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Investigation of combustion instabilities in annular combustors combining injector dynamics and flame describing functions determined in simplified configurations

Abstract : This thesis addresses some of the central issues in combustion dynamics of annular systems, essentially focusing on understanding, interpreting, and predicting combustion instabilities coupled with azimuthal modes. These modes are the most detrimental among those encountered in gas turbines and aero-engines as they correspond to the lowest eigenfrequencies where the flame is most sensitive to incoming disturbances. The work specifically considers the case where the flames established in the combustor are formed by a spray of liquid fuel and on injection systems generating a swirling flow, idealizing those found in practical applications. Systematic experiments are carried out on a multiple-injector annular combustor (MICCA-Spray), allowing full optical access to the combustion region and equipped with multiple microphones for identifying the pressure field. These are complemented with measurements of flame describing functions (FDFs) using a single-sector combustor (SICCA-Spray) and another facility featuring an array of three injectors (TICCA-Spray) to better represent the flame environment and boundary conditions corresponding to the annular case. This combination of experiments is used to explore the effects of injection geometry and operating parameters on the occurrence of combustion instabilities. The domains of instability are documented for three fuel types (premixed propane and air, heptane and dodecane) and different values of injector head loss and swirl number. In addition, the instabilities are also found to be sensitive to the location of the atomizer with respect to the injector outlet. Several questions are considered in this work, including the possibility of representing the response of a multi-dimensional flame using the FDF framework and methods to suitably determine FDFs for the class of injectors used, which are weakly transparent to acoustic waves. The comparison between measured FDFs in the single sector and the linear array of three injectors is used to reveal the limitations of data corresponding to an isolated flame in representing the dynamics of flames surrounded by neighboring flames. The data interpretation based on low-order modeling indicates that many of the features observed experimentally can be predicted by making use of measured FDFs. This, however, requires that the swirling injectors be suitably represented by an injector impedance and that the damping rate be estimated. The analysis underlines the importance of the swirling injector parameters and injection conditions on the occurrence of combustion instability and provides guidelines in sorting out their influence.
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https://hal.archives-ouvertes.fr/tel-03741349
Contributor : Preethi Rajendram Soundararajan Connect in order to contact the contributor
Submitted on : Monday, August 8, 2022 - 1:28:42 PM
Last modification on : Wednesday, August 10, 2022 - 3:22:32 AM

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  • HAL Id : tel-03741349, version 2

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Preethi Rajendram Soundararajan. Investigation of combustion instabilities in annular combustors combining injector dynamics and flame describing functions determined in simplified configurations. Reactive fluid environment. Université Paris-Saclay, 2022. English. ⟨tel-03741349v2⟩

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