High-Frequency Flame Oscillation Observed at a Coaxial LOX/LH2 Injector Element

Nunome, Yoko; Takahashi, Mamoru; Kumakawa, Akinaga; Miyazaki, Kazuhiro; Yoshida, Seiji; Onga, Tadaoki

doi:10.2514/6.2008-4848

Cited by 10 publications

(5 citation statements)

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“…Nunome et al [11] reported that an LOX post exit taper could influence the characteristics of combustion instability in an LOX − GH 2 combustor. However, the effects of LOX post exit tapers on the flowfields of coaxial jets, such as mixing enhancement, have not yet been studied in detail.…”

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confidence: 99%

Effects of Injector Geometry on Cryogenic Shear Coaxial Jets at Supercritical Pressures

Tani

Teramoto

Okamoto

2015

Journal of Propulsion and Power

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For shear coaxial injectors, which are widely used in liquid oxygen-gaseous hydrogen rocket engines, the key parameters that characterize injector geometry are the recess length, taper angle, and wall thickness of the liquid oxygen post, which is the inner tube of the coaxial injector. In the present study, the effects of the recessed length and taper angle of the liquid oxygen post on cryogenic coaxial jets at supercritical pressures were experimentally investigated. The large-scale structure and mixing enhancement of cryogenic nitrogen and gaseous helium coaxial jets were evaluated using a high-speed backlighting technique. Instantaneous backlit images revealed that the dark core, which is believed to be dense nitrogen, exhibited sinusoidal forms induced by the presence of the outer helium jets. However, the sinusoidal oscillations were less influenced by the injector geometry. The mixing enhancement of coaxial jets was evaluated with respect to the dark-core length and the jet spread angle. The recessed liquid oxygen post enhanced the mixing of cryogenic nitrogen when the recess length was sufficiently large, which suggests that a recess of a certain length is required to improve the mixing of cryogenic coaxial jets at supercritical pressures. Because the decrease in the dark-core length with the recessed length was consistent with the increase in the jet spread angle at the injector exit, the mixing enhancement caused by the recess can be regarded as a result of an improvement in the mixing between the inner and outer jets in the recessed region. The effects of the liquid oxygen post exit taper on the mixing enhancement were more significant than those of the recess. The decrease in the dark-core length with the inner-toouter momentum flux ratio (J number) is consistent with the relevant empirical correlation at supercritical pressures. Therefore, the mixing enhancement caused by the liquid oxygen post exit taper can be considered the result of an increase in the J number, rather than the result of giving azimuthal velocity to the cryogenic nitrogen jet at the liquid oxygen post exit. NomenclatureDe = outer diameter of the liquid oxygen post Di = inner diameter of the liquid oxygen post Do = inner diameter of the outer tube h = wall thickness of the liquid oxygen post L recess = recess length of the liquid oxygen post L taper = tapered length of the liquid oxygen post V = velocity θ taper = exit-taper angle of the liquid oxygen post ρ = density

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confidence: 99%

Effects of Injector Geometry on Cryogenic Shear Coaxial Jets at Supercritical Pressures

Tani

Teramoto

Okamoto

2015

Journal of Propulsion and Power

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“…The coupling mechanism was therefore described as injection-driven: the instabilities occur when the frequency of the chamber 1T mode matches to the second longitudinal mode of the LOX post [8]. A connection of LOX post acoustics to the driving of combustion instabilities is a phenomenon not specifically associated with the BKD design, but has also been reported for other LOX/H2 experiments [6,11] and even full-scale main stage engines as the J-2S [4] and the recent Japanese LE-X [7]. Also for the propellant combination LOX/CH4 examples of LOX injection-coupling can be found [12,13].…”

Section: Introductionmentioning

confidence: 75%

“…For the propellant combination oxygen-hydrogen flame visualization is usually made with OH* chemiluminescence in the UV range at around 308 nm. High-speed flame radiation imaging has also widely been used to study acoustic-flame interaction in rocket engines [11,[19][20][21][22]. However, recent analysis of the flame emission spectra of hydrogenoxygen flames at different pressure levels by Fiala et al revealed some issues of OH* radiation at the extreme conditions of LPREs, as strong self-absorption and thermal excitation [23][24][25].…”

Section: Operating Conditionsmentioning

confidence: 99%

High-Speed Flame Radiation Imaging of Thermoacoustic Coupling in a High Pressure Research Thrust Chamber

Armbruster

Hardi

Suslov

et al. 2018

2018 Joint Propulsion Conference

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This work addresses the nature of supercritical hydrogen-oxygen flame coupling to acoustics through visualization under conditions representative of upper stage rocket engines. A research thrust chamber which shows self-excited combustion instabilities for certain operating conditions was used. Previous analysis proved that the instabilities are connected to injector acoustics. In this study a small optical access window was mounted in the chamber wall. High-speed flame radiation imaging of OH* and blue wavelengths has been applied in order to analyze the acoustic-flame interaction of one of the 42 flames. Dynamic mode decomposition results for a case with 80 bar chamber pressure showed that the flame dynamics are strongly influenced by the LOX injector acoustics, whereas for a 50 bar chamber pressure load point no flame response to injector acoustics was observed. A potential source of acoustic excitation for the oxygen injectors based on hydrodynamic effects is consistent with the contradictory behavior of the two load points.

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“…A team led by Wahnainen performed extensive full-scale testing using down-ramping of H 2 temperature to map stability margins as a function of injection parameters 16,17 . Nunome et al 18 have also used the temperature ramping technique of Wanhainen to characterize the stability limits of their single-element, lab-scale combustor. It remains unclear whether this is H 2 temperature effect arises from an intrinsic or injection-coupled mechanism.…”

Section: Introductionmentioning

confidence: 99%

Study of LOx/H2 Spray Flame Response to Acoustic Excitation in a Rectangular Rocket Combustor

Hardi

Oschwald

Dally

2013

49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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This work is focused on understanding how intrinsic processes may be involved in driving high frequency combustion instabilities. The response of an experimental rocket combustor to both unperturbed and acoustically excited conditions at four different operating points was studied. The combustor has a rectangular cross-section with acoustic forcing, five shear coaxial injection elements running cryogenic oxygen-hydrogen (LOx/H 2 ), and optical access. The operating points comprise two different chamber pressures and two different hydrogen injection temperatures. The chamber pressures of 40 and 60 bar allow the influence of sub-and supercritical LOx, respectively, to be studied. The H 2 injection temperatures of ~290 K and ~50 K were selected since low H 2 temperature has long been thought to influence the stability of LOx/H 2 engines. Combustor response was compared between the four operating points under both undisturbed conditions, and forced resonance of the 1L and 1T modes. The measures used to compare combustor response were acoustic spectra, modal acoustic energy distribution, LOx jet atomization behavior, flame displacement, and chemiluminescent emission intensity. None of the parameters compared revealed a significant difference in response between the four operating points. There were two exceptions of interest. The first was in the distribution of unperturbed acoustic energy to the 1L and 1T modes. The content of both modes was lower at 60 bar, regardless of H 2 temperature, except the 1T mode was more energetic at 60 bar when using low temperature H 2 . The second was the greater decrease in intact LOx core length under 1T-mode excitation with low temperature H 2 . Both of these observations may be related to the historic tendency for transverse mode instability with decreasing H 2 temperature. Nomenclature c = bulk sound speed in combustion chamber δʹ = acoustic particle displacement D = diameter of oxygen injector (LOx post) I = OH* emission intensity Iʹ = unsteady OH* emission intensity Ī = time averaged OH* emission intensity J = injection momentum flux ratio L = length of intact LOx core M = mass flow rate N = response factor ω = acoustic frequency pʹ = acoustic pressure amplitude P cc = combustion chamber pressure 2 qʹ = unsteady heat-release rate ROF = oxidizer-to-fuel mixture ratio ρ = bulk density in combustion chamber T = injection temperature u = injection velocity uʹ = acoustic (particle) velocity VR = injection velocity ratio

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High-Frequency Flame Oscillation Observed at a Coaxial LOX/LH2 Injector Element

Cited by 10 publications

References 0 publications

Effects of Injector Geometry on Cryogenic Shear Coaxial Jets at Supercritical Pressures

Effects of Injector Geometry on Cryogenic Shear Coaxial Jets at Supercritical Pressures

High-Speed Flame Radiation Imaging of Thermoacoustic Coupling in a High Pressure Research Thrust Chamber

Study of LOx/H2 Spray Flame Response to Acoustic Excitation in a Rectangular Rocket Combustor

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