Keonwoong Lee

Effects of Wall-Injection Length on Spray and Combustion in a Coaxial Porous Injector

The mixing performance of an injector determines the combustion performance of a bipropellant rocket engine. In the previous study, a novel coaxial porous injector concept was developed to improve the mixing performance of a shear coaxial injector. It demonstrated a higher characteristic velocity efficiency than that of a typical shear coaxial injector. To clarify the efficiency-improving mechanism of a coaxial porous injector, the combustion flowfields of both injectors were visualized using a high-speed shadowgraph technique. The effect of geometry factors on the spray core length and the combustion performance as well as the differences in the reactive spray behavior between the coaxial porous injector and the shear coaxial injector were observed. The coaxial porous injector with a different wall-injection length showed higher characteristic velocity efficiencies, shorter spray core lengths, and thicker phase-change patterns at the spray core boundary. Changes in wall-injection length had a nonmonotoni...

Comparison between GOx/Kerosene and GN 2 O/Ethanol Reactive Spray in a Subscale Liquid Rocket Engine

Reactive sprays of two propellant combinations(GOx/kerosene and /ethanol) were observed and compared with each other as a basic research of visualizing supercritical combustion. A shadowgraph imaging method was used to visualize the reactive sprays, and shadowgraph images were converted to density gradient magnitude images to analyse the structure of reactive sprays. The gas-liquid interface of GOx/kerosene spray showed rougher boundary and steeper density gradient near the injector face than the /ethanol at similar combustion chamber pressure. Spray core length was calculated from averaged density gradient magnitude images and it was revealed that spray core length of GOx/kerosene was shorter than that of /ethanol, although momentum flux ratio of GOx/kerosene propellant combination was lower.

Visualizations of Gas-centered Swirl Sprays in Sub to Super Critical Conditions

ABSTRACT The gas-centerd swirl injectors are widely used on the main combustor of large liquid propellant rocket engines. Since the gas-liquid propellants, such as kerosene and oxygen-rich gas combination, are mixed and burned in the high pressure condition over the critic al pressure point, the cold-flow spray test in the atmospheric condition can not represent the actual spray pattern. To observe the near actual spray patterns of gas-centered swirl injector, the high pressure spray chamber and the control system were constructed. The operating sequence was controlled precisely to obtain clear visualization images.초 록 기체중심 스월 인젝터는 대형 액체 로켓 엔진의 주연소기로 광범위하게 사용되고 있다. 케로신과 산소과잉 가스와 같은 기체-액체 추진제들은 임계 압력 이상의 높은 압력 조건에서 혼합, 연소되므로 대기조건에서의 비연소 분무실험은 실제적인 분무 거동을 정확히 재현할 수 없다. 기체중심 스월 인젝터에서 실제 조건과 유사한 분무 패턴을 관측하기 위해서, 고압 챔버와 제어 시스템이 구성되었고 선명한 가시화 결과를 얻기 위하여 실험 과정이 정밀하게 제어되었다.Key Words: Gas-centered Swirl Injector(기체중심 스월 인젝터), Super Critical Spray(초임계 분무), Macroscopic Spray Pattern(거시적 분무 패턴)Received 10 December 2013 / Revised 7 May 2014 / Accepted 15 Ma y 2014

Combustion Performance of a Coaxial Porous Injector using Ethanol/N 2 O Propellant

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.

Analysis of Supercritical Shear Coaxial Jet Using Density Gradient Magnitude

Spray characteristics of single round jet with liquid nitrogen and coaxial spray with liquid nitrogen and gaseous argon were observed. Shadowgraph method was used for spray visualization, and density gradient magnitude image was used to analyse the result. In subcritical condition, irregularity of the jet surface was harder in the coaxial spray. In supercritical condition, diffusion of nitrogen injected from shear coaxial injector was faster than single jet. Jet diameter was induced by averaging images, in supercritical condition, difference of diameter of coaxial jet was rapidly decreased than that of single jet.

Disintegration of Cryogenic Jet in Super-critical Environment

Abstract Sub/supercritical spray experiments were conducted, and cryogenic nitrogen and gaseous argon were selected for simulants.liquid nitrogen and gaseous argon were injected in subcritical case, and supercritical nitrogen and near-critical gaseous argonwere injected in near-critical/supercritical cases. shadowgraph method was used to visualize spray, and analyzed about thebreakup length. The breakup length was measured from numbers of Instantaneous shadowgraph Images from each case, andthey were compared with momentum flux ratios and density ratios. It was observed that the relation between breakup lengthand momentum flux ratio was fitted into former experiment results. and the reasonable constant was suggested about the rela-tion between breakup length and density ratio . 기호설명 d 분사기 액체분사 포스트 내경L 제트의 진행방향 길이J 운동량 플럭스 비아르곤의 질량유량질소의 질량유량P ch 챔버의 압력P cr 임계 압력P G 분사시 아르곤의 압력P L 분사시 질소의 압력ρ i 분사시 질소의 밀도ρ o 분사시 아르곤의 밀도T ch 챔버 온도T cr 임계 온도T G 분사시 아르곤의 온도T L 분사시 질소의 온도 1. 서론 최근의 주된 액체로켓엔진은 고온 고압 환경의 연소실에 극저온 추진제를 분사, 연소시켜 연소실의 압력을올려 그 힘으로 추력을 얻는다. 따라서, 연소실 내부는대부분의 상황에서 추진제의 초임계 온도 및 압력 이상의 온도와 압력을 가진 상태가 되며, 따라서 추진제는대부분 온도가 임계 조건을 만족하지 못하는 아임계 액체 상태에서 초임계 상태로 상변화를 거치며 분사된다. 초임계 유체의 분무 및 연소에 관한 연구는 주로 해외에서 활발하게 이루어지고 있는데, 미국의 플로리다대학교(UFL)