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Intermittency route to combustion instability in a laboratory spray combustor
Samadhan A. Pawar, R. Thejas Vishnu, ,
Published in American Society of Mechanical Engineers (ASME)
2016
Volume: 138
   
Issue: 4
Abstract
In the present study, we investigate the phenomenon of transition of a thermoacoustic system involving two-phase flow, from aperiodic oscillations to limit cycle oscillations. Experiments were performed in a laboratory scale model of a spray combustor. A needle spray injector is used to generate a droplet spray having one-dimensional velocity field. This simplified design of the injector helps in keeping away the geometric complexities involved in the real spray atomizers. We investigate the stability of the spray combustor in response to the variation of the flame location inside the combustor. Equivalence ratio is maintained constant throughout the experiment. The dynamics of the system is captured by measuring the unsteady pressure fluctuations present in the system. As the flame location is gradually varied, self-excited high-amplitude acoustic oscillations are observed in the combustor. We observe the transition of the system behavior from low-amplitude aperiodic oscillations to large amplitude limit cycle oscillations occurring through intermittency. This intermittent state mainly consists of a sequence of high-amplitude bursts of periodic oscillations separated by low-amplitude aperiodic regions. Moreover, the experimental results highlight that during intermittency, the maximum amplitude of bursts, near to the onset of intermittency, is as much as three times higher than the maximum amplitude of the limit cycle oscillations. These high-amplitude intermittent loads can have stronger adverse effects on the structural properties of the engine than the low-amplitude cyclic loading caused by the sustained limit cycle oscillations. Evolution of the three different dynamical states of the spray combustion system (viz., stable, intermittency, and limit cycle) is studied in three-dimensional phase space by using a phase space reconstruction tool from the dynamical system theory. We report the first experimental observation of type-II intermittency in a spray combustion system. The statistical distributions of the length of aperiodic (turbulent) phase with respect to the control parameter, first return map and recurrence plot (RP) techniques are employed to confirm the type of intermittency. © 2016 by ASME.
About the journal
JournalJournal of Engineering for Gas Turbines and Power
PublisherAmerican Society of Mechanical Engineers (ASME)
ISSN07424795
Open AccessNo
Concepts (16)
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    Atomization
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    Combustion
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    Dynamical systems
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    Fuel systems
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    Phase space methods
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    Two phase flow
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    Velocity
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    ACOUSTIC OSCILLATION
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    Combustion instabilities
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    DIMENSIONAL PHASE SPACES
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    GEOMETRIC COMPLEXITY
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    Limit cycle oscillation (lco)
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    Phase space reconstruction
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    Statistical distribution
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    THERMOACOUSTIC SYSTEMS
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    Combustors