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Non-contact ignition of TIG welding arcs has been studied. The variation of dc voltage with dc current of combined acdc discharges indicated that an ac-dominated discharge, a dc-dominated discharge and a transition region exist during the initial current rise after breakdown from cold. These measurements enabled the conditions for reliable ignition of dc arcs using a continuous sinusoidal hf source to be predicted. The minimum current to sustain a cold arc and the time taken to reach the steady-state were investigated using a novel capacitor discharge supply. The results showed that to initiate a3 mm TIG welding arc from cold supplied by a power supply with an open circuit voltage of 80 V, a minimum current of about 0.9 A may be required and the time taken for the arc to reach the steady-state may take several hundred milliseconds. The results of investigations on combined ac-dc discharges, minimum current to sustain a cold arc and the time taken to reach the steady-state indicated that for safe, interference-free and reliable non-contact arc ignition, a continuous sinusoidal hf supply was the best method. A high voltage (about 3 kV) and high current (about 1 A) were required simultaneously to initiate a3 mm TIG arc from cold. A single continuous sinusoidal hf supply required an ignition power of the order of 1.35 kW which was not feasible. An arc ignition method using two continuous sinusoidal hf supplies has been devised which provides safe, interference-free and reliable arc ignition, and which requires less than 75% of the output power of a single continuous sinusoidal hf system. A solid-state hf ignition system based on the new method was designed and constructed.

Lean premixed swirl stabilised combustion is regarded as one of the most successful technologies for flame control and NOx reduction in gas turbines. Important characteristics of these flows are good mixing, flame stability through the formation of a Central Recirculation Zone, and low emissions at lean conditions as a consequence of the low operating temperature. This project presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process at various swirl numbers, nozzle geometries and gas compositions at same power outputs using confined and open conditions. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkölher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend and nozzle geometry, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. The Central Recirculation Zone was also measured and correlated to the blowoff phenomenon. A trend was found between the CRZ size/strength, the different compositions of gases used and the burner nozzle. Chemical kinetic analyses were carried out using PRO-CHEMKIN to determine flame speeds and chemical properties needed for CFD calculations. Experiments were performed using Phase Locked PIV and High Speed Photography. The Central Recirculation Zone and its turbulence were measured and correlated providing details of the structure close to blowoff. It was found that the nozzle angle has a small effect on the LBO at low flow rates using all mixtures. During the tests, the Coanda effect was observed with some geometries, thus further research was carried out regarding the transition of this phenomenon. It was found that the process occurs at a particular geometry and step size, with a shift in frequency produced by the leading structure due to the entrainment of air and strength of the latter. Stability of the flow occurs after a Coanda Vortex Breakdown (COVB) has occurred, a process similar to the one observed in the central region of the flow under regular swirling open flames. As the step size is increased, the COVB will evolve into a slower Trapped Vortex (TV).

The internal combustion engine (ICE) has been used in automotive vehicles without any significant improvement in energy efficiency for over a hundred years. There are several possibilities for developing a ‘greener’ and more powerful engine such as the homogeneous charge microwave ignition (HCMI) system. In this thesis, the HCMI system is analysed and investigated through simulation based ‘virtual prototyping’ in combination with an intelligent optimisation and a Computer-Automated Design (CAutoD) framework. The intention is to analyse and develop designs which could be used to transform the existing ICE ignition system to the HCMI system with minimal modifications to the existing engine. With the help of the finite element method (FEM), the microwave induced electromagnetic field in the engine cylinder is first simulated for `virtual prototyping' using a computer model. This then takes the prototyping methodology one step further, by replacing the process of human tuning of the prototypes with a computer-automated search process using computational intelligence. To realise this, an interface between the FEM model and the CAutoD framework is designed using the Application Programming Interface (API) of the FEM simulation software. This connection facilitates a rapid exchange of data between the simulation model and the search algorithm. Thus, rendering it possible to accommodate a wider exploration or a higher simulation resolution for superior and more accurate prototyping. Another contribution of this thesis is the improvement of the search performance, including the combination of deterministic and non-deterministic search algorithm as well as using a new technique to solve optimisation problems without using the frequency as an input variable. The knowledge gained from the analysis of nature-inspired algorithms is used to perform a pre-evaluation and hence to provide a population which guides a non-deterministic search towards potentially optimal directions for the global maximum. A CAutoD system is then developed to optimise digital prototyping on various aspects of the ignition device for the HCMI system. This helps deepen the understanding of relationships between the characteristic outputs of a design, and the input parameters that affect the performance of the device. The CAutoD system is first applied to a basic cylinder model, with one single antenna in the middle, to analyse the single variable changes for the antenna designs. It is discovered that the inner antenna length has a significant impact on the maximum electric field intensity inside the engine cylinder. Then it is applied to the design process involving multiple variable changes for the global optimum electromagnetic performance. The results are presented in multi-dimensional graphs, which illustrate the relevant relationships between the different input variables. For example, it is revealed that the resonance frequency is affected more by the piston position than by the antenna length, which underlines the importance of the correct and exact timing advance and control of the ignition event. Subsequent to the extensive and systematic analysis of different antenna designs and input variables, Computer-Automated Design (CAutoD) has been applied to various designs to expand the understanding and virtual prototyping of the HCMI system. The criterion for the best design is to first provide the highest possible electromagnetic propagation performance within the cylindrical cavity by using the lowest microwave input power. With this, the reection of the microwave energy from the cylinder back to the microwave source, under the geometric conditions of the cylinder and antenna model, will also be minimised. During the search process, the default antenna model was extended with an additional antenna, which leads to a dramatic decrease in the field, once the additional antenna is introduced. This determines, that any antenna at the outer shield of the coaxial cable and inside the cylinder head, interferes with the electromagnetic propagation inside the cavity and lowers the propagation performance. The results show that this field will break down the air-fuel mixture inside the cylinder because the field strength is comparable to that, created by a spark plug. Hence, a HCMI system can be designed to replace a spark ignition system without requiring physical modifications to the engine cylinder.

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A condition monitoring program applied to diesel engines, improves safety, productivity, increases serviceability and reduces maintenance costs. Investigation of a novel condition monitoring systems for diesel engine is attracting considerable attention due to both the increasing demands placed upon engine components and the limitations of conventional techniques. This thesis documents research conducted to assess the monitoring capabilities used acoustic emission (AE) analysis. It focuses on the possibility of using AE signals to monitor the fuel injector and oil condition. A series of experiments were performed on a JCB, four-stroke diesel engine. Tests under healthy operating conditions developed a detailed understanding of typical acoustic emission generation in terms of both the source mechanisms and the characteristics of the resulting activity. This was supplemented by specific tests to investigate possible acoustic emission generation due to the piston slap and friction. The effect of faults on the injector waveform was investigated using the injection system and at one sensor location. To overcome the reflections and injection system configuration effects the method of acoustic emission impedance was used. This enabled the injector signal to be successfully extracted and clearly shows its capability for detecting even minor combustion deviations between engine cylinders. Comparison between signals and measurement of the oil condition showed both provided useful information about the lubrication processes. Simulation and experimental work have demonstrated the capability of this technique to detect lubrication related faults and irregular lubrication variability between the engine's cylinders. A review of the AE sources in diesel engines and how to represent the AE signals generated is presented. Three analysis methods were used: time-domain analysis using parameters such as Root Mean Square (RMS), variance, mean and kurtosis; frequency-domain analysis which relied on the amplitudes of the frequency components of the measured signals; and time-frequency domain analysis extracting features so that the energy content of the signals and the frequency components were localized simultaneously. In this work, data has been obtained from tests on a diesel engine, where the engine load, speed, temperature and the oil lubrication type were changed. The monitored signal and its difference from that obtained for normal engine conditions was noted as a fault signature that could be used for fault detection and diagnosis.

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