Flame Response to Equivalence Ratio Fluctuations — Relationship between Chemiluminescence and Heat Release

Shreekrishna,; Acharya, Vishal; Lieuwen, Tim

doi:10.1260/1756-8277.5.4.329

Cited by 7 publications

(1 citation statement)

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“…(30). For the combustor configuration considered in this study, the inlet is choked, thereby u ≈ 0, while both p and u are finite at the outlet of the combustor, where the burned gas exits to an exhaust trench of dilution air, as described in Section 3.3.1.…”

Section: Modified Form Of the Extended Rayleigh Criterionmentioning

confidence: 99%

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

Hong

Shanbhogue

Speth

et al. 2013

Combustion and Flame

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This paper presents an experimental investigation into mode-transitions observed in a 50-kW, atmospheric pressure, backward-facing step combustor burning lean premixed C 3 H 8 /H 2 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 (θ qp ≈ 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 θ qp = θ c , at which the combustor switches to another dynamic mode. According to the classical Rayleigh criterion, this critical phase (θ c ) 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 R e = θ qp /θ c , which varies between 0 and 1. * Corresponding author. 77 Massachusetts Avenue, Room 3-344, Cambridge MA 02139, USA. Fax: +1-617-253-5981. E-mail: ghoniem@mit.edu Preprint submitted to Combustion and Flame June 27, 2013 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 R e = 0, the combustor enters a mode, and switches to another as R e approaches 1. The results provide a metric for quantifying the instability margins of fuel-flexible combustors operating at a wide range of conditions.

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Section: Modified Form Of the Extended Rayleigh Criterionmentioning

confidence: 99%