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This thesis first provided strategic recommendations for the research sponsor, Rolls- Royce plc (RR) and then applied optical diagnostics to measure aero gas turbine fuel spray properties in order to predict Oxides of Nitrogen (NOx) emissions and combustion instability. Analysis of the large civil aero engine sector suggested possible courses of action for RR to protect itself from short-term market volatilities and also prepare for three long term changes in strategic operating context: air traffic growth; tighter United Nations enforced aero engine combustion emissions legislation and entry of civil aviation into the European Union Emissions Trading Scheme. A collaborative game theoretic approach was explored during the pre-competitive, pre-technology, capability acquisition aero engine design phase on unproven future technologies to reduce R&D expenditures, development times and the costs of failure. Lean Prevapourised Premixed combustion demands excellent spray atomisation quality to sustain combustion efficiency, stability and to minimise pollutants. Post development of an improved procedure to calibrate laser signals, methodology to predict NOx and technique to optimise rig operating conditions that minimised fractional discrepancies in two-phase flow behaviour with corresponding engine conditions, this thesis applied quantitative Planar Laser Induced Fluorescence (PLIF) and Laser Sheet Dropsizing (LSD) to measure the fuel placement and dropsize distribution in the near nozzle regions of RR liquid-fuelled hybrid, airblast and pressure-swirl sprays. Measurements were made under non-combusting, low pressure conditions and results were processed to identify fuel injector designs that exhibited low emissions and high stability for the Affordable Near Term Low Emissions (ANTLE) and Instability Control of Low Emission Aero-Engine Combustors (ICLEAC) engine demonstrator programmes. Results also provided validation data and boundary conditions for spray computational codes. Research findings will improve RR core competencies in fuel injection research to accelerate the development and deployment of low emissions aero engine technology.

A swirl stabilised dump combustor capable of imposing flow perturbations creating combustion instabilities has been designed and commissioned. The capability of supplying different fuel mixtures (methane hydrogen blends) has been incorporated. Additional capability is the facility to preheat the combustion air prior to chamber entry and to be able to introduce dilution air into the chamber. The chamber itself is of fused silica quartz to allow non-intrusive optical diagnostics. High speed CH* Chemiluminescence has been performed to qualitative characterise the unstable heat release rate of pure methane and methane hydrogen blended flames to allow analysis of the mean deconvoluted flame structure. High speed Stereoscopic Particle Imaging Velocimetry (SPIV) has been used to acquire the flow field throughout the chamber and focusing upon the Annulus entry. These diagnostics have been phase locked to the imposed perturbation. A selection of conditions is presented with three different perturbation frequencies within the low frequency range. These reveal vastly different reacting and flow field structures. The difference of structures is attributed to behaviour of the IRZ (Internal Recirculation Zone) and CRZ (Corner Recirculation Zone) in altering the flame shape. All conditions exhibited the axisymmetric/bubble vortex breakdown mechanism responsible for stabilisation. Both single cell and double cell structures were observed in the mean flow field vector maps. The mechanism of oscillating heat release rate is attributed to oscillations of flame surface area. Profiles of integrated heat release rate and flame exhibit the same profile shape and behaviour correlating very well. The inclusion of hydrogen had no quantifiable impact upon the mean reacting or flow field structures using the current diagnostics. Investigation into the nature of the turbulence of the shear layers close to the annulus is presented for three perturbation frequencies. This highlighted periodic structures within the turbulence corresponding to the imposed perturbation frequency. It was found that excitation of both shear layers for all turbulent components was not always true and depended upon the perturbation frequency and flow structure close to the annulus. Two oppositely rotating vorticity structures were revealed attached to the outer and inner circumference of the annulus. These structures protruded into the chamber and spread radially. Frequency analysis of these two structures revealed both were oscillating at the perturbation frequency indicating vorticity shedding. The mean vorticity structures are shown to be influenced also by the behaviour of the recirculation zones.

A new technique to simultaneously and instantaneously resolve 3D velocity/2D strain rate fields and scalar/scalar gradient fields was developed and evaluated in this study. This technique combines Planar Laser Induced Fluorescence of the NO radical (NO-PLIF) and Stereoscopic Particle Image Velocimetry (SPIV). It was found that the NO-PLIF technique allowed the determination of various iso-c contours and as such would, in principle, allow the study of the influence of the heat release on various properties, provided a calibration of the NO-PLIF signal as a function of temperature is achieved. It was also shown that the NO-PLIF technique may not be unambiguous at detecting flame extinction. The SPIV technique allowed the determination of the velocities in 3D and of the strain rates in 2D from which the most extensive and the most compressive strain rates but not the intermediate strain rate could be extracted. Information on strain rates and progress variable gradients were of particular interest in this study as they were needed to study the turbulence-scalar interaction which appears explicitly in the transport equation for the scalar dissipation rate which was derived recently. Using the technique above mentioned, this work also aimed at gathering and analysing data such as flame normal orientation, progress variable gradients, velocity change across the flame front and strain rates along the flame contours in turbulent premixed hydrogen/air flames with added nitrogen. The flame normal orientation was found to be consistent with the regime of the flames studied. A new method was designed and presented to infer from the progress variable gradients the component of the flame normal in the third dimension. The velocity change across the flame front, inferred from the SPIV data, was found to be extremely small. It is thought that the (low) heat release of the flames studied contributed more to corrugation of the flame front than acceleration of the gases across the flame front. The strain rates were studied along apparently non-wrinkled and clearly wrinkled flame contours. Their variation could not successfully be linked to curvature solely. Their values were mostly below the value expected for extinction strain rates. Last, this study aimed at investigating the turbulence-scalar interactions in turbulent premixed hydrogen/air flames with added nitrogen via the characteristics of the alignment of the flame normal vectors with the principal strain rates. The results of this study are quite different from earlier experimental results obtained for turbulent premixed ethylene/air flames. The strong preferential alignment of the flame front normal with the most extensive strain rate observed for ethylene/air flames could not be observed for the hydrogen/air flames with added nitrogen studied in the present work. The key outcome of this study was that no preferential alignment could be observed for most of the flames. A slight preferential alignment of the flame front normal with the most compressive strain rate was observed for the flames with very low adiabatic flame temperature. The differences observed were attributed partly to Lewis number effects and partly to the low heat release superimposed on the hydrodynamic fields in the flames studied.

Summary Integrated gasification combined cycle (IGCC) systems, which utilize coal, petroleum coke, heavy oil, biomass and waste materials as a feedstock, continue to enter the power generation market. The gasification products from gasifiers using these feedstocks are mixtures of hydrogen, carbon monoxide and inerts like nitrogen, carbon dioxide and water. These mixtures are then used as a fuel in low-emission power generation applications. Unlike natural gas or methane, which has been widely used and researched for many years, these mixtures have not been widely investigated. Thus the aim of this study is to provide data on the combustion properties of syngas mixtures, mainly focusing on laminar burning velocities and critical strain rates to extinction. These combustion properties data are essential for gas turbine combustor modelling using turbulent burning velocity closure models. The establishment of such a database in this study mainly relies on numerical computations. Therefore, the experimental campaign was limited to investigation of several CO/H2/N2 fuel mixtures fuel mixtures at different equivalence ratios and operating conditions. The laminar burning velocity values, obtained from the experimental campaign were used mainly for validation of the chemical kinetics model and reaction mechanism. The principal outcome from this study is that at ambient conditions and reactant preheat temperatures up to 400K experimental laminar burning velocity values compare well with numerical predictions. The laminar burning velocity tests at high pressure presented a number of complications due to the formation of cellular flames and the flow in theburner tube entering the transitional laminar to turbulent regime. As a result the numerical model could not be fully validated experimentally for high pressure conditions. A comprehensive combustion properties database has been created using numerical simulations, based on comprehensive descriptions of the chemical kinetics and extensions using neural networks. CFD simulations of reacting flows in a practical combustor geometry demonstrated the importance of obtaining accurate laminar burning velocities and critical strain rates to extinction data.

The main objective of this work is to create a robust model for two-phase liquid spray combustion flow using vegetable oils, to investigate the flow structure generated by a swirler array with different fuels, and secondly to assess and optimise the capability of the CFD to predict accurately the results obtained experimentally and eventually enhance CFD model development and simulation. Validation is achieved by comparing the numerical results obtained with CFD with the experimental measurements. The purpose of this research is to increase the scientific understanding of the fundamental mechanisms of the spray combustion process using a carbon neutral fuel such as ethanol and biodiesel. In fact, very few numerical simulations of liquid biomass fuels in gas turbine systems are available in the literature. The flames are simulated using the commercial code FLUENT. The combustion/turbulence interaction is modelled using the laminar flamelet approach with detailed chemistry modelled using the OPPDIFF model from CHEMKIN. While the experiments could be carried out only up to 3 atm, the simulations were further extended to a maximum pressure of 10 atm. The FLUENT results were assessed qualitatively and quantitatively between the experimental measurements and the simulation. The cold flow features have been captured by the present simulations with a good degree of accuracy. Effect of air preheating was investigated for the biodiesel, and sensitivity to droplet size and spray angles variation were analysed. Good agreement was obtained for ethanol except in the fuel lean region due to failure of the FLUENT laminar flamelet model to capture local flame extinction while biodiesel simulation resulted in a significant overprediction of the flame temperature especially in the downstream region and satisfactory results further upstream. The results show the importance of setting proper droplet initial conditions, since it will significantly affect the structure of the flame.

Three novel multicomponent fuel spray droplet evaporation models are developed by employing the theory of continuous thermodynamics(CT) with the aim of applying them in the design and analysis of various energy conversion devices such as, aircraft jet engines, liquid-fuel rocket engines, diesel engines, and industrial furnaces. The CT methodology seeks to represent complex mixtures - for example,aviation kerosene or JP8 that typically comprise blends of a large number of chemical compounds by using probability distribution functions (PDFs). The components of JP8, which is constituted by the homologous series of paraffin, naphthene, and aromatic hydrocarbons; are each represented by the Pearson-Shultz type three-parameter gamma PDF, where the three (shape, scale, and origin) parameters characterise changes in the mixture composition. The phase transition of the liquid droplet due to evaporation is modelled using both low-pressure (LP) and high-pressure (HP) vapour-liquid equilibrium (VLE) models employing various mixing and combining rules by applying a general cubic equation of state (CEOS). Interestingly enough, the phase transition of the liquid fuel into vapour mixture is characterised by a change in the PDF scale parameter alone. Once the description of the fuel mixture is complete, the traditional species and energy transport equations both for the liquid and vapour phases respectively, are re-written using the composition PDF moments under Lagrangian and Eulerian frameworks. In order to solve the governing equations for the three droplet evaporation models, which characteristically involve phase change and a moving interface, a novel fully Adaptive Method Of Lines using B-Spline Collocation (AMOLBSC) is developed. The models are tested at various pressures, temperatures and convective conditions, including at a lean, premixed, prevaporised (LPP) combustor operating condition. In general, the computational results at an ambient pressure close to atmospheric showed good to excellent agreement against available experimental data in the literature. However, for ambient conditions with elevated-high pressures and temperatures only models that employ the HP formulation gave reliable results. In particular, when the liquid is at or near its critical pressure and temperature it is characterised by faster vaporisation and shorter droplet lifetime, including some evidence of liquid mass diffusion. The liquid model that incorporates the effects of liquid core circulation using semiempirical approximation and adaptive mesh refinement (AMR) technique is the most accurate and computationally efficient, although further work is required to establish its ranges of applicability.

The latter half of the 20th century has seen great strides made in understanding premixed combustion, and this combined with advances in computing, has lead to significantly improved combustion models. Over the same period changes in the international energy market, allied with major technological advances, have promoted gas turbines to the forefront of power generation. Lean premixed combustion is key to the low emissions produced in such devices, but with ever more stringent emissions regulations burner design becomes increasingly vital. However there has, perhaps, been a lack of emphasis on research areas that directly influence practical burner design. In particular it is possible to identify high pressure combustion and the development of models that address the pragmatic requirements of industry as areas that have received insufficient attention. This study aims to examine the effectiveness, at elevated pressure, of two models that appear to better meet the demands of industry. The selected models are the turbulent flame speed closure and fractal models. These are implemented in a novel partially premixed form within the CFD research code SOFIE. Comparisons are made between measurements, made by applying particle image velocimetry in a novel manner, and predictions in order to determine the accuracy of these models. The principal conclusion was that although the turbulent flame speed closure model replicated the experimental measurements surprisingly well the fractal model did not. However, a major weakness was identified in extending premixed combustion models, based on the concept of a progress variable, to partially premixed problems. This weakness introduced significant errors into prediction of the fuel distribution, which at the extreme could lead to the apparent 'creation' of fuel. No simple solution to this problem is immediately apparent, and hence it is argued alternative approaches, based on the techniques used in diffusion flames, should be investigated.

This study describes the simulation and experimental investigation of a heptane pool fire, burning within a small compartment, in which interaction between a number of key physical processes is amplified. In particular, the configuration emphasises the coupling of buoyancy induced ventilation, smoke production and radiation heat transfer to the liquid fuel surface, from the luminous flame zone, from the smoke filled ceiling layer and from the confining walls. This study contrasts with those customarily performed for the purpose of model validation in compartment fires, which employ gas burners and so simplify much of the interaction. Initial experiments were carried out using a 0.23m diameter circular pan burning fixed amounts of heptane. Subsequently, a constant supply was used with a smaller circu- lar pan of 0.17m in diameter, in order to introduce experimental longevity under safe, controllable conditions whilst establishing a quasi steady-state system. Issues of non- stationarity in relation to heat-feedback to the fuel surface - an important pool fire mech- anism - are discussed. In addition to probe measurements of velocity and thermocouple temperature, the smoke yield was determined using a light extinction technique employing a 670nm wavelength diode laser and photo-diode detector, housed within a novel fully-traversible water- cooled probe. Data from these experiments illustrate the importance of accounting for room ventilation in terms of overall production of smoke and sound a cautionary note to the labelling of soot by a convenient marker such as temperature. Numerical simulation of the compartment fire is performed using the field model SOFIE, incorporating a simple evaporation model, which relates the mass-loss-rate of fuel to the net heat flux to the fuel surface and heat of gasification. This relationship assumes that heat losses to the pan, re-radiation by the fuel surface and other enthalpy loss terms, are small. Simulations of compartment fire scenarios using this model to calculate the rate of heat release are reported. Further comparisons are made between the industry stan- dard 'Eddy-Breakup' combustion model and the 'Laminar Flamelet' model. In general both the eddy-breakup model and laminar flamelet model tend to underpredict the yields of CO, whilst the eddy-breakup model over-predicts temperature and thus soot. The laminar flamelet approach shows more promise and shows particularly good agreement with the experimental measurements reported here under well ventilated conditions. SORE, the predictive tool employed in this research, has proved invaluable in discern- ing the reason for apparent ambiguities in the experimental measurements of soot con- centration. The results suggest that an alternative simplified zone model approach would overpredict visibility in smoke in terms of concentration, but underpredict in terms of layer depth, due to its inability to capture the important shape of the hot upper layer, which varies significantly from the homogenous, laterally uniform distribution which is assumed. The incorporation of a simple evaporation model which relies on accu- rate prediction of heat transfer in ultimately determining the heat release rate has been shown to be in very good agreement with the experiments. Despite the irregularity in predicted distribution of mass loss rate across the fuel surface - caused mainly due to the 'ray effect' of the radiation model - the main trend of lower heat transfer at the centre of the burner is demonstrated, in agreement with the experiments performed. This phe- nomenon is captured despite the lack of description of fuel vapour radiation blockage above the fuel surface, suggesting that this process may be disregarded. The heat flux distribution which is found here is in contrast to research conducted by other workers for similar sized pans in an open environment, which show a higher measured heat transfer at the centre of the burner. It has been shown that significant improvements could be made in experimental design of compartment fire experiments if CFD prediction is considered for the determination of suitable measurement locations in regions with lower local spatial variations.

The gas turbine fuel injector hs been the focus of considerable on-going research and development for over fifty years in order to satisfy the continuously evolving requirements with regard to combustion performance, fuel consumption and pollutant emissions. This exposition attempts to summarise the principal findings from the authors own research during the past two decades, and to identify their significance within the global framework of related studies in the area of gas turbine fuel injection. His recent studies on the structure of sprays in the near-nozzle region, encompassing simplex, pressure-swirl and engine-standard, pre-filming airblast atomizers, are characterised by an unparalleled combination of near-full power air density and liquid throughput, thereby extending significantly the knowledge database on the performance of these nozzles. They also served to reconcile the long-standing apparent contradictions in the open literature concerning the effect of ambient air pressure variation upon spray SMD for the simplex swirl injector. Moreover, they showed for the first time that the near-nozzle spray trajectory and overall mean drop size characteristics of the types of airblast nozzles used on engines are significantly different from those of the laboratory-scale atomizers featured in earlier research efforts. This is a reflection principally of the distinctive nature and scale of the fuel-air interactions involved in the two different environments. The new knowledge and understanding generated by the author's work on the plain-jet airblast concept has found practical application in large-scale industrial gas turbine engines. It is also contributing to the design of certain hybrid fuel injector configurations, which are now being offered either as an altemative to or in combination with the more established pre-filming concept. The limit of capability of both the laser sheet imaging technique developed by the author and the commercially available phase Doppler instrument have, for the first time, been successfully explored at the extreme conditions of high air density and high fuel throughputs encountered in modern gas turbines - yielding generally plausible isothermal spray property data.