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Title: The unsteady fuel flow response of liquid fuelled gas turbine injector to applied fluctuation
Author: Mo, Ran
ISNI:       0000 0004 7971 0178
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2017
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In the recent years many investigations into combustion instability phenomena have been undertaken. This has been partly driven by the development of lean burn gas turbine combustion systems which are more prone to such instabilities. Most of this previous research was based on the assumption that the effect of liquid fuel flow fluctuations could be ignored. However, work on active combustion control has shown that even small fuel flow variations can be of significant effect. In this thesis, focus is placed on the transient response of the liquid fuel flow issuing from an injector to imposed fluctuations. Flow models that are appropriate to modelling the transient fluid response based on the time scales being considered are firstly introduced and categorized. A fully resolved injector network model was developed according to the actual complex geometry of the injector fuel gallery system. This was validated using rigid column theory and was compared with the experimental results. The elastic and rigid column theory results obtained from this complex model showed that the injector fuel gallery system can be considered as a rigid column. In other words fluid compressibility effects within the injector can be ignored. However, the compressibility of the liquid should be included when the complete fuel injector system (i.e. including a fuel supply pipe) is considered. A further simplification of the fuel injector was conducted based on the conclusion above in which the complex fuel injector geometry was replaced with simple resistive and inertial components. This simplified injector model was evaluated at three operating conditions that corresponded to different operating mass flow rates. The boundary condition effects were investigated using the simplified injector model, with quarter wave and half wave affects being observed in the fuel supply pipe leading to significant unsteady fuel flows through the injector. This boundary condition has no effect on the injector transient coefficient, but does affect the system response. An experimental scheme was developed to measure the transient coefficients of varies injector geometries. Four simplified injector geometries have been tested. Initially a pressure perturbation was imposed on the face of the injector. However, unexpected negative derived inertial lengths were obtained due to mechanical vibration of the test rig. Subsequently improvements were made with upstream pressure perturbations being introduced into the fuel supply system. Using this methodology, acceptable derived inertial injector lengths were obtained over a limited frequency range. The measured inertial lengths of the simplified injector were in reasonable agreement with the injector geometry (allowing for end correction effects) up to a frequency of approximately 300Hz. Similarly, the measured values agreed with the predicted values. In this way, the injector resistive (based on the mean pressure drop) and inertial (based on the injector inertial length) values can be determined.
Supervisor: Not available Sponsor: Rolls-Royce ; EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Engineering not elsewhere classified ; Gas turbines ; Stability ; Fuel