동축형 전단 분사기의 액적분포 균일도 및 혼합성능을 개선하기 위해 고안한 액체로켓 엔진용 동축형 다공성 분사기의 개발에 앞서 다공성재를 분사기에 적용하기 위해 다공성재를 통과하는 압축성 유체의 압력강하 특성을 파악하였다. Non-Darcy 유동의 압력강하는 점성력과 관성력으로 인한 손실을 포함하는 Forchheimer 방정식을 이용하여 도출할 수 있으며, 이 때 다공성재의 형상인자인 투과율과 관성력의 영향을 나타내는 Ergun 상수를 이용하여 다공성재를 통과하는 압축성 유체의 압력강하를 예측할 수 있다. 본 연구에서는 다공성재의 압력강하 특성을 나타내는 투과율와 Ergun 상수를 작동유체의 압력강하에 대한 함수로 나타내었으며, 최종적으로 이를 일반화하여 pore의 크기에 따라 압력강하를 예측할 수 있는 관계식을 도출하였다.
To research and develop a high performance injector for LRE, it needs not only cold flow test, but also investigations of combustion performance, optimization of cyclogram and thermo-fluid dynamical characteristics of combustion flow field through hot-fire test. In this study, hot-fire test of LOX-CH4 coaxial swirl injector has been carried out using lab-scale hot fire test stand which can supply and control cryogenic propellant. Ignition and continuous combustion for LOX-GCH 4 propellant of 0.19 kg/s total mass flowrate and 2.80 O/F Ratio was achieved through cyclogram optimization. The mean combustion chamber pressure and thrust were measured as approximately 1.43 MPa and 38.7 kgf respectively.
Observations on the near-nozzle behavior of an unsteady fuel spray through single cylindrical hole nozzle were made by phase Doopler anemometer and microphotographs. At the edge of the spray, droplet velocities have shown wave-like behavior. The average droplet velocity peaked during needle opening and closing. Droplet sizes tended to be small on the edge of spray. The near-nozzle spray angle taken from the micropho-tographs was time-dependent, even though it increased with gas-to-liquid density ratio as expected. The near-nozzle spray angle was the greatest on the initial stage arid decreased to a relatively constant value after about one third of the total injection duration regardless of the ambient gas conditions. even in the near-vaccum condition. The wider near-nozzle spray angle in the early stage is due to the flow characteri-stics inside the nozzle rather than aerodynamic interactions. However, once the spray was established, aerodynamic interactions are essential in the near-nozzle atomization.
액체 중심 전단 동축 인젝터는 액체 제트를 기체 제트의 전단력으로 분열시켜 미립를 향상시키며, 이러한 2유체 전단 동축 인젝터는 고효율 연소 시스템, 산업용 코팅, 반도체 세정 등에 사용이 가능하다. 본 연구에서는 기체 전단력에 의한 초기 액주 분열 과정과 인젝터 기하학적 형상 변화에 따른 미립화 특성을 파악하기 위해 3.0 bar 이하의 분사 압력 조건에서 액체 중심형 전단 동축 인젝터를 사용하여 실험하였다. 저압 분사 조건에서 분무되는 액체 제트는 액주 형태로 분무되며, 이러한 액주는 기체 제트의 전단력에 의해 수 msec 이내에 액적으로 미립화된다. 액체 제트의 미립화 특성과 관련된 변수 중 SMD는 액체 중심 노즐 주위의 환형 기체 노즐 토출구 직경이 증가 할수록 감소하였으며, 기체 제트의 유량이 증가함에 따라 SMD가 감소하는 경향을 나타내었다.
Micro gas turbine engine is well known as a power plant of unmanned aerial vehicle and a small scale emergency generation system and also, it is significant as initial research of large gas turbine and educational purpose of gas turbine. Many sort of Micro gas turbine test set for education is produced by several manufacturers, but all of the engine control system of them is separated with data acquisition system; moreover, the engine control algorithms are inaccessible and related variables could not be collected. In this investigation, the Integrated Modifiable Test Rig which has modifiable engine start-up, drive and situational control logics is developed by LabVIEW with I/O devices and it provides wide experimental applicability to studies of dynamic characteristics of fuel system and combustion instability.
The gas jet from a coaxial porous injector for two-phase flows is discharged radially from the porous surface, which encloses the center liquid jet. Several hot-firing test using ethanol/nitrous oxide propellants was conducted to analyze the effect of oxidizer/fuel ratio on the combustion performance, and the uncertainty analysis was performed for the results. The characteristic velocity was affected by oxidizer/fuel ratio similarly with the results of CEA calculation except that the maximum characteristic velocity was appeared in the stoichiometric ratio. The characteristic velocity efficiency was increased as the oxidizer/fuel ratio increases.
The measurements of velocities of internal flow in a scaled-up nozzle were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. The investigated length to diameter ratio(L/d) of the orifice were 1, 3, 4, 5 and 8, and inlet radius to diameter ratio(rｏ/d) were 0 and 0.5. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds number ranging between 15,000 and 28,000, and L/d ranging between 1 and 8 in sharp and round inlet nozzle. The turbulent intensity and turbulent kinetic en-ergy at exit in a sharp inlet nozzle were higher than that in a round inlet nozzle. For sharp inlet nozzle, fluctuating velocities near exit were decreased with increasing L/d.
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