• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.4
• /
• pp.425-432
• /
• 2004

The objective of this study is a qualitative comparison between line-integrated OH chemiluminescence(OH$\^$*/) image and its Abel inverted image to investigate the flame structure at different phase of the oscillating pressure field. PIV(Particle Image Velocimetry) measurements were conducted under non-reacting conditions to see the global flow structure and NOx emission was measured to investigate the effect of fuel-air premixing on combustion instability and emission characteristics. Experiments were carried out in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas. Combustion instabilities in present study exhibited a longitudinal mode with a dominant frequency of ∼341.8㎐, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instability occurred. Results gave an insight about the location where the strong coherence of pressure and heat release existed. Also an additional information on active control to suppress the combustion instabilities was obtained. For lean premixed combustion, strong correlation between OH$\^$*/ and NOx emissions was expected largely due to the exponential dependence of thermal NOx mechanism on flame temperature.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.13 no.3
• /
• pp.50-57
• /
• 2009

A gas mechanical pulsator is developed for the study of combustion instabilities in various combustors such as LRE combustor. First, it shows that the mass flow rates and the perturbation frequencies can be successively controlled by the inlet pressure and the rotating speed of a rotating disk with many holes. Second, the device is used as an acoustic amplification source as a substitute for the speaker in the previous acoustic tests and its results show almost the same resonant frequency and damping characteristics compared with the previous results. In conclusion, the result shows that it can be used as a substitute for a speaker in the studies of LRE combustion instabilities, which has a flow and no limitation of amplification, and a device for making a perturbation source in gas flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.1
• /
• pp.40-47
• /
• 2013

The similarity in internal flow of solid and hybrid rocket suggests that hybrid rocket combustion can be susceptible to instability due to vortex sheddings and their interaction. This study focuses on the evolution of interaction of vortex generated in pre-chamber with other types of vortex in the combustor and the change of combustion characteristics. Baseline and other results tested with disks show that there are five different frequency bands appeared in spectral domain. These include a frequency with thermal lag of solid fuel, vortex shedding due to obstacles such as forward, backward facing step and wall vortices near surface. The comparison of frequency behavior in the cases with disk 1 and 3 reveals that vortex shedding generated in pre-chamber can interact with other types of vortex shedding at a certain condition. The frequency of Helmholtz mode is one of candidates resulting to a resonance when it was excited by other types of oscillation even if this mode was not discernable in baseline test. This selective mechanism of resonance may explain the reason why non-linear combustion instability occurs in hybrid rocket combustion.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.2
• /
• pp.179-185
• /
• 2008

Simulating combustion tests have been performed to elucidate the effect of baffle gaps on the optimal damping characteristics in liquid rocket combustors where coaxial injectors are installed. Amplitude of pressure oscillation in model combustion chamber and the combustion stability margin are used to quantify the damping capacitance of baffles. Satisfactory agreement has been achieved with the results of cold acoustic tests. Present results have shown that the optimal gap for high acoustic damping capacity has also the large combustion stability margin in simulating combustion tests. Therefore, the present results can be utilized to determine the baffle length and optimal gap in full-scaled rocket combustors.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.50 no.11
• /
• pp.783-789
• /
• 2022

In a recent study, it was observed that the combustion gas entering the post chamber of a hybrid rocket contains vortices with very small size and high frequency characteristics. In addition, it was observed that small vortices collided with the nozzle wall to create a counter-flow, resulting in additional combustion with ignition delay. This study investigated the physical relationship between ignition delay induced by the counter-flow and the formation of beating pressure. To do this, a newly modified model was proposed by including ignition delay in the existing energy kicked oscillator model proposed by Culick. Numerical results show that the ignition delay is an important factor in determining the occurrence of the combustion pressure beats through the periodic formation of thermoacoustic coupling. In addition, when the ignition delay was reduced by increasing the post chamber length, the phase difference between the energy kick and the pressure generation was increased, the periodic pressure beats did not occur at all.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.267-270
• /
• 2002

Combustion instability, which is one of the most undesirable phenomena in the development of liquid Propellant rocket engine, can cause serious damage to the rocket itself, and must be evaded by all means. Unfortunately, KSR-III rocket went through the combustion instability during engine start at the propulsion test article No.2. To resolve the problem, time sequence has been changed, and the baffle system has been applied. In consequence of the change, stable combustion was achieved.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.594-596
• /
• 2010

Hot-firing tests were performed on a sub-scale gas generator for development of a 75 ton-class liquid rocket engine. This paper deals with the analysis results of low-frequency combustion instability that encountered during combustion tests of the gas generator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.11
• /
• pp.931-938
• /
• 2002

Combustion dynamics of a dry low NOx gas turbine have been measured by utilizing a dynamic pressure measurement system. The software part of the measurement system, implemented with a commercial general-purpose DASYLab version 5.6 code, basically acquires combustion dynamics signals, performs the FFT analysis, and displays the results. The gas turbine often experiences momentary combustion instability, especially when its combustion mode changes. It is found that the measurement system developed in the study may outperform the other commercial dynamic pressure measurement system. The developed system currently serves to monitor the combustion dynamics of the gas turbine.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2012.05a
• /
• pp.28-30
• /
• 2012

A mechanical pulsator is manufactured for study of combustion instabilities in a model chamber with impinging-jet injectors. Artificial disturbance is generated by the device and thereby, artificial instability can be examined experimentally. A sample F(fuel)-O(dxidizer)-O-F impinging-jet injector is adopted for the test. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions. Pressure fluctuation data, which is obtained from the dynamic pressure transducers installed in combustion chamber, is analyzed.

• Journal of ILASS-Korea
• /
• v.24 no.2
• /
• pp.58-65
• /
• 2019

A 3D FEM (Finite Element Method) based Helmholtz solver has been commonly used to characterize fundamental acoustic behavior and investigate dynamic instability features in many combustion systems. In this approach, a geometrical simplification of the target system has been generally made in order to reduce computational time and cost because a real combustor and fuel nozzle have a very complicated flow passage. The feasibility of these simplifications is quantitatively investigated in a small aero gas turbine nozzle in term of acoustic characteristics. It is found that the simplification in a nozzle geometry during the 3D FEM analysis process has no great influence on the acoustic modeling results, while the calculation complexity can be improved for a similar modeling accuracy.