Modelling thermo-acoustic instabilities of an anchored laminar flame in a simple lean premixed combustor: including hydrodynamic effects

Luzzato, Charles M.; Assier, Raphael; Morgans, Aimee S.; Wu, Xuesong

doi:10.2514/6.2013-2003

Cited by 3 publications

(3 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The mutual interactions of the flame front kinematics and the hydrodynamic flow field are not accounted for [ 39 ], meaning the fresh mixture flow field above the burner outlet and inside the flame can be treated using a simple model which is independent of the flame evolution. It has been shown that when the G -equation model is combined with a simple incompressible velocity perturbation model in the fresh mixture, complex flame front evolution phenomena, including the ‘pinch-off’ that occurs for strong flow perturbations, can be captured [ 40 , 41 ].…”

Section: Determining the Flame Describing Functionmentioning

confidence: 99%

Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν -gap metric

Li¹,

Morgans²

2016

Proc. R. Soc. A.

View full text Add to dashboard Cite

Combustion instabilities arise owing to a two-way coupling between acoustic waves and unsteady heat release. Oscillation amplitudes successively grow, until nonlinear effects cause saturation into limit cycle oscillations. Feedback control, in which an actuator modifies some combustor input in response to a sensor measurement, can suppress combustion instabilities. Linear feedback controllers are typically designed, using linear combustor models. However, when activated from within limit cycle, the linear model is invalid, and such controllers are not guaranteed to stabilize. This work develops a feedback control strategy guaranteed to stabilize from within limit cycle oscillations. A low-order model of a simple combustor, exhibiting the essential features of more complex systems, is presented. Linear plane acoustic wave modelling is combined with a weakly nonlinear describing function for the flame. The latter is determined numerically using a level set approach. Its implication is that the open-loop transfer function (OLTF) needed for controller design varies with oscillation level. The difference between the mean and the rest of the OLTFs is characterized using the ν-gap metric, providing the minimum required ‘robustness margin’ for an scriptH∞ loop-shaping controller. Such controllers are designed and achieve stability both for linear fluctuations and from within limit cycle oscillations.

show abstract

Section: Determining the Flame Describing Functionmentioning

confidence: 99%

Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν -gap metric

Li¹,

Morgans²

2016

Proc. R. Soc. A.

View full text Add to dashboard Cite

show abstract

“…The DL instability has also been observed experimentally for anchored flames (see Searby, Truffaut & Joulin 2001). A recent preliminary study (Luzzato et al 2013) indicates that its effect on flame-acoustic coupling can be significant in certain cases.…”

Section: R C Assier and X Wumentioning

confidence: 65%

Linear and weakly nonlinear instability of a premixed curved flame under the influence of its spontaneous acoustic field

Assier

2014

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

The stability of premixed flames in a duct is investigated using an asymptotic formulation, which is derived from first principles and based on high-activation-energy and low-Mach-number assumptions (Wu et al., J. Fluid Mech., vol. 497, 2003, pp. 23-53). The present approach takes into account the dynamic coupling between the flame and its spontaneous acoustic field, as well as the interactions between the hydrodynamic field and the flame. The focus is on the fundamental mechanisms of combustion instability. To this end, a linear stability analysis of some steady curved flames is undertaken. These steady flames are known to be stable when the spontaneous acoustic perturbations are ignored. However, we demonstrate that they are actually unstable when the latter effect is included. In order to corroborate this result, and also to provide a relatively simple model guiding active control, we derived an extended Michelson-Sivashinsky equation, which governs the linear and weakly nonlinear evolution of a perturbed flame under the influence of its spontaneous sound. Numerical solutions to the initial-value problem confirm the linear instability result, and show how the flame evolves nonlinearly with time. They also indicate that in certain parameter regimes the spontaneous sound can induce a strong secondary subharmonic parametric instability. This behaviour is explained and justified mathematically by resorting to Floquet theory. Finally we compare our theoretical results with experimental observations, showing that our model captures some of the observed behaviour of propagating flames.

show abstract

“…It has been established that an incompressible flow field assumption is reasonable for modelling the flame response [20,37]. In addition to this, the coupling between the flame kinematics and the flow field itself may be neglected, such that independent forcing functions for #» u may be applied [39,43],…”

Section: Principal Test Casementioning

confidence: 99%

The effect of hydrogen enrichment on the forced response of CH4/H2/Air laminar flames

Lim,

Li,

Morgans

2021

Preprint

View full text Add to dashboard Cite

Hydrogen-enrichment of conventional natural gas mixtures is an activelyexplored strategy for reducing pollutant emissions from combustion. This study investigates the effect of hydrogen enrichment on the unsteady flame response to perturbations, with a view to understanding the implications for thermoacoustic stability. The Level Set Approach for kinematically tracking the flame front was applied to a laminar conical premixed methane / hydrogen / air flame subjected to 2D incompressible velocity perturbations. For hydrogen enrichment levels ranging from 0% to 80% by volume, the resulting unsteady heat release rate of the flame was used to generate the Flame Describing Functions (FDFs). This was performed across a range of perturbation frequencies and levels at ambient pressure. The mean heat release rate of the flame was fixed at Q = 2.69 kW and the equivalence ratio was set to ϕ = 1.08 for all hydrogen enrichment levels. Hydrogen-enrichment was found to shift the FDF gain drop-off to higher frequencies, which will increase propensity to thermoacoustic instability. It also reduced the effective flame time delay. Sensitivity analyses at ϕ = 0.8 revealed that the changes in FDF were driven predominantly by the flame burning speed, and were insensitive to changes in Markstein length.

show abstract

Modelling thermo-acoustic instabilities of an anchored laminar flame in a simple lean premixed combustor: including hydrodynamic effects

Cited by 3 publications

References 23 publications

Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν -gap metric

Feedback control of combustion instabilities from within limit cycle oscillations using H∞ loop-shaping and the ν -gap metric

Linear and weakly nonlinear instability of a premixed curved flame under the influence of its spontaneous acoustic field

The effect of hydrogen enrichment on the forced response of CH4/H2/Air laminar flames

Contact Info

Product

Resources

About