The combustion of hydrocarbon based fuels is one of the worlds main sources of energy, with applications ranging from large scale industrial processes to transport. However, the use of these fuels has two keys problems, long term supply and emissions. In order to extend the use of hydrocarbon fuels and reduce their environmental impact, fundamental understanding of the combustion process is needed so that applications can be fully optimised. One of the most influential factors that effects the combustion processes is turbulence, a factor that significantly alters flame propagation and subsequent rates of heat release. It is this feature of combustion that is focused upon within this work. Initially flame-turbulence interaction is investigated using a fan stirred combustion bomb using high speed particle image velocimetry to examine the combustion of stoichiometric mixtures of methane and air. This study looks at how flame propagation effects turbulence and how different levels of turbulence effect flame structure. This work demonstrates that a flow field is significantly altered by a propagating flame, but that local turbulent structures are maintained ahead of it, structures that directly impact flame propagation. This section of work demonstrates that fundamental understanding is needed of how specific rotational flow structures, which characterise turbulent flows, effect local burning velocity. The rest of the work in this thesis details the study of the interaction between controlled toroidal vortices and a propagating flame front using a novel twin-chamber combustion bomb. As part of this study a new technique for the measurement of local burning velocity, using asynchronous particle image velocimetry, is developed and implemented; a technique which enables the quantification of local burning velocity within highly rotating flows. The information acquired using this new technique is then used to quantify the true local burning velocity by taking into account the translation of the flame via advection. Study of flame-vortex interaction in this manner is used to assess the impact of vortex structure on flame propagation rates. The burning velocity data demonstrates that there is a significant enhancement to the rate of flame propagation where the flame directly interacts with the rotating vortex. Away from this interaction with the main vortex core, the flame exhibits propagation rates around the value recorded for unperturbed combustion. Additional examination has shown that aspects of both the local flow field and the flame profile correlates with the local burning velocity; specifically flame curvature and the angle that the flame intersects the flame front.

In numerical modelling, Large Eddy Simulations (LES) has evolved itself as a powerful tool for the prediction of turbulent premixed flames. In LES, sub-grid scale (SGS) modelling plays a pivotal role in accounting for various SGS effects. Chemical reaction rate in LES turbulent premixed flames is a SGS phenomenon and must be accounted accurately. Flame surface density (FSD) models based on laminar flamelet concepts are simple and efficient in accounting the chemical reaction rate, which is the main motive of this research.

Increased efficiency and reduced emissions demands from users and legislative organisations have lead to the development of advanced combustion technologies for diesel engines. Exhaust gas recirculation (EGR) is a widely used technology to control diesel combustion and emissions, primarily to reduce emissions of oxides of nitrogen (NOx). Implementation of high levels of EGR (> 50%) is able to simultaneously reduce both emissions of NOx and particulate matter (PM) to ultra low levels. However, high EGR combustion is subject to reduced combustion efficiency and stability with increased total hydrocarbon (THC) and carbon monoxide (CO) emissions. This thesis presents research into low temperature diesel combustion (LTC) operation and the effects on combustion and emissions when the engine is operated under air, fuel and EGR rates encountered during transitions between LTC and conventional diesel operation modes. This has resulted in an improved understanding of the diesel combustion process and pollutant emissions with high rates of EGR, different fuel injection pressures and timings, post fuel injection and exhaust back pressures. The sensitivity of LTC to variations in engine speed, fuel injection quantity, and EGR rate and intake manifold temperature were investigated. Pseudo-transient operation of the engine was studied to interpret the transient performance of a diesel engine during transients within LTC and from LTC to conventional diesel combustion in a new European driving-cycle (NEDC) test. Experimental investigations were conducted on a single cylinder research diesel engine. Cylinder pressure, fuel consumption and gaseous and particulate emissions (filter smoke number, size distribution, and total number) were measured. The results showed that an increase in EGR rate can realise LTC on the research engine. Fuel injection parameters influenced the combustion phasing, and control of this was able to improve the combustion stability and to reduce the THC and CO emissions. The low smoke number for the LTC diesel combustion was a result of reduced mean particle size with possible changes in particulate composition. EGR is the most critical parameter influencing the LTC combustion and emissions. Transient simulation of an engine exhibits significant discrepancies in EGR rate and boost pressure. Pseudo-transient points at intermediate load condition showed significantly increased emissions, particularly smoke number. Retarded fuel injection timing and increased boost pressure were demonstrated to be an effective strategy to reduce smoke emissions for these pseudo-transient operating points.

The Polymer Electrolyte Fuel Cell (PEFC) is well-poised to play a key role in the portfolio of future energy technologies for civil and military applications. Principally, the PEFC converts part of the chemical energy released during hydrogenoxidation and oxygen-reduction into electrical energy, generating water a bi-product. It is potentially a zero-emissions technology which can operate silently due to the absence of any moving parts, has quick start-up characteristics and can achieve high thermodynamic efficiency. In order to ensure that the PEFC emerges as a viable option for all applications, it is necessary to ensure that the technology is reliable, capable of delivering performance and cost-effective throughout its life-cycle. To achieve these objectives, a better fundamental understanding of the mechanisms of electrochemical transport in the PEFC is required than is presently available. The literature identifies that multi-component electrochemical transport within the PEFC plays a central role in fuel cell operation and longevity. Water transport is one of these. It is well-understood that excessive amounts of water within the porous electrodes of the cell can cause flooding, which impedes the supply of reactant gases. It is also well-understood that insufficient water can cause the polymer electrolyte membrane (PEM) to dehydrate, thereby reducing its proton conductivity. Both of these processes can undermine cell performance. Repetitive hydration cycles are also known to precipitate degradation mechanisms which can undermine reliability. However, the mechanisms of multi-component and potentially two-phase transport across the PEFC as a multi-layered assembly which includes the porous electrodes and the PEM are not understood as well: the mechanisms of contaminant transport, fuel crossover and liquid water infiltration particularly through the PEM are important examples. The modelling literature demonstrates that electrochemical transport in the PEFC is treated either through the use of dilute solution theory or concentrated solution theory. The modelling literature also demonstrates a wide spectrum in the application of modelling assumptions and the formulation of electrochemical equations to simulate transport in the different layers of the PEFC. This thesis describes research aimed at reconciling the different modelling approaches and philosophies in the literature by developing and applying a unified mechanistic electrochemical treatment to describe multi-component, two-phase transport across the layers of the PEFC. The approach adopted here is first to construct a multi-component zerodimensional model for multi-component input gases which is merged with a multilayer PEFC model to correctly predict the boundary conditions in the gas channels based on the cross-flow of components through the cell. The model is validated using data from the open literature and applied to understand contaminant crossover from anode to cathode. The second step is to develop a unified mechanistic electrochemical treatment to describe multi-component transport across the layers of the PEFC: the general transport equation. This is central to the contribution of this thesis. It is theoretically validated by deriving the key transport equations used in the benchmark fuel cell modelling literature. It is then implemented with the multi-component input model developed previously and validated using data from the open literature. The model is subsequently applied to understand fuel crossover characteristics in the cell. The third and final step is to further-develop the application of the general transport equation to account for two-phase transport across the layers of the PEFC. The resulting model is validated against three different sets of data from the open literature and subsequently applied to understand the effects of PEM thickness, anode gas humidification, cell compression and PEM structural reinforcement on liquid infiltration and two-phase transport across the PEM. It is demonstrated that the general transport equation developed in this thesis establishes a backbone understanding of the modelling and simulation of transport across the layers of the PEFC. The study successfully reconciles the different modelling philosophies in the fuel cell literature. The progressive validation and application of the general transport equation demonstrates the potential to enhance the scientific understanding of factors affecting PEFC performance and demonstrates its value as a tool for computationally-based cell design, optimisation and diagnostics.

Thermal treatment is recognised as a valid option within the waste management hierarchy for the recovery of the energy content of waste. Recent developments in the field are signposted from emergent technologies and the standardisation of solid recovered fuels. This work comparatively examines the fluidized bed combustion and gasification of a novel material; East London’s solid recovered fuel. Emphasis is given on the characterisation of the solid residues produced from the two thermal treatment techniques and chlorine partitioning, in particular. Chlorine mass balances are studied under steady state conditions for combustion and gasification. Furthermore, trace metals content, chlorobenzenes, major elements, crystalline structures, and leaching behaviours are compared in the two residues types. For the characterisation of these residues a series of analytical methods have been applied and compared for their efficiencies. Results indicate that gasification produces 5-6 times less HCI than combustion. Furthermore, gasification residues retain higher amounts of CI and in less water soluble forms. However, gasification residues have 3-8 times higher organochlorides load, expressed chlorobenzenes. This work generates novel data on the comparative characterisation of waste thermal treatment residues. These data contribute towards the technical confidence for further utilisation of solid recovered fuels, and the knowledge over the residues’ properties.

The health and environmental risks due to airborne nanoparticles are important issues facing the citizens and governments of the industrialized countries. To assess and mitigate these risks, increasingly stringent regulations are being enacted to reduce the particulate emissions from the combustion of hydrocarbon fuels, which primarily consist of soot. Improvements to the understanding of the formation of soot nanoparticles and their impact on the health and the environment are required. This necessitates advances in the state of quantitative measurement of soot. Laser-induced incandescence (LII) is an optical diagnostic technique for the measurement of concentration and primary particle diameter of soot with high selectivity. Limitations with conventional LII were identified and a significantly enhanced technique, autocompensating LII (AC-LII), was developed employing time- resolved two-colour pyrometry, low fluence, and an absolute intensity calibration to address these limitations. AC-LII was shown to measure the soot particle temperature and automatically compensate for variations in the measurement environment that affected the peak soot particle temperature. With low fluence, AC-LII was shown to avoid soot sublimation, which impacted the measurements of concentration and size with high fluences. AC-LII was applied to flames and to combustion-generated emissions. At low ambient temperatures it was discovered that the measured concentration varied with fluence. To mitigate this issue, it was recommended that AC-LII be performed at a moderate fluence near the sublimation threshold. In order to assess the impact of distributions of the soot primary particle diameter and of aggregate size, analysis coupling experiments with a state-of-the-art numerical model of the heat transfer was performed. The results showed that AC-LII signal evaluation should begin immediately after an initial anomalous cooling period but before distribution effects become dominant. The sensitivity of AC-LII was optimized and applied to measure atmospheric black carbon concentrations. Comparison to other instruments demonstrated that AC-LII has significant advantages for the measurement of soot, and represents a major advancementin techniques for nanoparticle characterization.

Implicit Large Eddy Simulation (ILES) with high-resolution and high-order computational modelling has been applied to flows with turbulent mixing and combustion. Due to the turbulent nature, mixing of fuel and air and the subsequent combustion still remain challenging for computational fluid dynamics. However, recently ILES, an advanced numerical approach in Large Eddy Simulation methods, has shown encouraging results in prediction of turbulent flows. In this thesis the governing equations for single phase compressible flow were solved with an ILES approach using a finite volume Godunov-type method without explicit modelling of the subgrid scales. Up to ninth-order limiters were used to achieve high order spatial accuracy. When simulating non chemical reactive flows, the mean flow of a fuel burner was compared with the experimental results and showed good agreement in regions of strong turbulence and recirculation. The one dimensional kinetic energy spectrum was also examined and an ideal k−5/ 3 decay of energy could be seen in a certain range, which increased with grid resolution and order of the limiter. The cut-off wavenumbers are larger than the estimated maximum wavenumbers on the grid, therefore, the numerical dissipation sufficiently accounted for the energy transportation between large and small eddies. The effect of density differences between fuel and air was investigated for a wide range of Atwood number. The mean flow showed that when fuel momentum fluxes are identical the flow structure and the velocity fields were unchanged by Atwood number except for near fuel jet regions. The results also show that the effects of Atwood number on the flow structure can be described with a mixing parameter. In combustion flows simulation, a non filtered Arrhenius model was applied for the chemical source term, which corresponds to the case of the large chemical time scale compared to the turbulent time scale. A methane and air shear flow simulation was performed and the methane reaction rate showed non zero values against all temperature ranges. Small reaction rates were observed in the low temperature range due to the lack of subgrid scale modelling of the chemical source term. Simulation was also performed with fast chemistry approach representing the case of the large turbulent time scale compared to the chemical time scale. The mean flow of burner flames were compared with experimental data and a fair agreement was observed.

Environmentally friendly polymer electrolyte membrane fuel cells (PEMFCs) have the potential to revolutionise mobile power sources. One of the more promising PEMFC candidates is the direct methanol fuel cell (DMFC). Significant commercial interest has been expressed in the DMFC as a consequence of it becoming a possible replacement technology for batteries and internal combustion engines. The DMFC is a simple system that utilises liquid fuel and which requires minimal ancil lary equipment, and hence are more suited to the logistics of portable and vehicular applications than hydrogen fuel cells. However, significant technological challenges remain that must be addressed prior to the DMFC becoming more commercially exploitable. These challenges include improving the poor anode kinetics of methanol oxidation and reducing methanol crossover. To aid the understanding of the various factors limiting the widespread application of the DMFC, the statistical method of design of experiments was applied. A fractional factorial design was implemented to understand the main effects and interactions of a number of operating parameters on the overall performance of the DMFC, in which the effect of the crossover of methanol through the membrane was considered. The statistical models developed facilitated the detection of key two-factor interactions of temperature with methanol concentration, type of oxidant and cathode back pressure, which suggested that an improvement in DMFC performance was achievable by reducing the effect of methanol crossover. Based on the outcomes of the parametric study, response surface methodology was applied to optimise catalyst layer formulation. The response surface method highlighted the significance of high catalyst loading and the non-linear behaviour of the Nafion@ content. Furthermore, the advantage of adding PTFE in the anode catalyst formulation, to make the anode morphology favourable for carbon dioxide gas evolution, was demonstrated. Steady state semi empirical models for the anode based on methanol oxidation kinetics and cathode considering the effect of methanol crossover through the membrane were also developed. The kinetic models for the anode illustrated the significance of water and surface intermediates in the methanol oxidation reaction on a dual site Pt-Ru catalyst and highlighted the subtle balance between the methanol adsorption-dehydrogenation step and the subsequent oxidative removal step. The cathode model developed provided insight into the effect of methanol crossover on the cathode open circuit potential and helped in reliable estimation of the cathode polarisation curve. Finally a combination of these two models was used in the prediction of the cell polarisation characteristic as a function of cell potential, temperature and amount of methanol crossed over through the membrane

Harvesting and dewatering can account for up to 30% of the overall cost of production of usable microalgae biomass for the biotechnology and bioenergy sectors. Harvesting is particularly challenging due to the small amount of algal biomass produced relative to water volume. This process exacts high energy and cost demands and therefore limits further expansion in the microalgae biomass industry. Foam fractionation has potential to deliver a low cost, low energy harvesting solution. Microalgae cells adsorb to the surface of a stream of fine air bubbles, which then rise up a closed column, discharging the concentrated product at the top. Foam fractionation significantly reduces construction, maintenance, and energy costs compared to other harvesting technologies. In this research, a fractional factorial design of experiments followed by a central composite design were used to determine the optimal levels of major variables influencing the harvest of the freshwater microalga Chlorella sp. The effects of bubble size within the liquid pool and foam phase of the harvesting unit were determined, a high concentration factor of 427 as achieved using fluidic oscillation for microbubble generation. The influence of microalgal growth phase on harvest efficiency was investigated to gain insight into the optimal time to harvest during cell cultivation. The effect of surfactant, used to induce foaming, on lipid recovery was examined through methods including total lipid recovery, gas chromatography, energy dispersive x-ray spectrometry and solid phase extraction. The results indicate that the surfactant had the additional benefit of significantly increasing the overall lipid recovery. These encouraging results suggest foam fractionation offers considerable potential as an efficient, low cost, and scalable microalgae biomass harvesting technology.

Wind power is one of the world's fastest growing industries. The resulting penetration of wind power has led to substantial changes in requirements for large wind farms. Fault Ride-Through (FRT) was an important new requirement for wind farms to remain connected and actively contribute to system stability during a wide range of network faults. The wind industry responded with several approaches to FRT compliance including dynamic Reactive Power Compensation (dRPC) and pitch control. New requirements, combined with the reduced cost and increased efficiency of power electronic converters has led to the increasing dominance of Variable Speed Wind Turbines (VSWTs). Recent research has therefore focused on VSWTs. This Thesis presents a new technology, invented and developed during my PhD project, which provides a rearguard opportunity for Fixed Speed Wind Turbines (FSWTs) to comply with FRT requirementsu sing a series Dynamic Braking Resistor (sDBR). sDBR contributes directly to the balance of active power during a fault by inserting a series resistor into the generation circuit, increasing generator terminal voltage. The aim of the analysis, simulation and experimental work in this Thesis is to demonstrate the potential and scope of sDBR to contribute to FRT compliance of FSWTs. sDBR is shown to be a simple and effective means of displacing expensive dRPC to achieve full compliance with Great Britain's FRT requirements. It is also shown to be capable of contributing to compliance with the more onerous FRT requirements in conjunction with other technologies. Detailed transient simulations of sDBR were confirmed by experimental results using a 7.5kW test-rig. Although the FSWT market is severely weakened, opportunities remain in niche markets for new and existing wind farms. Continued research into high-speed switching, variable resistance and integrated control could further improve basic sDBR performance. Further research into new applications with distribution networks,s mall wind turbines and doubly-fed induction generators could also extend its application in new markets with longer horizons.