<p>Pressure gain combustion is beneficial for engine cycle efficiency, compactness, and less emissions. In this disseration, two classes of fluid expansions systems were developed to harness power from the high-speed flow delivered by the pressure gain combustor: a compact expansion system and an efficiency expansion system. In addition, a new class of pressure probes for expansion systems is developed.</p> <p>A numerical methodology is carried out to design and characterize these expansion devices and measurement systems via steady and unsteady Reynolds Averaged Navier stokes simulations. Firstly, the compact expansion system is achieved by developing a supersonic axial turbine. Performance of the supersonic axial turbine exposed to fluctuations from a nozzle downstream of a rotating detonation combustor is assessed with an increased level of complexity, including time-resolved stator, time-resolved rotor, and time-resolved turbine stage characterization. Power extraction, damping of fluctuations, and loss budgeting are evaluated. Unsteady heat transfer assessment is performed to investigate the convective heat flux distribution and decomposition. A performance map is constructed to explore the operating limit. Afterwards, the efficient expansion system is achieved by retrofitting an existing subsonic axial turbine. Without redesigning turbine airfoils, the stator endwall contour was modified to integrate the subsonic axial turbine to a diffuser and a rotating detonation combustor. Performance of the retrofitted subsonic axial turbine exposed to fluctuations form a diffuser is evaluated at several frequencies, amplitudes and inlet Mach numbers, with an increased level of model fidelity, including unsteady stator alone, unsteady turbine stage with a reduced model, full unsteady turbine stage assessment. Turbine efficiency, damping of oscillations, and loss budgeting are assessed. A multi-step optimization strategy is utilized to enhance turbine efficiency by improving the endwall contouring. A performance map is created to examine the operating range. Finally, a new type of pressure probes was developed and angular calibration was performed. A whisker-inspired design enabled the reduction of the vortex shedding effect.</p>

Conventional gas turbine combustors operate with a designed drop in pressure over the length of the device. This is desired in order to encourage mixing within the combustor. Compared to this, pulse pressure gain combustors are an alternative to the conventional combustor that produces an increase in static pressure between the inlet and exhaust of the device. The removal of the combustor pressure loss increases the efficiency of the combustion process by increasing the amount of work produced. Many types of pulsed pressure gain combustors exist. Of these, the valveless pulse combustor is the simplest featuring no moving parts. Whilst some research has been conducted into investigating the performance and workings of a pulse combustor, little has been conducted with the view of cooling the combustor. This has been the focus for the research contained herein. The research has focussed on establishing an understanding of the heat transfer characteristics within a pulse combustor tailpipe. This has involved experimental, analytical and computational research on a pulse combustor as well as on a cold-flow model of a pulse combustor tailpipe. This has enabled a study into the feasibility of cooling a pulse combustor to be conducted. The research has found that for conditions where the unsteady velocity amplitude within the cold-flow model of the pulse combustor tailpipe exceeds the mean velocity, an enhancement to the heat transfer coefficient is measured compared to the value expected in a similar non-oscillating flow. When there is no enhancement to the heat transfer coefficient, the cyclic variation of the unsteady heat flux follows the variation of the unsteady pressure within the device. However, at times of enhancement, the instantaneous heat flux structure shows a large deviation from the structure of the pressure field driving the oscillations. This change is shown to be caused by the reversal in the near-wall velocity and may indicate a mechanism for the enhancement in the mean heat flux. The cooling feasibility study showed that with further investigation, it may be possible to cool a pulse combustor within a gas turbine engine.

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The gas turbine engine is an integral component of the global energy infrastructure and, through widespread use, contributes significantly to the emission of harmful pollutants and greenhouse gases. As such, the research and industrial community have a significant interest in improving the thermal efficiency of these devices. However, after nearly a century of development, modern gas turbine technology is nearing its realizable efficiency limit. Thus, using conventional approaches, including increased compression ratios and turbine inlet temperatures, only small future efficiency gains are available at a high cost. If a significant increase in gas turbine engine efficiency is to be realized, a deviation from this convention is necessary. Pressure gain combustion is a new combustion technology capable of delivering a step increase in gas turbine efficiency by replacing the isobaric combustor found in conventional engines with an isochoric combustor. This modification to the engine's thermodynamic cycle enables the loss in stagnation pressure typical of an isobaric combustor to be replaced with an overall net gain in stagnation pressure across the heat addition process. In this work, a pressure gain combustion technology known as the resonant pulse combustor is studied experimentally and numerically to bridge the gap between lab-scale experiments and practical implementations. First, a functional novel active valve resonant pulse combustor was designed and prototyped, thereby demonstrating naturally aspirated resonant operation with an air inlet valve-driven at a fixed frequency. Then, a series of experimental and numerical studies were carried out to increase the pressure gain performance of the combustor, and the performance and applicability of the active valve resonant pulse combustor concept were then experimental demonstrated in atmospheric conditions with both gaseous and liquid hydrocarbon fuels. Finally, the improved active valve resonant pulse combustor's pressure gain and NOX emissions performance was characterized within a high-pressure shroud in a configuration applicable to gas turbine applications and with varied inlet pressures extending up to 3 bar. This study demonstrates the low NOX capability of the pulse combustor concept and provides insight into how the device's performance may scale with increasing inlet pressure, as would exist in a practical application.

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Pulse detonation combustion has been of interest for many years since it offers several advantages over standard deflagrative combustion. In theory, detonative combustion is a better use of fuel compared to deflagrative combustion since less entropy is generated during a detonation. As a result, detonation offers higher pressure and temperature gain across the wave front compared to the comparable deflagration. Since a detonation is a supersonic event which uses a shock to compress and dissociate reactants, a Pulse Detonation Combustor (PDC) is a relatively simple device that does not necessarily require a large compressor section at the inlet. Despite these benefits, using a turbine to extract work from a PDC is a problem littered with technical challenges. A PDC necessarily operates cyclically, producing highly transient pressure and temperature fields. This cyclic operation presents concerns with regards to turbine reliability and effective work extraction. The research presented here investigated the implementation of a pulse detonation diffuser, a device intended to temporally and spatially distribute the energy produced during a detonation pulse. This device would be an inert extension from a baseline PDC, manipulating the decaying detonation front while minimizing entropy production. A diffuser will seek to elongate, steady, attenuate, and maintain the quality of energy contained in the exhaust of a detonation pulse. These functions intend to reduce stresses introduced to a turbine and aid in effective work extraction. The goal of this research was to design, implement, and evaluate such a diffuser using the using conventional analysis and simulated and physical experimentation. Diffuser concepts using various wave dynamic mechanisms were generated. Analytical models were developed to estimate basic timing and wave attenuation parameters for a given design. These models served to inform the detail design process, providing an idea for geometric scale for a diffuser. Designs were simulated in ANSYS Fluent. The simulated performance of each diffuser was measured using metrics quantifying the wave attenuation, pulse elongation, pulse steadying, and entropy generation for each design. The most promising diffuser was fabricated and tested using a detonation tube. Diffuser performance was compared against analytical and computational models using dynamic pressure transducer diagnostics. / Master of Science

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Gas turbines are important for power generation and aircraft engines. Over thepast century, there has been improvements in components of the gas turbine such ascompressors, turbines and nozzles, but very little progress has been made in combustor technology. The combustion still occurs at constant pressure and the only changes made are in terms of its design and mixing of fuel and air streams. These design changes have only allowed minimal improvements in gas turbine efficiency. To achievea substantative improvement in efficiency, it is required to make a technology change such as the introduction of constant volume combustion.<div><br></div><div>In this work, one such constant volume combustion device in the form of wave rotor combustion is studied and further developed for use in gas turbines. Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. In addition, there is also confined high speed turbulent deflagration. If the blades are curved, then the flow undergoes angular momentum change from inlet to outlet, generating shaft work. This will allow maximum extraction of work potential from the wave rotor. In addition, an attempt is made to check the applicability of plasma assisted ignition for wave rotors. </div><div><br></div><div>A computational tool is developed to understand physics of non-axial channelwave rotors. The governing equations are formulated in one dimension through a passage average approach. Shaft work is estimated using conservation of angular momentum and enrgy to verify the working of numerical model. The model shows increase in shaft work with increase in blade curvature, but as the angle is increased, the possibility of ignititing the reacting mixture becomes difficult since it is hard tomove the mixture towards the ignition port. </div><div><br></div><div>An alternate ignition source using plasma discharges is investigated through experiments. Two experiments are developed, one to make ultrafast measurements of plasma properties such as gas heating and lifetime of electronically excited molecules, and a second experiment to understand ignition characteristics of a pin to ring electrode configuration. The experiments show that excited nitrogen which reacts with molecular oxygen to form atomic oxygen is short lived and forms oxygen atoms extremely rapidly. This rapid formation of oxygen atoms assists in fast ignition. The ignition experiment with pin to pin electrode showed that even though there is fast ignition, the propagation speed does not change significantly with pulse repetition frequency. Ignition with pin to ring electrode showed fast ignition and increase inflame speed with pulse repetition frequency. Results show that plasma discharge can be used as an ignition source for wave rotors but will need further investigation.</div><div><br></div><div>The development of computational tool and plasma discharge experiments has provided a solid base for future efforts in wave rotor combustion and design of full scale non-axial wave rotor combustor experiment.</div>

<div>Gas turbine engines have operated on the Brayton cycle for decades, each decade only gaining approximately one to two percent in thermal efficiency as a result of efforts</div><div>to improve engine performance. Pressure-gain combustion in place of constant-pressure combustion in a Brayton cycle could provide a drastic step-change in the thermal efficiency of these devices, leading to reductions in fuel consumption and emissions production. Rotating Detonation Engines (RDEs) have been widely researched as a viable option for pressure-gain combustion. Due to the extremely high frequencies associated with operation of an RDE, the development and application of high-speed diagnostics techniques for RDEs is necessary to further understand and</div><div>develop these devices.</div><div><br></div><div>An application of high-speed diagnostic techniques in a natural gas-air RDE at conditions relevant to land-based power generation is presented. Diagnostics included high-frequency chamber pressure measurements, chemiluminescence imaging of the annulus, and Particle Image Velocimetry (PIV) measurements at the exit plane of the RDE. Results from a case with two detonation waves rotating clockwise (aft looking forward) in the combustor annulus are presented. Detonation surface plots are created from chemiluminescence images and allow for the extraction of properties such as dominant frequency modes and wave number, speed, and direction. The chamber frequency for the case with two co-rotating waves in the chamber is found to be 3.46 kHz and corresponds to average individual wave speeds of 68% Chapman-Jouguet (CJ) velocity. Dynamic Mode Decomposition (DMD) is applied and indicates the presence of two strong detonation waves rotating clockwise and periodically intersecting with weaker, counter-rotating waves in the annulus at certain times during operation. Singular-Spectrum Analysis (SSA) is used to isolate modes corresponding to the detonation frequency in the signals of velocity components obtained from PIV, maintaining instantaneous phase information. Axial and azimuthal components of velocity are observed to remain nearly 180 degrees out of phase. Lastly, approximate angles for the trailing oblique shocks in the combustion chamber are calculated.</div>