>s</I>) of 3<I>d</I>. The injection angles (<I>α</I>) of the cylindrical holes were 35° and 145° for forward and backward injection, respectively. The blowing ratios (<I>M</I>) ranged from 0.5 to 2.0 and the density ratio (<I>DR</I>) was about 1. The results indicated that, at a high blowing ratio, configurations with backward injection holes demonstrated higher and more uniform film cooling effectiveness than with only forward injection holes. Especially, a configuration, composed of forward injection holes in the first row and backward injection holes in the second row, obtained the improved film cooling effectiveness and maintained the high film cooling effectiveness from near hole exit to far downstream region due to weakened vortex strengths of forward and backward injection jets.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Enhancement of film cooling effectiveness by backward injection cylindrical holes. </LI> <LI> Improved cooling performance of a configuration with forward and backward injection. </LI> <LI> Uniform distribution of film cooling effectiveness produced by backward injection. </LI> </UL> </P>

전자-정공 효과(Core-Hole Effect) 적용에 따른 SiO₂ 고압상들의 전자구조 및 O K-edge X-선 Raman 산란 스펙트럼 계산 결과 분석

김훈 ( Hoon Khim ),이유수 ( Yoo Soo Yi ),이성근 ( Sung Keun Lee ) 한국광물학회 2017 광물과 암석 (J.Miner.Soc.Korea) Vol.30 No.2

SiO₂는 지각과 맨틀을 구성하는 풍부한 물질로 고압 상태의 SiO₂ 원자구조를 결정짓는 전자구조적 특성에 대한 상세한 이해는 지구 내부의 탄성과 열역학적 성질에 대한 통찰을 제공한다. SiO₂처럼 경원소(low-z)로 이루어진 지구 물질의 고압상 전자구조는 in situ 고압 XRS (x-ray Raman scattering) 실험을 통해 연구되어 왔다. 하지만 기존의 고압 실험 방법으로는 물질의 국소 원자구조와 XRS 스펙트럼 간 상관관계를 밝히는데 한계가 있다. 이를 극복하고 더 높은 압력에서 존재하는 SiO₂에 대한 XRS 정보를 얻기 위해 밀도 범함수 이론(density functional theory; DFT)에 기반을 둔 제1원리(ab initio) 계산법을 이용한 XRS 스펙트럼 계산 연구들이 진행되고 있다. 비탄성 X-선 산란에 의하여 원자핵 주변 1s 오비탈에 만들어지는 전자-정공(core-hole)은 경원소 물질의 국소 전자구조에 크게 영향을 미치기 때문에 O K-edge XRS 스펙트럼 형태를 계산할 때 중요하게 고려해야 한다. 본 연구에서는 온-퍼텐셜 선형보충파(full-potential linearized augmented plane wave; FP-LAPW) 방법론에 기반하는 WIEN2k 프로그램을 사용하여 α-quartz, α-cristobalite 그리고 CaCl₂-구조를 갖는 SiO₂에 대한 O 원자 전자 오비탈의 부분 상태밀도(partial density of states; PDOS)와 O K-edge XRS 스펙트럼을 계산하였다. 또한, CaCl₂-구조를 갖는 SiO₂의 O 원자 PDOS의 전자-정공 효과의 적용 여부에 따른 차이를 비교하여, 원자핵 부근 전자구조 변화에 따른 PDOS의 피크 세기와 위치 변화가 크게 나타났다는 사실을 확인할 수 있었다. 또한 계산된 각 SiO₂ 구조의 O K-edge XRS 스펙트럼이 각 SiO₂구조에서 계산된 O 원자의 p* 오비탈의 PDOS 결과와 매우 유사한 형태를 갖고 있음을 확인하였다. 이는 O K-edge XRS 스펙트럼이 갖는 대부분의 특징적인 피크들이 O 원자의 점유 1s 오비탈에서 2p* 오비탈로의 전자전이에 기인하기 때문이다. 본 연구의 결과는 SiO2에 대한 정확한 O K-edge XRS 스펙트럼을 계산하는데 있어 전자-정공 효과를 고려해야 한다는 사실을 보여준다. 또한, 실험적으로는 재현이 어려운 고압 환경에 존재하는 CaCl₂-구조를 갖는 SiO₂ (~63 GPa)에 대한 O K-edge XRS 스펙트럼 계산을 통해, 제1원리 계산이 고압상 물질의 물성 연구에 이용될 수 있다는 사실을 보여준다. SiO2 is one of the most abundant constituents of the Earth`s crust and mantle. Probing its electronic structures at high pressures is essential to understand their elastic and thermodynamic properties in the Earth`s interior. The in situ high-pressure x-ray Raman scattering (XRS) experiment has been effective in providing detailed bonding transitions of the low-z materials under extreme compression. However, the relationship between the local atomic structures and XRS features at high pressure has not been fully established. The ab initio calculations have been used to overcome such experimental difficulties. Here we report the partial density of states (PDOS) of O atoms and the O K-edge XRS spectra of α-quartz, α-cristobalite, and CaCl₂-type SiO₂ phases calculated using ab initio calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method. The unoccupied O PDOSs of the CaCl₂-type SiO₂ calculated with and without applying the core-hole effects present significantly distinctive features. The unoccupied O p states of the α-quartz, α- cristobalite and CaCl₂-type SiO₂ calculated with considering the core-hole effect present similar features to their calculated O K-edge XRS spectra. This confirms that characteristic features in the O K-edge XRS stem from the electronic transition from 1s to unoccupied 2p states. The current results indicate that the core-hole effects should be taken in to consideration to calculate the precise O K-edge XRS features of the SiO₂ polymorphs at high pressure. Furthermore, we also calculated O K-edge XRS spectrum for CaCl₂-type SiO₂ at ~63 GPa. As the experimental spectra for these high pressure phases are not currently available, the current results for the CaCl₂-type SiO₂ provide useful prospect to predict in situ high-pressure XRS spectra.

커먼레일 디젤엔진의 연료분사계 최적화 연구

김태규(Tae-Kyu Kim),이웅건(Woong-Gun Lee),강승천(Sung-Chon Kang),이동인(Dong-In Lee) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

The major purpose of this study is to find optimized Injector nozzle's hole-number, hole-hyd.flow and injection pressure, injection-timing in order to achieve their NOx reduction targets while minimizing smoke and fuel economy penalty. The tests were performed on a 6 ℓ Common Rail Diesel Engine to use commercial-vehicle, excavator, wheel-loader, fork-lift truck. In this study, two case of injector nozzle's hole-number(#7, #8) and three case of injector nozzle's hole-hyd.flow(Standard, +7%, -7%) were tested for their relation of NOx, BSFC, smoke by changing injection-pressure, injection-timing. From the test, we find that injector nozzle's hole-number, #8 and hole-hyd.flow, Standard are optimized at this engine. And we find engine performance and emission trend by changing injection-pressure and injection-timing.

LIMIT OF FUEL INJECTION RATE IN THE COMMON RAIL SYSTEM UNDER ULTRA-HIGH PRESSURES

Jianhui Zhao,Leonid Grekhov,Pengfei Yue 한국자동차공학회 2020 International journal of automotive technology Vol.21 No.3

The common rail injection system with higher injection pressure can improve injection characteristics. However, relevant researches for injection characteristics under ultra-high pressures are insufficient. In this article, the results of experiments with a maximum injection pressure of 390 MPa for nine different injectors of four types are presented. The experiment showed the existence of supercritical pressure during injection. At pressures below the supercritical pressure, the injection quantity increases with increasing injection pressure, however, when the injection pressure is over supercritical pressure, the injection quantity does not increase. According to the experiment results, the supercritical injection pressure is about 300 ~ 350 MPa. Under ultra-high pressures, fuel is strongly heated and the local sound velocity decreases, and the adiabatic flow velocity reaches the sound velocity. Under supercritical pressure, the injection rate ceases to increase and even begins to fall. The traditional equations for calculating the injection rate cannot correctly describe the injection under ultrahigh pressures. A new mathematic model with considering the fuel heating for describing the injection quantity of compressible fluid was developed, this model is not only suitable for calculating the injection quantity under ultra-high pressures, but under traditional injection pressures.

SPRAY COLLAPSE IN A SIDE-MOUNT GASOLINE DIRECT INJECTION INJECTOR WITH VARIOUS INJECTION CONDITIONS AND INJECTOR NOZZLE CONFIGURATIONS

박성욱,김희준,양승호 한국자동차공학회 2022 International journal of automotive technology Vol.23 No.3

In this study, the spray collapse in a non-flash boiling condition was studied. Spray collapse can occur in a sidemount gasoline direct injection (GDI) injector because of its narrow hole distance. To investigate the spray collapse, a spray visualization system was constructed with a high speed camera and a metal halide lamp. Spray visualization was conducted at various injection pressures, ambient pressure, and fuel temperature conditions. Moreover, two injectors with a narrow or wide hole pattern were used to observe the effects of the nozzle hole pattern. The central spray developed by spray collapse overtook the plume jet. As the injection pressure increased, the central spray overtook the plume jet earlier; however, the distance from the nozzle tip was not related to the injection pressure. Higher ambient pressure significantly reduced to the time to overtaking by increasing the spray cone angle. Additionally, when the ambient pressure was high, the effect of fuel temperature was negligible; however, when the ambient pressure was close to or less than the fuel saturation pressure, the spray collapse was dramatically accelerated because of the high evaporation rate with flash boiling. The nozzle hole pattern also had a significant effect on the overtaking point. The narrower hole pattern promoted spray collapse by more effectively blocking air flow from the outside to inside spray, which led to changes in the spray tip penetration. However, the velocity at the plume development and central spray was nearly the same, regardless of nozzle hole pattern.

분사 조건이 다공형 GDI 인젝터의 분무 거동에 미치는 영향

박정환(Jeong Hwan Park),박수한(Su Han Park),이창식(Chang Sik Lee),박성욱(Sungwook Park) 한국자동차공학회 2012 한국 자동차공학회논문집 Vol.20 No.2

The purpose of this study is to investigate the overall spray behavior characteristics for various injection conditions in a gasoline direct injection(GDI) injector with multi-hole. The spray characteristics, such as the spray penetration, the spray angle, and the injection quantity, were studied through the change of the injection pressure, the ambient pressure, and the energizing duration in a high-pressure chamber with a constant volume. The n-heptane with 99.5% purity was used as the test fuel. In a constant volume chamber, the injected spray was visualized by the spray visualization system, which consisted of the high-speed camera, the metal-halide lamp, the injector control device, and the image analysis system with the image processing program. It was revealed that the injection quantity was mainly affected by the difference between the injection pressure and the ambient pressure. For low injection pressure conditions, the injection quantity was decreased by the increase of the ambient pressure, while it nearly maintained regardless of the ambient pressure at high injection pressure. According to the increase of the ambient pressure in the constant volume chamber, the spray development became slow, consequently, the spray tip penetration decreased, and the spray area increased. In additions, the circular cone area decreased, and the vortex area increased.

인젝터 노즐 홀 직경의 변화에 따른 DME 커먼레일 연료 분사 시스템의 분무 특성에 관한 연구 II

이세준(Sejun Lee),임옥택(Ocktaeck Lim) 한국자동차공학회 2013 한국 자동차공학회논문집 Vol.21 No.4

DME spray characteristics were investigated about varied ambient pressure and fuel injection pressure using the DME common rail fuel injection system when the nozzle holes diameter is varied. The common rail fuel injection system with DME cooling system was used since DME has properties of compressibility and vaporization in atmospheric temperature. The fuel injection quantity and spray characteristics were measured. The spray analysis parameters were spray shape, penetration length, and spray angle at six nozzle holes. Three types of injector were used, the nozzle holes diameter were 0.166 mm (Injector 1), 0.250 mm (Injector 2), and 0.250 mm with enlargement of orifice hole from 0.6 mm to 1.0 mm (Injector 3). The fuel injection pressure was varied by 5MPa from 35 to 70MPa when the ambient pressure was varied 0, 2.5, and 5MPa. When using Injector 3 in comparison to the others, the DME injection quantity was increased 1.69 ~ 2.02 times. Through this, it had the similar low heat value with diesel which was injected Injector 1. Among three types of injector, Injector 3 had the fastest development velocity of penetration length. In case of spray angle, Injector 2 had the largest spray angle. Through these results, only the way enlargement the nozzle holes diameter is not the solution of DME low heat value problem.

드로우 금형의 에어 벤트홀 수량예측 프로그램개발

황세준(Sejoon Hwang),박원규(Warngyu Park) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

While stamping process, air may be trapped between die and blank and it builds up high pressure. This induces the imperfections on the blank surface and makes extreme high tonnage of punch required to reach home position. To prevent these problems, the air ventilation holes are drilled through the die. But, most of die makers drill air ventilation holes excessively on trial and error basis. The present work has developed a simplified mathematical formulation for computing the pressure of air pocket at given cross-sectional area of air ventilation holes and the pressure of air pocket was compared to commercial CFD code and experiments. The pressure was well agreed with the result of CFD code and experiments. The present work could also calculate the optimum cross-sectional area of the air ventilation hole not to exceed the prescribed maximum pressure of air pocket by using the Bisection method.

단일공 발파에서 생성된 균열망에 작용하는 가스압의 수치해석적 산정

정용훈(Yong-Hun Jong),이정인(Chung-In Lee) 한국암반공학회 2006 터널과지하공간 Vol.16 No.5

발파에 의한 암반의 동적 파괴 과정을 설명하기 위해서는 발생한 폭굉압과 가스압의 작용을 동시에 연구해야 한다. 발파 과정에서 폭굉압과 가스압의 발파공 벽면에의 작용을 동시에 모델화하여 이에 따른 암반과의 상호 작용을 수치해석하는 연구에 앞서, 본 연구에서는 단일 발파공에서 생성된 단일 균열망에서의 가스유동에 미치는 가스압 이력, 균열 길이 그리고 가스압을 산정하기 위해 적용한 상태 방정식의 영향에 대해 분석하였다. 이를 위하여 단일공 발파에 의해 길이 0.01 m, 간극 0.001 m으로 동일한 5개의 균열로 구성된 단일 균열망이 생성되었다고 가정하였다. 또한 지름이 45 mm인 발파공에 지름이 36 mm인 PETN을 장약하였다고 가정하여 수치해석을 수행하였다. 그 결과, 균열망을 구성하는 개별 균열에 작용하는 최대 가스압력과 그 도달시간은 사용 폭약의 특성과 균열망의 기하학적 특성에 의해 결정되는 것으로 나타났다. In order to explain entirely dynamic fracture process induced by blasting in rock mass, it needs to consider detonation pressure and gas pressure acting on blasthole wall simultaneously. In this study, prior to simulating the coupling between gas flow and rock mass, we analyzed effects of gas pressure-time history, length of cracks and equation of state adopted to calculate the gas pressure on the gas flow within a radial fracture created by single-hole blasting. The effects were investigated on two assumptions: (a) the radial fracture was composed of 5 cracks which were 0.01 m in length and 0.001 m in asperity each and (b) the PETN explosive which diameter was 36 ㎜ was charged in a blasthole of 45 ㎜ diameter. It was concluded that the maximum gas pressure and its travel time were dependent on characteristics of charged explosives and geometrical properties of radial fracture.