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Gasoline Direct Injection (GDI) engines have been considered to be the key enabler for reducing the CO2 emission from gasoline-powered vehicles. Compared to Port Fuel Injection (PFI) engines, GDI engines realize a higher compression ratio, a lower intake temperature and the absence of throttling which will deliver higher volumetric efficiency and lower fuel consumption. However, due to the reduced time for fuel atomization and the possibility of fuel impingement, GDI engines will inherently generate more Particulate Matter (PM) emissions than PFI engines. Previous research demonstrated that GDI engines typically emit one order of magnitude more PM than PFIs. Therefore, the number-based measurement of PM emissions from GDI engines is essential, for engine researchers and manufacturers to meet the number-based PM regulations in the near future. This thesis undertakes to investigate: a) the effects of the after-treatment (Three-Way Catalyst) and various engine operational parameters, such as injection and ignition timing, injection strategy and valve timing on the PM emissions; b) the characteristics of GDI PM emissions using a range of gasoline/ethanol blends; c) The compositional information for GDI-generated PM emissions, i.e. the PM mass fractions in different volatility ranges. The first objective was achieved by using a Cambustion Ltd Differential Mobility Spectrometer 500 (DMS500) to simultaneously derive the PM size-resolved number concentrations and mass concentrations in the range of 5-1000 nm. The second objective was addressed by using the DMS500 together with other instruments such as a Photron high-speed camera, a Cambustion Ltd fast Flame Ionization Detector (FID). The third objective was realized by using Thermo-Gravimetric Analysis (TGA). These experiments are amongst the first of their kind and may well provide vehicle manufacturers and the fuel industry with useful data for PM control and abatement. Data acquisition (DAQ) systems for two test engines, namely, a V8 GDI engine and a single-cylinder optical access engine, have been developed in LabVIEW to facilitate recording various experimental data at different sampling rates (1Hz to 300 kHz). The DAQ system in the single-cylinder engine is also capable for communicating with the engine controlling system to enable automatic data logging. A controlled automatic dilution system has been developed for taking filter samples in a way that is consistent with emissions legislation.

In modern gas turbine engines, film cooling is extensively used to cool the components exposed to the hot mainstream gas path. In implementing film cooling on modern gas turbine engines, the trailing edge film poses a particularly challenging design problem. From an aerodynamic point of view, the trailing edge of a blade is designed to be as thin as possible. However, this conflicts with the implementation of the cooling design. The most common method of film cooling the trailing edge is via late pressure surface discrete film cooling holes. Another method of cooling the trailing edge is by using discrete pressure surface slots. This thesis documents a comparative aerodynamic and heat transfer study of three trailing edge cooling configurations. The study was carried out using a large scale, low speed wind tunnel situated at the Southwell Laboratory. The three trailing edge cooling configurations considered were as follows. First is the common late pressure film cooling of the trailing edge via discrete film cooling holes. This configuration is designated as datum configuration. Second is the pressure surface slot coolant ejection. This configuration was designated as cast cutback configuration. The third is the pressure surface ejection via discrete film cooling holes within a step cutback. This configuration was designated the machined cutback configuration. The above configurations were incorporated into three flat plates manufactured using stereolithography. In the aerodynamic study, the static pressure distribution and discharge coefficient for the three configurations were compared. Furthermore, two dimensional total pressure measurements were carried out using a traverse mechanism downstream of the test plates. The total pressure measurements were used to compute the mixed out losses for the three configurations. It was found that the datum and machined cutback configurations have similar discharge coefficients and mixed out losses whilst the cast cutback configuration produces greater mixed out loss. The film effectiveness and heat transfer coefficient on the pressure surface downstream of the coolant ejection was obtained using a steady state heat transfer technique. The effectiveness measurements were compared with those from the literature and correlated against the two dimensional slot model. The heat transfer measurements show that the cast cutback configuration has the potential to give higher effectiveness at the trailing edge.

Film cooling is vital for the cooling of the blades and vanes in the high temperature environment of a jet engine high pressure turbine stage. Previous research into film cooling has typically concentrated on its time-mean performance. However, results from other studies upon more simplified geometries, suggest that coherent unsteadiness is likely to also be present in film cooling flows. The research presented in this thesis, therefore, aims to characterise what coherent unsteadiness, if any, is present within film cooling flows. Cylindrical and shaped cooling holes, located upon the pressure surface of a turbine blade within a large scale linear cascade, have been investigated. A blowing ratio range of 0.5 to 2.0 has been investigated, with either a plenum or perpendicular crossflow at the cooling hole inlet. Particle Image Velocimetry, high speed photography and Hot Wire Anemometry have been used to investigate the jet downstream of both cooling holes. The impact of crossflow at the hole inlet upon the flowfield inside both cooling holes has been investigated using Hot Wire Anemometry and a further numerical model solved by applying TBLOCK. The results presented in the current thesis, show the existence of two coherent unsteady structures in the jet downstream of both the cylindrical and the shaped holes. These structures are called shear layer vortices and hairpin vortices, and their formation is dependent on the velocity difference across the jet shear layer. Inside the cooling hole coherent hairpin vortices also appear to occur, with their formation dependent on the direction and magnitude of the crossflow at the hole inlet. The coherent unsteadiness presented here is shown for the first time for film cooling flows, and recommendations to build on the current study, in what is potentially an interesting research area, are made at the end of this thesis.

Improvements upon current gas turbine sealing technology performance are essential for decreasing specific fuel consumption to meet stringent future efficiency targets. The clearances between rotating and static components of a gas turbine, which need to be sealed, vary over a flight cycle. Hence, a seal which can passively maintain an optimum clearance, whilst preventing contact between itself and the rotor, is extremely desirable. Various configurations of a Rolls Royce (RR) seal concept, the Large Axial Movement Face Seal (LAMFS), use static pressure forces to locate face seals. Prototypes were tested experimentally at the Osney Thermofluids Laboratory, Oxford. Firstly a proof-of concept rig (simulating a 2-D seal cross-section) manufactured by RR was re-commissioned. The simplest configuration using parallel seal faces induced an unstable seal housing behaviour. The author used this result, CFD, and analytical methods to improve the design and provide a self-centring ability. A fully annular test rig of this new seal concept was then manufactured to simulate a 3D engine representative seal. The full annulus eliminated leakage paths unavoidable in the simpler rig. A parametric program of experiments was designed to identify geometries and conditions which favoured best-practice design. The new seal design is in the process of being patented by Rolls Royce. A 'fluidic' seal was also investigated, showing very promising results. A test rig was manufactured so that a row of jets could be directed across a leakage cross-flow. An experimental program identified parameters which could achieve a combined lower leakage mass flow rate compared with the original leakage. Influence of jet spanwise spacing, injection angle, jet to mainstream pressure ratio, mainstream pressure difference and channel height were analysed. It is hoped this thesis can be used as a tool to further improve these seal concepts from the parametric trends which were identified experimentally.

Maintenance and diagnostics play a vital role in the aviation sector. This is especially true for the engines, being one of the most vital components. Lack of maintenance, or poor knowledge of the current health status of the engines, may lead to unforeseen disruptions and possibly catastrophic effects. To keep track of the health status, and thereby supporting maintenance planning, model based diagnostics is a key factor.  In the work going into this thesis, various aspects of model based gas turbine diagnostics, focused on aero engines, are covered. First, the importance of knowing what health parameters may be derived from a set of measurements is addressed. The selected combination is herein denoted as a matching scheme. A framework is proposed where the most suitable matching scheme is selected for a numerically robust diagnostic system. If a sensor malfunction is detected, the system automatically adapts. The second subject is a system for detecting a burn-through of an afterburner inner liner. This kind of burn-through event has a very small impact on available on-board measurements, making it difficult to detect numerically. A method is proposed performing back-to-back testing after each engine start. The method has shown potential to detect major burn-through events under the preconditions, regarding data collection time and frequency. Increasing these will allow for more accurate estimations. The third subject covers the importance of knowing the airplane installation effects. These are generally the intake pressure recovery, bleed and shaft power extraction. Just like inaccurate measurements affect diagnostic results, so does erroneous installation effects. A method for estimating said effects in the presence of gradual degradation has been proposed by using neural networks. By retraining the networks throughout the degradation process, the estimation errors is reduced, ensuring relevant estimations even at severe degradations. Finally, an issue related to the general lack of on-board measurements for diagnostics is addressed. Due to lack of measurements, the diagnostic model tend to be underdetermined. A least square solver working without a priori information has been implemented and evaluated. Results from the solver is very much dependent on available instrumentation. In well instrumented components, such as the compressors, good diagnostic accuracy was achieved while the turbine health estimations suffer from smeared out results due to poor instrumentation.

Predictive models of structures containing frictional joints presently suffer from poor descriptions of interface behaviour at the joints. This thesis aims to address this shortfall by furthering the physical understanding of parameters affecting interface behaviour such as friction and contact stiffness. Aspects of friction and contact stiffness relevant to the characterisation of fretting joints are investigated by a combined modelling and experimental approach. Friction and wear behaviour in gross-slip fretting are investigated by in-line and rotational fretting tests. New 3D topography parameters are found to be useful in the analysis of surfaces during fretting. Wear-scar shape is found to be dependent on material. A phenomenon whereby friction increases during the gross-slip phase of individual cycles is found to be due to wear-scar interaction primarily through the interference of local features distributed over the contact area. These features are similar in size to the applied fretting stroke. A simple model to explain the behaviour is put forward which shows that wear-scar shape determines the form of the friction variation. A finite-element (FE) model of the interaction of an elastic-plastic asperity junction is used to predict sliding friction coefficients. The modelling differs from previous work by: permitting greater asperity overlaps, enforcing an interface shear strength, and allowing material failure. The results are also used to predict friction coefficients for a stochastic rough surface. The magnitudes of the predicted friction coefficients are generally representative of experimental measurements. Results suggest that friction arises from both plasticity and tangential interface adhesion. Contact stiffness is studied for both fretting and non-fretting. A technique to isolate the true interface stiffness from results derived from load-deflection data is developed by comparing experimental and FE results. In the fretting wear case, comparison of tangential contact stiffness results in the literature with FE results reveals an interface whose compliance dominates the response to the extent that stiffness is proportional to contact area. In fretting tests such as this, wear debris is thought to be a factor contributing to high interface compliance. Non-fretting experiments performed here show that, at higher pressures, interface domination is reduced as the contact approaches the smooth case. Experiments are performed where contact stiffness is measured simultaneously by both ultrasound and digital image correlation. The effect of normal and tangential loading upon the contact stiffness (normal and tangential) is investigated. Experimental evidence showing that ultrasound measures an ‘unloading’ stiffness while DIC measures a ‘loading’ stiffness is obtained for the case of tangential loading where the ‘DIC stiffness’ decreases with increasing tangential load whereas the ‘ultrasound stiffness’ remains approximately constant. On average, ultrasound gives magnitudes 3.5 and 2.5 times stiffer than the DIC results for the normal and tangential stiffness cases, respectively. The difference in magnitudes can largely be physically explained, and is relatively small considering the significant differences between the techniques. Therefore, both methods can claim to give valid measurements of contact stiffness – though each has its own limitations which are outlined herein.

The core aim of this research project was to improve understanding of the effects of microstructure and crystallographic texture on the high strain rate plastic deformation behaviour of the industrially important Titanium alloy, Ti-6Al-4V. To facilitate this study, four rolled plates of Ti-6Al-4V, with varying thermo-mechanical processing histories, were provided by TIMET Corp., the world’s largest supplier of Titanium product. To determine the nature of each plate’s microstructure and the crystallographic texture of the dominant α phase, the four Ti-6Al-4V plates were microstructurally characterised using techniques such as optical microscopy and electron backscatter diffraction (EBSD). To determine the effects of the measured microstructures and textures on the strain rate dependent plastic deformation behaviour of the four Ti-6Al-4V plates, uniaxial compression and tension tests were carried out in the three orthogonal material orientations at quasi-static (10^-3 s^-1) and high strain rates (10^3 s^-1) using a standard electro-mechanical test device and split-Hopkinson pressure bars (SHPB), respectively. To provide further understanding of the effects of microstructure and texture on the plastic deformation behaviour of Ti-6Al-4V, this time under complex impact loading conditions, the classic Taylor impact experiment was adapted to include an optical measurement and geometry reconstruction technique. A novel experimental setup was designed that consists of an ultra-high speed camera and mirror arrangement, allowing the Taylor impact specimen to be viewed from multiple angles during the experiment. Using the previously mentioned optical measurement and geometry reconstruction technique, it was then possible to gain valuable, previously unobtainable, data on the deformation history of Taylor impact specimens in-situ, such as the major/minor axes of the anisotropically deforming elliptical specimen cross-sections as a function of time and axial position, true strain as a function of time and axial position, and the true strain rate as a function of axial position. The technique was verified by testing a specimen cut from the in-plane material orientation of a clock-rolled high purity Zirconium plate. The output measurements from a post-deformation image frame were compared with measurements of the recovered specimen made using a coordinate measurement machine (CMM), with analysis showing excellent agreement between the two techniques. The experiment was then carried out on specimens cut from the two orthogonal in-plane material orientations of one of the four Ti-6Al-4V plates. Analysis of the data from these experiments gave significant insight into the plastic deformation behaviour of macroscopically textured Ti-6Al-4V under complex impact loading. Recovered Ti-6Al-4V specimens from the outlined Taylor impact experiments were then sectioned along specific planes and microstructurally characterised using EBSD, with comparisons made between the pre and post-deformation microstructures. From this analysis, and the previously discussed geometry reconstruction technique, insight was gained into the effects of micro-texture on the general anisotropic plastic deformation behaviour of Ti-6Al- 4V plate materials and in particular the role of micro-texture on the formation of deformation twins. Finally, the understanding gained from these experiments, and a detailed review of the literature, was used to inform a novel, physically based material modelling framework, capable of capturing the effects of microstructure and texture on the strain rate and temperature dependent plastic deformation behaviour of Ti-6Al-4V. The model was implemented in the computational software package, MATLAB, and verified by comparison with the mechanical characterisation results from one of the Ti-6Al-4V plates. A number of frameworks are discussed for implementing the new Ti-6Al-4V model within finite element (FE) analysis software packages, such as ABAQUS, LS-DYNA and DEFORM. It is hoped that the new Ti-6Al-4V model can be used to optimise the design of Ti-6Al-4V components and structures for impact loading scenarios.

The primary aim of this research was to develop and improve the experimental method and data interpretation for strain measurements using diffraction methods to gain a better understanding of micromechanical deformation and anisotropy of lattice strain response. Substantial part of the research was devoted to the development of the laboratory high energy X-ray diffractometer (HEXameter) for bulk residual strain evaluation. White beam energy dispersive X-ray diffraction was chosen as the principal diffraction mode due to its extreme efficiency in utilising X-ray flux and its ability to capture large segments of diffraction patterns. The specimens that have been examined were real engineering components, mechanically deformed specimens and thermally treated specimens, ranging from dynamic in-situ measurements to ex-situ materials engineering. For the real engineering components, a wedge coupon from the trailing edge of a Ti64 wide fan blade and a turbine combustion casing were examined. Among the mechanically deformed specimens that have been measured were shot-peened steel plates, elasto-plastically bent bars of Mg alloy and cold expanded Al disks. Amongst the thermally deformed specimens, laser-formed steel plates, thermal spray coatings, a manual inert gas weld of Al plates, a friction stir weld of Al plates and Ni tubes and a quenched Ni superalloy cylinder used for strain tomography were studied. In-situ loading experiments have also been carried out, such as experiments on pointwise mapping of grain orientation and strain using the 3DXRD microscope at the ESRF and in-situ loading experiments on titanium alloy, rheo-diecast and high pressure diecast Mg alloy, IN718 Ni-base superalloy and Al2024 aluminium alloy. Experimental results from X-Ray diffraction and strain tomography were used to achieve a better understanding of the material properties. Some results were compared with polycrystal Finite Element model predictions. Amongst the most prominent research achievements are the development on the HEXameter laboratory instrument, including: (i) the development of special collimation systems for the detectors and the source tube; (ii) the development of a twin-detector setup (that allows for simultaneous determination of strain in two mutually orthogonal directions); (iii) improved alignment procedures for better performance; and (iv) the adaptation of instrumentation for efficient scanning of both large and small components, that included choosing and adapting translation devices, programming of the translation system and designing sample mounting procedures. In this research several approaches to data treatment were investigated. Quantitative phase analysis, single peak fitting (using custom Matlab routines and GSAS) and full pattern fitting (with individual pattern data refined by GSAS and batch refinement done by invoking GSAS via a Matlab routine) were applied. Different Matlab routines were written for specific experimental setups; and various analysis methods were selected and used for refinement depending on the requirements of the measurement results interpretation. 16 papers were published, ensuring that the results of this thesis are readily available to other researchers in the field.

Environmental issues such as climate change are leading to important sustainability challenges in the aerospace industry. Composites are light materials that are extensively used to replace metals and reduce the aircraft weight, the goal being to decrease the fuel consumption in flight and limit the emission of greenhouse gases. However, these high performance materials are associated with a complex supply chain including energy-consuming processes. Most of the decommissioned composite products are currently landfilled and nothing proves that the weight reduction allowed by these materials compensates those negative aspects. The purpose of this master thesis is to determine if the introduction of composites in aero-engines can be sustainable and how it can be achieved. To do so, three polymer-matrix composite components from GKN Aerospace have been studied and compared with their metallic baseline from environmental, social and economic perspectives. Several options for materials selection, manufacturing processes and recycling possibilities have been investigated in the same way. The assessment on GKN Aerospace’s components showed that the weight savings provided by composites have a strong and positive influence on their sustainability. Component B shows the best results: with 16% of weight savings with composites versus the titanium baseline, it appears clearly that the composite version is the most sustainable one. Component A2 composite version also provides interesting weight savings (14%) but has an aluminum baseline, which makes the composite component more sustainable in some aspects but not all of them, especially economically speaking. Finally, for component A1, the composite version, which does not provide weight savings, is more economically feasible, but quite tight with the titanium baseline on environmental and social aspects. Therefore, it appears that composite components are more likely to be sustainable if they provide significant weight reduction and if the baseline is titanium. A few strategies would merit attention to make future composite components more sustainable. On the one hand, using thermoplastic composites have potential to reduce the environmental, social and economic impact. In fact, these materials can be fully recycled and reused, present less risks to handle and can be produced for a lower cost. Nevertheless, the knowledge on these materials is more limited than on thermoset composite and the implementation of such a solution will take time. On the second hand, introducing composite recycling processes in the products lifecycle can increase a lot the sustainability of composite components. The manufacturing scrap and the decommissioned products can both be recycled in order to reduce the environmental impact and generate benefits by re-using or selling the recycled material.