• Journal of the Korean Society of Propulsion Engineers
• /
• v.11 no.2
• /
• pp.37-46
• /
• 2007

In this study, combustion fields of the end-burning hybrid combustor with tangential oxidizer injectors are examined. Momentum ratio of oxidizer is used as a main parameter to analyse the combustion efficiency with temperature, pressure, swirl velocity and mixture fraction field. It was found that as momentum ratio decreases the overall combustion efficiency is enhanced with the pressure field being insensitive to momentum ratio keeping quasi-uniform distribution. Irrespective to the momentum ratio, annular hot region commonly occurred in the upper combustion chamber where this phenomenon was left for a future improvement to be followed.

• Journal of Mechanical Science and Technology
• /
• v.15 no.1
• /
• pp.117-124
• /
• 2001

This paper presents turbulent characteristics of an impinging F-O-O-F type injector in which fuel ad oxidizer impinge on each other to atomize under the different momentum ratio. Water was used as an inert simulant liquid instead of fuel and oxidizer. The droplet size and velocity in the impinging spray flow field were measured using a PDPA. The gradient of the spray half-width(b$_2$) along the long-axis direction declined throughout the entire spray flow field with increasing the momentum ratio from 1.19 to 6.48. However, the gradient of the half-width(b$_1$) along the short-axis direction decreased with increasing the momentum ratio. The turbulence intensity and turbulent kinetic energy were converged into the center of the center of the initial region with increasing the momentum ratio. As the momentum ratio increased from MR=1.19 to MR=6.48, the turbulent shear stress decreased. The results of this study can be used for the design of an impinging type injector for liquid rackets.

• 한국연소학회:학술대회논문집
• /
• 2013.06a
• /
• pp.47-49
• /
• 2013

Entrainment length and recirculation ratio that are important factors of flameless combustion systems were analyzed by injection conditions using three dimensional numerical simulation. As a result, the entrainment length increased with an increase of momentum ratio and distance of between nozzle. Also, in case of increasing in momentum of oxidation, recirculation ratio was increased and the average temperature was decreased.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.2
• /
• pp.509-518
• /
• 1995

A study for the flame stability and the combustion characteristics of coaxial diffusion flame was conducted. The fuel employed was natural gas. The experimental variables were rim thickness of fuel tube, blockage ratio of the outer diameter of fuel tube to the inner diameter of air tube, and momentum ratio of fuel to air. It was consequently found that the stability in the neighborhood of the fuel rim depended on the rim thickness, especially in the case of above 3 mm, and that the stable region of the flame extended remarkably due to the formation of recirculation zone above rim. The effect of the blockage ratio on the flame stability was found to be minor in the case of above 3 mm of rim thickness. Between the momentum ratio 2 and 3, the stable flame zone was widely established as well good combustion. With increasing the fuel-air momentum ratio, axial velocity, turbulence intensity, and Reynolds stress increased.

• Journal of ILASS-Korea
• /
• v.25 no.3
• /
• pp.126-131
• /
• 2020

Throttleable rocket engines are in high demand due to the diversification of space missions. Pintle injector is known to be suitable for throttleable rocket engines, because of its high efficiency in overall thrust zone. In this study, the relationship between spray angle of a throttleable pintle injector and total momentum ratio based on hot fire test conditions was investigated. As a result, the spray angle in 100% and 60% throttling level is higher than the spray angle obtained by the case which considers only propellant mass flow rate, owing to higher total momentum ratio (TMR). The results of this study may be useful for predicting spray angle in hot fire test.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.21 no.8
• /
• pp.43-52
• /
• 2022

The vibration characteristics of a hammer press are important parameters for machine design and production control. In this study, a counterblow hammer press was mathematically modelled as a mass-spring-damper system in order to analyze its vibration characteristics. The forging efficiency was theoretically derived as a function of the mass ratio, momentum ratio, and the coefficient of restitution And the effects of the mass ratio, momentum ratio and the restitution coefficient on the forging efficiency were also investigated for two particular cases of the unit mass ratio and unit momentum ratio. Additionally, the vibration responses of the counterblow hammer press due to the ram colliding impact were analyzed, and the force transmitted to the foundation through the mounting unit was determined.

• Journal of ILASS-Korea
• /
• v.19 no.4
• /
• pp.167-173
• /
• 2014

The spray characteristics of Gas-Centered Swirl Coaxial Injector was investigated that there were different characteristics with or without gas flow. As gas flow was accelerated, the momentum of gas was transferred to the momentum of liquid in the low liquid Reynolds number. Therefore, the axial velocity of liquid was increased and the measured value was smaller than without gas flow. However, in the high momentum flux ratio, the momentum transfer hardly occurred and the results had constant values. As the recess length was increased, the mixing area of gas and liquid also was increased, the results were decreased.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.4
• /
• pp.25-32
• /
• 2020

A numerical study on combustion instabilities in a model combustor was conducted with various momentum flux ratios. Five ratios are calculated based on an actual operating condition of rocket engine. As momentum flux ratio increases, the spreading angle on the injector outlet decreases. And, as increase of axial momentum flux, pressure fluctuation decreases inside the combustor. By using dynamic mode decomposition method, the acoustic modes inside the combustor are identified. Combustion stabilities are analyzed by comparing the damping coefficient of the 2^nd longitudinal mode.

• Journal of ILASS-Korea
• /
• v.18 no.3
• /
• pp.140-145
• /
• 2013

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 argon were injected in near-critical/supercritical cases. shadowgraph method was used to visualize spray, and analyzed about the breakup length. The breakup length was measured from numbers of Instantaneous shadowgraph Images from each case, and they were compared with momentum flux ratios and density ratios. It was observed that the relation between breakup length and momentum flux ratio was fitted into former experiment results. and the reasonable constant was suggested about the relation between breakup length and density ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.11a
• /
• pp.321-325
• /
• 2008

In this paper, heat transfer changes due to the shock/boundary layer interaction were investigated on surfaces where secondary jet are injected. With an infra-red thermography, surface temperature was measured and the measured data was used to obtain the convective heat transfer. Heat transfer is enhanced with increment of momentum ratio. And normal injection case has a higher heat transfer value than that of 15 degrees inclined injection case. Secondary injection momentum ratio and injection angle affect the surface heat transfer distribution.