On the phase between pressure and heat release fluctuations for propane/hydrogen flames and its role in mode transitions

Handle URI:
http://hdl.handle.net/10754/599064
Title:
On the phase between pressure and heat release fluctuations for propane/hydrogen flames and its role in mode transitions
Authors:
Hong, Seunghyuck; Shanbhogue, Santosh J.; Speth, Raymond L.; Ghoniem, Ahmed F.
Abstract:
This paper presents an experimental investigation into mode-transitions observed in a 50-kW, atmospheric pressure, backward-facing step combustor burning lean premixed C3H8/H2 fuel mixtures over a range of equivalence ratios, fuel compositions and preheat temperatures. The combustor exhibits distinct acoustic response and dynamic flame shape (collectively referred to as "dynamic modes") depending on the operating conditions. We simultaneously measure the dynamic pressure and flame chemiluminescence to examine the phase between pressure (p') and heat release fluctuations (q') in the observed dynamic modes. Results show that the heat release is in phase with the pressure oscillations (θqp≈0) at the onset of a dynamic mode, while as the operating conditions change within the mode, the phase grows until it reaches a critical value θqp=θc, at which the combustor switches to another dynamic mode. According to the classical Rayleigh criterion, this critical phase (θc) should be π/2, whereas our data show that the transition occurs well below this value. A linear acoustic energy balance shows that this critical phase marks the point where acoustic losses across the system boundaries equal the energy addition from the combustion process to the acoustic field. Based on the extended Rayleigh criterion in which the acoustic energy fluxes through the system boundaries as well as the typical Rayleigh source term (p'q') are included, we derive an extended Rayleigh index defined as Re=θqp/θc, which varies between 0 and 1. This index, plotted against a density-weighted strained consumption speed, indicates that the impact of the operating parameters on the dynamic mode selection of the combustor collapses onto a family of curves, which quantify the state of the combustor within a dynamic mode. At Re=0, the combustor enters a mode, and switches to another as Re approaches 1. The results provide a metric for quantifying the instability margins of fuel-flexible combustors operating at a wide range of conditions. © 2013 The Combustion Institute.
Citation:
Hong S, Shanbhogue SJ, Speth RL, Ghoniem AF (2013) On the phase between pressure and heat release fluctuations for propane/hydrogen flames and its role in mode transitions. Combustion and Flame 160: 2827–2842. Available: http://dx.doi.org/10.1016/j.combustflame.2013.07.001.
Publisher:
Elsevier BV
Journal:
Combustion and Flame
KAUST Grant Number:
KUS-110-010-01
Issue Date:
Dec-2013
DOI:
10.1016/j.combustflame.2013.07.001
Type:
Article
ISSN:
0010-2180
Sponsors:
The authors would like to acknowledge the King Abdullah University of Science and Technology for their support of this research. This work was funded by the KAUST Grant, number KUS-110-010-01. We also thank the reviewers for their constructive remarks on the paper.
Appears in Collections:
Publications Acknowledging KAUST Support

Full metadata record

DC FieldValue Language
dc.contributor.authorHong, Seunghyucken
dc.contributor.authorShanbhogue, Santosh J.en
dc.contributor.authorSpeth, Raymond L.en
dc.contributor.authorGhoniem, Ahmed F.en
dc.date.accessioned2016-02-25T13:52:11Zen
dc.date.available2016-02-25T13:52:11Zen
dc.date.issued2013-12en
dc.identifier.citationHong S, Shanbhogue SJ, Speth RL, Ghoniem AF (2013) On the phase between pressure and heat release fluctuations for propane/hydrogen flames and its role in mode transitions. Combustion and Flame 160: 2827–2842. Available: http://dx.doi.org/10.1016/j.combustflame.2013.07.001.en
dc.identifier.issn0010-2180en
dc.identifier.doi10.1016/j.combustflame.2013.07.001en
dc.identifier.urihttp://hdl.handle.net/10754/599064en
dc.description.abstractThis paper presents an experimental investigation into mode-transitions observed in a 50-kW, atmospheric pressure, backward-facing step combustor burning lean premixed C3H8/H2 fuel mixtures over a range of equivalence ratios, fuel compositions and preheat temperatures. The combustor exhibits distinct acoustic response and dynamic flame shape (collectively referred to as "dynamic modes") depending on the operating conditions. We simultaneously measure the dynamic pressure and flame chemiluminescence to examine the phase between pressure (p') and heat release fluctuations (q') in the observed dynamic modes. Results show that the heat release is in phase with the pressure oscillations (θqp≈0) at the onset of a dynamic mode, while as the operating conditions change within the mode, the phase grows until it reaches a critical value θqp=θc, at which the combustor switches to another dynamic mode. According to the classical Rayleigh criterion, this critical phase (θc) should be π/2, whereas our data show that the transition occurs well below this value. A linear acoustic energy balance shows that this critical phase marks the point where acoustic losses across the system boundaries equal the energy addition from the combustion process to the acoustic field. Based on the extended Rayleigh criterion in which the acoustic energy fluxes through the system boundaries as well as the typical Rayleigh source term (p'q') are included, we derive an extended Rayleigh index defined as Re=θqp/θc, which varies between 0 and 1. This index, plotted against a density-weighted strained consumption speed, indicates that the impact of the operating parameters on the dynamic mode selection of the combustor collapses onto a family of curves, which quantify the state of the combustor within a dynamic mode. At Re=0, the combustor enters a mode, and switches to another as Re approaches 1. The results provide a metric for quantifying the instability margins of fuel-flexible combustors operating at a wide range of conditions. © 2013 The Combustion Institute.en
dc.description.sponsorshipThe authors would like to acknowledge the King Abdullah University of Science and Technology for their support of this research. This work was funded by the KAUST Grant, number KUS-110-010-01. We also thank the reviewers for their constructive remarks on the paper.en
dc.publisherElsevier BVen
dc.subjectCombustion dynamicsen
dc.subjectFlame-vortex interactionsen
dc.subjectMode transitionsen
dc.subjectPhase between pressure and heat releaseen
dc.subjectRayleigh's criterionen
dc.subjectStrained consumption speeden
dc.titleOn the phase between pressure and heat release fluctuations for propane/hydrogen flames and its role in mode transitionsen
dc.typeArticleen
dc.identifier.journalCombustion and Flameen
dc.contributor.institutionMassachusetts Institute of Technology, Cambridge, United Statesen
kaust.grant.numberKUS-110-010-01en
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