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In many industrial gas turbine combustors the injection of liquid fuel resembles the simple configuration of a jet in a rectangular channel with cross-flowing air, albeit with complex geometry both upstream and downstream from the channel. Therefore the detailed study of a jet in cross flow is an appropriate platform for the development of models for atomization and vaporization, both of which are key processes influencing efficiency and the emissions of pollutants from practical combustion devices. In the current study the breakup of a liquid jet and vaporization of droplets are modelled using an entirely Eulerian approach, where the liquid phase is treated analogously to a gas species in a multi-component reacting mixture. A novel boundary condition is proposed for the liquid surface area per unit mass at the jet inlet, and results are found to be insensitive to adjustments of the size parameter for this boundary condition. Validation is carried out in two stages: firstly turbulence closure via the Reynolds Averaged Navier-Stokes (RANS) approach with the standard constants is assessed for a gas-phase jet in cross flow with two different software packages; then predictions of the Sauter mean diameter of droplets are compared to measurements of a liquid jet in cross flow at 6 bar pressure. The turbulence model yields a reasonably accurate prediction of the flow field provided that the distribution of velocity across the jet inlet is specified. Droplet sizes agree well with the experiment except for a small region near the floor of the channel, where discrepancies can be attributed to the RANS closure. Application of the model is demonstrated for an industrial gas turbine combustor at its full load operating condition.

This thesis describes in details the experimental and numerical investigations conducted to determine the filling and flow behaviour inside dynamic operating piston cooling galleries. An experimental test rig was built to replicate the reciprocating motion of internal combus- tion engine pistons to allow for varying engine speed, stroke length, oil flow rate and piston size. Two transparent models were produced, representing cooling galleries for small sized engine pistons found in passenger vehicles and large sized engine pistons found in heavy goods vehicles and earth moving equipment. High speed image processing was undertake to capture the flow behaviour inside the galleries during the piston cycle. An oil mixture was used to replicate the properties of engine oil at engine operating conditions. The flow inside the gallery was recorded from various view positions to capture the flow throughout the gallery. The flow domains representing the investigated gallery shapes were generated and computational fluid dynamic (CFD) studies of the two-phase flow behaviour were performed. The studies of gallery filling and in-gallery flow behaviour were undertaken for the same parametric conditions as defined in the experiments. The flow behaviour and filling of both studies, experimental and numerical, are compared and discussed. The results of the experimental and numerical studies compared well in terms of the identified directions of the main bulk oil flow within the small and large gallery and for the investigated crank speed and flow rate conditions. Both galleries showed that the flow in the gallery from inlet to outlet was mainly driven by the oil jet entering the gallery. The continuous entering jet forced a flow of the oil into the gallery branches. Strong turbulence in the direct vicinity of the inlet occurred as air and oil mixing was significant. It was found that the size of the turbulence region depended on the flow rate and engine speed, as well as the direction of movement of the gallery. It also sustained the presence of a large amount of medium-sized air bubbles due to mixing effects. Although the CFD did not predict the fine detail of the turbulent mixing, it did capture the underlying main flow characteristics, including short circuiting at the inlet. In the mid-gallery section the formation of large air bubbles took place, which could span across the gallery height. The flow behaviour was still driven by the inflow, but also controlled by the gallery cross-sectional shape. At the gallery outlet the flow was predominantly inertia driven as a result of the gallery movement with the oil exiting mainly during the upward stroke, allowing formation of large air bubbles. Distinctly different flows were encountered within the large and small gallery. The large gallery volume showed more unstructured or chaotic flow behaviour, especially in the mid- gallery section, as a result of the complex cross-sectional shape. In the small gallery volume the bulk flow was more controlled and wall-guided due to the limited space and regular cross-sectional shape. It was also found that the overall gallery filling for both galleries varied only by approximately 2% during the crank cycle. In contrast the variation of gallery section fillings of up to 30% and 50% for the large and small gallery respectively were determined, highlighting the effects of air movement within the galleries. The experimental results showed that an increase in flow rate, reflected by an increase in jet exit velocity, led to strong air entrainment of micro-scale bubbles into the oil clearly visible inside the gallery, while an increase in engine speed led to significantly lower formation of micro-scale air bubbles in the gallery. In contrast the CFD struggled to capture such fine details, unless the mesh density reached a very fine level, resulting in unsustainably long simulation times.

The thesis describes a programme of research to determine ignition energy requirements in flowing kerosene spray air mixtures under various flow conditions such as velocity, mixture strength, spray mean drop size and drop distribution. In order to determine the spray characteristics of mixture ratio, mean drop size and drop distribution in the flowing fuel-air spray accurately, new designs have been evolved and employed. A single rectangular pulse of constant power was employed for initiating ignition in the mixture. The flow parameters were found to have considerable influence on spark characteristics and hence on the energy released in the spark. The breakdown voltage requirements of the spark in the two phase flow differed from they of premixed gaseous mixtures. In the range of weak mixtures investigated, optimum spark duration was found to vary depending on spray drop size between 30 and 60 microseconds. Minimum ignition energy increased with increase in velocity, but decreased with reduction in drop diameter and with increase in equivalence ratio. Low flow number atomisers giving small drop sizes extended the weak ignition limits for a given spark energy. Spray drop size and distribution were found to have a singularly large influence on all aspects of ignition. The thesis includes a detailed account of the designs and procedures employed in carrying out the investigation, and also a discussion on the significance of the results on the practical aspects of liquid fuel ignition in aero engine combustion system.

In conventional gas turbine performance methods, components are represented by characteristics where the 3d properties of the flow fields' are averaged providing key flow properties at component interfaces. For the design of a component, the consideration of the 3d nature of the flow is crucial and Computational Fluid Dynamics (CFD) is well established in the design process; however computational challenges generally limit the application to individual components only. The fact that each engine component has an effect on the overall engine performance sets a strong incentive to link the two methods closer together. This thesis explores the potential benefits of the 'coordinated application of performance modelling and CFD through two proof-of-concept case studies. The, research context of the first case study was high fidelity performance simulation. A performance simulation process With a 2d radial representation of the low pressure system has been developed for a high bypass turbofan. The intake and bypass section were represented using axial-symmetric 2d CFD modules and radial flow profiles were exchanged at the component interfaces to an existing 2d radial fan model. The iteration procedure between the two tools was performed manually and investigated for various operating conditions. A match of the flow data between the tools was achieved for the intake. Guidance for improvements and an automation of the process are also given. The research of the second case study involved the design of component subsystems in an industrial application and illustrates the potential of using CFD and performance simulation for the design of a compressor washing system; The optimisation of a compressor washing system for an industrial gas turbine has been studied using a 3d CFD model of the intake component. Due to the interaction of droplets with the surrounding air flow, the key factors from injection system and' the air flow demand of the gas turbine were investigated. Boundary conditions were provided using a performance simulation tool which facilitated the evaluation of relevant operating conditions. Associated spray parameters were derived from numerical sensitivity studies calibrated to data from visual field inspections and key design parameters were provided. Improvements were suggested and confirmed for a similar field installation.

Due to the ever-increasing global drivers focused on increasing fuel economy in tandem with decreasing the environmental impact of automobile usage; the automotive sector is rapidly embracing widespread use of Diamond-Like Carbon (DLC) coatings. DLC coatings have the potential to reduce the required level of many traditional oil additives that can negatively impact on both the environment and certain parts of the car engine, specifically the catalytic converter. Furthermore DLC shows promise with regards to reducing friction and can be highly efficacious at reducing wear. The field of research into DLC is ever-developing and many examples of doped DLCs exist. Currently, there is no firm consensus on which dopants are best to include in the DLC matrix when it is being employed within the automotive field. Adding to this the lack of a sufficient understanding of how current engine oil additives interact with DLC; the motivation for undertaking an in-depth analysis of both a-C:H and Si-DLC with current engine oils is clear. This thesis addresses these issues and presents evidence on how both Si-DLCs and a-C:H DLCs interact with current engine oil additives to reduce wear in the engine. The fundamental tribochemistry governing DLC’s interactions at the interfaces are explored with specific reference to wearing of Si-DLCs. Tribological experiments are undertaken to emulate certain conditions within an engine using both reciprocating pin-on-plate tribometers and pin-on-disc tribometers. A novel Si-DLC is created and tested to explore the effect of tri-doping on the coating. Advanced surface analysis techniques are used to gain a full understanding of what processes have taken place at the interfaces. This includes use of X-ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry and scanning light interferometry. Key findings include the effect that Si doping has on the DLC coating with regards to structure, friction and wear. The fundamental observation that the Si-DLCs examined consistently exhibited wear at higher rates when compared to the a-C:H.

The thesis reports experimental and theoretical studies of premixed combustion rates at high pressure and temperature. It focuses on measurements of laminar and turbulent burning velocities at high pressures and temperatures approaching those in engines, with emphasis on flame instabilities. To encourage the development of such instabilities, mixtures with negative Markstein numbers were employed. Three different methods were used to measure burning velocities in a spherical bomb. The bomb was fitted with windows for observing flame propagation at the centre of the bomb and a transducer to measure pressure. Four fans at the wall of the bomb were employed for mixing and the generation of turbulence. The first two methods of measuring burning velocities were well established and involved central ignition. The third method was new and involved implosions of two flame kernels that originated at spark plugs mounted near the wall. It enabled the later stages of burning at the high pressures to be observed and burning velocities to be measured. The first method depended on highspeed schlieren photographic measurements of the flame speed, dr / dt , at different radii,r, supplemented by pressure measurements. The second method was employed when the flame front has propagated beyond the boundaries of the window and could no longer be observed. The expression for the burning velocity rested upon the assumption that the flame was spherical and the fractional pressure rise was equal to the fractional mass burned. Two different approaches were employed for the new third method, one was based on geometrical considerations, the other on the fractional pressure rise. A knowledge of the flame area and the appropriate geometrical analysis enabled two expressions to be obtained for the burning velocity. The agreement between the two different approaches for obtaining burning velocities, and the general consistency of the results for both initially laminar and turbulent flames, showed the technique to be accurate and suitable for obtaining burning velocities at high pressure. As a result, burning velocities, initially laminar, were measured for iso-octane - air at equivalence ratios ranging from 0.8 to 1.6 at initial pressures of 0.5 and 1.0 MPa. They were also measured for hydrogen - air mixtures at equivalence ratios of 0.3 to 0.5. Modification of the linear theory of flame instability of Bechtold and Matalon enabled the laminar burning velocity to be obtained from the values of unstable burning velocities. Enhancements of the laminar burning velocity of up to six fold were measured. Turbulent burning velocities were measured over a range of rms turbulent velocities ranging from 0.25 to 3 mls. It was found that these values of burning velocity were higher than those predicted from earlier expressions, derived predominantly from more stable flames close to atmospheric pressure. The possibility that turbulent burning velocities might be enhanced, not only by the effect of flame stretch at negative Markstein numbers, but also by flamelet instabilities was also investigated at high pressures and with mixtures with very low Markstein numbers. Stoichiometric and rich iso-octane-air flames were selected for this study and mixtures were ignited at initial pressures of 0.5 and 1.0 MPa. This enabled burning velocities to be measured up to 6 MPa.

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