High Pressure LOx/H2 Combustion and Flame Dynamics

Smith, Joshua; Suslov, Dmitry; Oschwald, Michael; Haidn, Oskar; Bechle, M.

doi:10.2514/6.2004-3376

Cited by 14 publications

(17 citation statements)

References 17 publications

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“…Interestingly, results published in a LOX/GH2 (i.e., liquid oxygen/ gaseous hydrogen) single-element coaxial jet fired-engine work by Smith et al [15] also are consistent with the Davis and Chehroudi's view described above that high rms values for the dark-core length, specifically at subcritical and low velocity ratios, may lead to or cause combustion instability. In their work, Smith et al swept the engine from the ignition period into three consecutive steady-state phases of supercritical (phase 1), near-critical (phase 2), and subcritical (phase 3) chamber pressures, each sufficiently long for adequate measurements and allowing 2-4 s of transition in between phases.…”

Section: Discussionsupporting

confidence: 73%

Physical Hypothesis for the Combustion Instability in Cryogenic Liquid Rocket Engines

Chehroudi¹

2010

Journal of Propulsion and Power

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In this work, the author would like to portray a sketch of a fluid dynamical picture to describe the coupling nature/ strength between the chamber acoustics and the injectors. This new perspective is achieved through a physically intuitive argument combined with previously published test results for two popular injector designs, namely, coaxial and impinging jets. For the impinging jet injectors, it is shown that the dynamic behavior of the dark-core (or breakup) zone for each jet, their lengths and thicknesses, has a profound impact on injector sensitivity to disturbances in its surrounding. This information is used to offer a possible explanation for the trends seen on the Hewitt stability plot in impinging jet injectors. Nomenclature d j = jet diameter from a hole d n = hole diameter of the injector L C;Pth = average liquid core length P th = threshold chamber pressure P ch = chamber pressure l = liquid density g = gas density T ch = chamber temperature V = average liquid jet exit velocity = impinging jet included half-angle

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Section: Discussionsupporting

confidence: 73%

Physical Hypothesis for the Combustion Instability in Cryogenic Liquid Rocket Engines

Chehroudi¹

2010

Journal of Propulsion and Power

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“…Interestingly, results published in a LOX/GH2 (i.e., liquid oxygen/gaseous hydrogen) single-element coaxial-jet fired engine work by Smith et al [11] (DLR group) also are consistent with the Davis and Chehroudi's view described above that high RMS values for the dark-core length, specifically at subcritical and low velocity ratios, may lead to or cause combustion instability. In their work, Smith et al swept the engine from the ignition period into three consecutive steady-state phases of supercritical (phase 1), near-critical (phase 2), and subcritical (phase 3) chamber pressures, each sufficiently long for adequate measurements and allowing 2-4 seconds of transition in between phases.…”

Section: Discussionsupporting

confidence: 75%

“…Peak-to-Peak chamber pressure oscillations for the V-test, showing a minimum value at a chamber pressure equal to the critical point of the oxygen. Smith et al [11].…”

Section: Peak-to-peak Pressure Amplitudes (%P Ch )mentioning

confidence: 99%

A Unified Approach on Combustion Instability in Cryogenic Liquid Rockets (Preprint)

Chehroudi

2008

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)Air Force Research Laboratory (AFMC) AFRL/RZS SPONSOR/MONITOR'S Pollux Drive NUMBER(S)Edwards AFB CA 93524-7048 AFRL-RZ-ED-TP-2008-581 DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution unlimited (PA #09014). SUPPLEMENTARY NOTESFor presentation at the 47 th AIAA Aerospace Sciences Meeting and Exhibit, Orlando, FL, 5-8 January 2009. ABSTRACTIn this work, the author would like to portray a sketch of a unified physical picture to describe the coupling nature/strength between the chamber acoustics and the injectors. This new perspective is achieved through a physically intuitive argument combined with previously published test results for two popular injector designs, namely, coaxial and impinging jets. For the impinging-jets injectors, it is shown that the dynamic behavior of the dark-core (or breakup) zone for each jet, their lengths and thicknesses, has a profound impact on injector "sensitivity" to disturbances in its surrounding. This information is used to offer a possible explanation for the trends seen on the Hewitt stability plot in impinging-jet injectors. In this work, the author would like to portray a sketch of a unified physical picture to describe the coupling nature/strength between the chamber acoustics and the injectors. This new perspective is achieved through a physically intuitive argument combined with previously published test results for two popular injector designs, namely, coaxial and impinging jets. For the impinging-jets injectors, it is shown that the dynamic behavior of the dark-core (or breakup) zone for each jet, their lengths and thicknesses, has a profound impact on injector "sensitivity" to disturbances in its surrounding. This information is used to offer a possible explanation for the trends seen on the Hewitt stability plot in impingingjet injectors.

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“…These dark regions are believed to be due to the presence of dense oxygen. In previous experiments conducted at supercritical pressures [13,[15][16][17], the dark core was observed to have a cloud-like appearance rather than an appearance of liquid atomization. This suggests that cryogenic nitrogen diffused in a manner similar to turbulent mixing in variable-density single-phase jets.…”

Section: A Snapshots Of Cryogenic Coaxial Jetsmentioning

confidence: 90%

“…At supercritical pressures, surface tension and phase changes between liquid and gas diminish. As a result, the oxygen in a combustor no longer experiences liquid atomization but rather diffuses directly through turbulent mixing, in a manner similar to that observed in turbulent single-phase jets [13][14][15][16][17][18][19]. Thus, the effects of injector geometry on liquid-gas coaxial jets do not necessarily correspond to those on coaxial jets at supercritical pressures.…”

mentioning

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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High Pressure LOx/H2 Combustion and Flame Dynamics

Cited by 14 publications

References 17 publications

Physical Hypothesis for the Combustion Instability in Cryogenic Liquid Rocket Engines

Physical Hypothesis for the Combustion Instability in Cryogenic Liquid Rocket Engines

A Unified Approach on Combustion Instability in Cryogenic Liquid Rockets (Preprint)

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

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