Petrol internal combustion engines (ICEs) in automobiles use a high-voltage spark ignition system, which currently offers an energy efficiency of 25%-35% only and also produces excessive exhaust emissions. Recent political, economic, social, technical, legal and environmental drive has accelerated the worldwide research in ‘greener’ engines, such as the homogenous charge compression ignition (HCCI) engines, which focuses on total resource conservation and emission reduction per mile. However, its ignition timing needs real-time control of cylinder pressure and temperature in a closed loop, which is practically intractable to date. Leapfrogging HCCI and requiring no closed-loop control or modification to the engine, this thesis develops homogenous charge microwave ignition (HCMI) directly to replace the point-based spark ignition. Like HCCI, HCMI is volume based and is also applicable to diesel fuel. Through computer simulations, the thesis verifies the feasibility of the ICE radio frequency ignition concept first proposed by Ward in 1974. Building on the simulation-based design methodology of Boeing 777 aircraft, which required no hardware casting or prototyping at the design stage, this thesis employs intelligent search to evolve ‘designs of experiments’ by simulation means for vehicle-borne HCMI with potential to offer a step change in fuel efficiency and emission reduction. Investigation of this thesis into the effect of piston position confirms with graphical visualisation that the resonant frequency of the engine cylinder is very sensitive to the piston motion, because it can easily cause off-resonance and hence degraded field strength. It is revealed that this is the major factor that encumbers practical realisation of an HCMI system. This thesis shows that the natural frequency changes 0.015 GHz per 0.5 mm in average when the piston moves from 5 mm to 0.5 mm TDC and 0.0021 GHz per 0.05 mm when the piston moves from 0.5 mm to 0.05 mm to TDC. For the geometry of the given ICE cylinder, if the input microwave frequency is fixed, the resonance lasts for 7 s. Investigation on various diameters of cylinders that reveals the results on the effects of piston motion of a certain cylinder can be extended to other cylinders with different diameters. It is also shown that for different types of cylinders the frequency of input microwave can be very different. Therefore, the different microwave source of the HCMI systems has to be designed for different types of vehicles. Simulations reported in the thesis also reveal that a microwave based ignition takes 30 ns to 100 ns to break down the median of a permittivity and permeability that are the same as the chemically optimal 14.7:1 air-fuel mixture. This is much shorter than the duration of the microwave resonance and hence makes HCMI feasible in terms of duration. For a running engine, the variations of AFR can also cause off-resonance. It is found that the AFR does not affect the resonant frequency as much as piston motion does. The frequency only changes 38MHz when the AFR varies from 10:1 to 16:1. Properties and effects of microwave emitter and couplers are also studied and the results confirm with graphical visualisation that, for an emitter in the form of a probe antenna, the electric field intensity is dependant on the antenna length. For the given geometry of the Chryslor-Dorge ICE studied, a probe antenna of a length around 30% of wavelength shorter than the end of transmission line offers the best coupling efficiency in an HCMI system. To search for globally optimal designs, the Nelder-Mead simplex method and the ‘intelligent’ evolutionary algorithm (EA) are coupled with CAD simulations. These machine learning methods are shown efficient and reliable in dealing with multiple parameters. Under practical constraints, the best ignition timing and AFR combination is found, which for a 100 W input offers an electric field intensity of up to 9.8×106 V m-1, almost doubling the minimum requirement of 5.5×106 V m-1 for a plasma breakdown of the air-fuel mixture. In this work, six different geometric shapes of antennae are studied. Through the EA based global search, it is confirmed that the length and screen radius of the probe antenna do not affect the resonant frequency significantly. For the given ICE geometry, an antenna length of 14.3 mm offers the best efficiency and the least reflection regardless of the screen radius. The radius affects resonance the least among all the parameters searched, although it can contribute to enhancing electric field and reducing reflection of the coupling. For maximal electric field strength in the cylinder, the best combination of the antenna length and the screen radius is also searched and results are fully tabulated in this thesis.

Sound Quality engineering (SQE) is a discipline that should be embedded within Noise Vibration and Harshness (NVH) engineering. Its purpose is to tailor and enhance a vehicle’s sound in order for it to meet and / or exceed the customers’ expectations of the car and of the brand. NVH engineers need to use the opinions of customers, key decision makers in the organisation and those of their colleagues to set objective NVH targets for new vehicles. Their opinions are captured through jury evaluations. Interactive simulation is a new approach to presenting sounds to a jury. It enables assessors to evaluate existing and concept cars generated in real time and before the manufacture of physical prototypes. This document summarises the research carried out for the EngD research programme. Its aim was to develop methodological approaches for setting up evaluations using interactive simulation, optimise its data capture and analysis capabilities and provide insight, to NVH engineers, into how assessors evaluate sound quality. The first stage of the research involved benchmarking how the interactive simulation tool was being used by its developers, and how NVH targets are set within an OEM. This provided the foundation upon which to build the new methodology. The benchmark was compared against methodological approaches used in experimental psychology and in other sensory perception practices. This identified that principles for the design of evaluations had not been considered and appropriate statistical analysis techniques were not being implemented. Therefore it was not possible to ensure if the differences observed in the results were significant or not. It also became apparent that as each assessor was free to drive vehicles however they wished, the NVH engineers would not be able to link the assessor’s subjective impressions with the acoustical stimuli used to form an opinion. This was due to the lack of observational methods that could be applied. In addition, the use of this form of interactivity was novel compared to the approaches available before the introduction of the simulation. Therefore it was not yet understood how it could influence the outcome of the evaluations. An iterative approach was adopted to develop both tools and methods. Following the benchmarking stages, experimental design principles were implemented and a structured briefing method was formulated for the first time. These contributed to the overall methodologies and were also used to ensure the studies conducted as part of this research programme were free from experimental biases. This stage was followed by identifying a statistical analysis framework which can be used to study the assessors’ subjective impressions. These contributions enable the NVH engineer to understand if the differences observed between sounds are significant or not. The next phase was to understand how to best capture subjective opinions. Recommendations for this were based on the purpose of the evaluation. For the benchmarking stages of the NVH target setting process, many cars are often evaluated and therefore the duration of the evaluation can be a concern. However, the desired level of accuracy of the results is not as high as it is for the validations stages, upon which key engineering decisions are based, and also fewer cars are evaluated. Taken together it was possible to recommend the use of scaled interfaces for the benchmarking stages and the paired comparison method for the validation stages. The former takes less time to complete than the latter, which is however more accurate. The data capture capabilities were further enhanced through the development of a driver observation module; this enabled the assessor’s assessment strategies to be recorded. The data collected provided insight into how assessors drove with the aid of new visualisation and analysis techniques developed. Given the availability of these new methods and tools it was then possible to use the simulator to observe the influence of interactivity on the outcome of the evaluation. This demonstrated that assessment strategies can vary depending on the question asked to the assessor. The study indicated that assessors associated the refinement character of a car with driving conditions other than those presented to them in traditional evaluations. Through the research and developments of this EngD programme, NVH engineers can now observe with confidence if differences between sounds are significant and they can see and hear how the assessor made decisions. Therefore they can now link subjective impressions formed with the stimuli evaluated by the assessor, hence an effective way of using the simulator has been proposed.

This thesis was initiated by the need to develop a stable low vibration engine with a high power to weight ratio. A new rotary (Wankel) engine was chosen to meet these requirements. A further operating criterion was that the engine was required to use JP8 (aviation fuel). The difficulty created by the use of JP8 is that its combustion temperature is higher than other conventional fuels, and preheating is necessary, especially in the case of cold start. Thus, the question posed was, could a more appropriate and efficient method of fuel delivery be devised? This thesis presents the design and construction of a fluid spray visualisation system for investigating the macroscopic and microscopic characteristics of fuel sprays using low injection pressure up to 10 bar (1 MPa). Laser imaging techniques have been used for data acquisition. The thesis has been divided into several aspects. Firstly, a background study of fluid sprays and fuel injection strategies was carried out. This has centred on the relationship between droplet size and the combustion process. It further investigated what differentiated the fuel delivery approach to Wankle from that to other engines. Secondly, two families of fuel injector were tested and evaluated within the optical engineering laboratory using deionised water (DI) water for safety reasons. The first family involved conventional gasoline injectors with several nozzle arrangements. The second family involved medical nebulisers with several nozzle diameters. The evaluation of the fuel injectors required developing a fluid delivery circuit, and a specific ECU (Electronic Control Unit) for controlling pulse delivery and imaging instrument. The company associated with the project then set up a test cell for performing experiments on JP8 fuel. The initial global visualisation of the jet spray was made using a conventional digital camera. This gave a measurement of the spray angle and penetration length. However, as the study moved to the more precise determination of the fuel spray particulate size, a specialised Nd:YAG laser based diagnostic was created combined with a long range diffraction limited microscope. Microscopic characterisation of the fuel sprays was carried out using a backlight shadowgraph method. The microscopic shadowgraphy method was applied successfully to resolve droplets larger than 4 microns in diameter. The spray development process during an individual fuel injection cycle was investigated, presenting the frequency response effect of electronic fuel injectors (EFI) on the spray characteristics when operating at high injection frequencies (0.25 -­‐ 3.3 kHz). The velocity distribution during the different stages of an injection cycle was investigated using PIV. The influence of the injection pressure on the spray pattern and droplet size was also presented. Novel fluid atomisation systems were investigated for the capability of generating an optimum particulate distribution under low pressure. Finally, it was found that a new electronic medical nebuliser (micro-­‐dispenser) could be used to deliver the fuel supply with the relevant particle size distribution at low flow rate and high injection frequency. However, as yet it has not been possible to apply this approach to the engine; it is hoped that it will yield a more efficient method of cold starting the engine. The characteristics of this atomiser can be applied to provide a controllable fuel supply approach for all rotary engines to improve their fuel efficiency. The second part of this research discusses the droplets-­‐light interaction using Mie scattering for fluid droplets smaller than the microscope visualisation limit (4 microns). Mie scattering theory was implemented into Three-­‐Components Particle Image Velocimetry (3C-­‐ PIV) tests to address a number of problems associated with flow seeding using oil smoke. Mie curves were used to generate the scattering profile of the oil sub-­‐micron droplets, and therefore the scattering efficiency can be calculated at different angles of observation. The results were used in jet flow PIV system for the determination of the optimum position of the two cameras to generate balanced brightness between the images pairs. The brightness balance between images is important for improving the correlation quality in the PIV calculations. The scattering efficiency and the correlation quality were investigated for different seeding materials and using different interrogation window sizes.

The demand for electrical power has consistently risen over time, whether it be to support the development and expansion of cities or because traditional approaches to societies solutions are being replaced by their electrical equivalent. The automotive industry is beginning to introduce more electric, greener vehicles. The aviation industry is also being challenged with the same issues. Whatever the motivation, this rising demand for power is always facilitated by employing higher and higher voltage levels. It is well understood that if the voltage is too high for a given air gap, electric breakdown will occur. this effect is exacerbated by increases in altitude, resulting in constant challenges in aviation to satisfy the contradictory demands for smaller/lighter compact solutions against the biggest possible air gaps necessary to prevent electric breakdown. An experimental curve by Louis Karl Heinrich Friedrich Paschen was developed, which relates the voltage at which electric breakdown would be expected to that of the product of gas pressure (p) and distance (d). The aviation industry does not use this curve directly as alternate guidance documents are used. These documents are extremely conservative, sometimes overly so, as will be seen in the thesis. Mathematical attempts have been provided to try and explain the Paschen curve, based on Townsend Primary and secondary ionisation. However, the variable 'pd' does not get explicitly linked and a type of mathematical fudge becomes incorporated. This thesis attempts to provide a theory of the minimum electric breakdown curve and fundamentally link he 'pd' product. by experimental validation of the theory, with the accepted standards included. A basis for challenging these standards may result and prevent potential over engineering in the future in this continually challenging environment. This theory will then go on to explain arc formation by providing a treatment to a paradox that occurs at the point of breakdown.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

Many asteroids and comets orbit the inner solar system; among them Near Earth Objects (NEOs) are those celestial bodies for which the orbit lies close, and sometimes crosses, the Earth’s orbit. Over the last decades the impact hazard they pose to the Earth has generated heated discussions on the required measures to react to such a scenario. The aim of the research presented in this dissertation is to develop methodologies for the trajectory design of interception and deflection missions to Near Earth Objects. The displacement, following a deflection manoeuvre, of the asteroid at the minimum orbit intersection distance with the Earth is expressed by means of a simple and general formulation, which exploits the relative motion equations and Gauss’ equations. The variation of the orbital elements achieved by any impulsive or low-thrust action on the threatening body is derived through a semi-analytical approach, whose accuracy is extensively shown. This formulation allows the analysis of the optimal direction of the deflection manoeuvre to maximise the achievable deviation. The search for optimal opportunities for mitigation missions is done through a global optimisation approach. The transfer trajectory, modelled through preliminary design techniques, is integrated with the deflection model. In this way, the mission planning can be performed by optimising different contrasting criteria, such as the mass at launch, the warning time, and the total deflection. A set of Pareto fronts is computed for different deflection strategies and considering various asteroid mitigation scenarios. Each Pareto set represents a number of mission opportunities, over a wide domain of launch windows and design parameters. A first set of results focuses on impulsive deflection missions, to a selected group of potentially hazardous asteroids; the analysis shows that the ideal optimal direction of the deflection manoeuvre cannot always be achieved when the transfer trajectory is integrated with the deflection phase. A second set of results includes solutions for the deviation of some selected NEOs by means of a solar collector strategy. The semi-analytical formulation derived allows the reduction of the computational time, hence the generation of a large number of solutions. Moreover, sets of Pareto fronts for asteroid mitigation are computed through the more feasible deflection schemes proposed in literature: kinetic impactor, nuclear interceptor, mass driver device, low-thrust attached propulsion, solar collector, and gravity tug. A dominance criterion is used to perform a comparative assessment of these mitigation strategies, while also considering the required technological development through a technology readiness factor. The global search of solutions through a multi-criteria optimisation approach represents the first stage of the mission planning, in which preliminary design techniques are used for the trajectory model. At a second stage, a selected number of trajectories can be optimised, using a refined model of the dynamics. For this purpose, the use of Differential Dynamic Programming (DDP) is investigated for the solution of the optimal control problem associated to the design of low-thrust trajectories. The stage-wise approach of DDP is exploited to integrate an adaptive step discretisation scheme within the optimisation process. The discretisation mesh is adjusted at each iteration, to assure high accuracy of the solution trajectory and hence fully exploit the dynamics of the problem within the optimisation process. The feedback nature of the control law is preserved, through a particular interpolation technique that improves the robustness against some approximation errors. The modified DDP-method is presented and applied to the design of transfer trajectories to the fly-by or rendezvous of NEOs, including the escape phase at the Earth. The DDP approach allows the optimisation of the trajectory as a whole, without recurring to the patched conic approach. The results show how the proposed method is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution.

Suborbital flights will soon take flight as a viable commercial operation. Operators such as Virgin Galactic, along with their designer Scaled Composites, will be responsible for safety of the flight crew, Spaceflight Participants and indeed the uninvolved public beneath their flight trajectories. Within the United States, the Federal Aviation Authority’s Office of Commercial Transportation (FAA-AST) has provided Launch License Regulations and Guidelines for prospective design organisations and operators alike. The aim of this thesis is to analyse suborbital spaceflight approaches to safety management and to determine whether effective safety management is being or could be applied to influence vehicle design and subsequent operation. The thesis provides a review of current safety-related information on suborbital spaceflight, existing space safety information and also existing aviation safety information. The findings of the review concern two main areas; firstly that a gap exists within suborbital safety management criteria, and secondly that a gap exists in existing aviation-based safety guidelines. In the first case, the research concluded that FAA-AST safety management criteria did not present sufficiently explicit and rationalised guidelines for this new industry. Indeed, the thesis argues that the scope of the FAA-AST regulations (covering both orbital and suborbital aspects) is too broad, and that regulations and guidelines should be split into distinct orbital and suborbital sections so as to provide more effective directives. In Europe, no such regulations or guidelines exist as there has until now been no requirement (a ‘customer’) for the European Aviation Safety Agency (EASA) to implement such a framework. This thesis sought to address this gap by using a safety tool (Goal Structuring Notation) to construct a goal-based regulatory approach, which was included in a draft EASA suborbital Policy. Secondly, the main significant finding of this research is that a gap (literally) exists between current aviation-based design organisation safety guidelines and operator safety risk management guidelines. This absence of communication means operators are not managing their safety risks as effectively as they could. The thesis argues that the suborbital domain should take heed, as most vehicles are based on aircraft designs and therefore suborbital operators will, no doubt, apply ‘best practice’ either from the aviation or commercial space domains. Neither is appropriate or effective. As a result of the main finding a contiguous safety model has been developed which employs a ‘key (platform) hazard’ to join the design organisation analysis to the operator safety risk management, therefore completing an explicit sequence from the initiating causal event to the accident. The model is demonstrated using case studies from space disasters (Space Shuttle) and also from aviation accidents (Air France flight AF447); the model details the explicit accident sequence and shows missing or failed controls leading up to the accident. The research enabled models to be constructed and also proposed additional and explicit guidelines for the suborbital industry such as medical and training standards and separate safety criteria for vertical launch vehicles; these are included as recommendations and need to be ratified by recognised bodies such as the International Association for the Advancement of Space Safety’s Suborbital Space Safety Technical Committee for inclusion in their Space Safety Standards Manual. In the latter case these recommendations are already agenda items for the Technical Committee to address.

The research in this thesis deals with nonlinear control of spacecraft attitude stabilization and tracking manoeuvres and addresses the issue of control toque saturation on a priori basis. The cascaded structure of spacecraft attitude kinematics and dynamics makes the method of integrator backstepping preferred scheme for the spacecraft nonlinear attitude control. However, the conventional backstepping control design method may result in excessive control torque beyond the saturation bound of the actuators. While remaining within the framework of conventional backstepping control design, the present work proposes the formulation of analytical bounds for the control torque components as functions of the initial attitude and angular velocity errors and the gains involved in the control design procedure. The said analytical bounds have been shown to be useful for tuning the gains in a way that the guaranteed maximum torque upper bound lies within the capability of the actuator and, hence, addressing the issue of control input saturation. Conditions have also been developed as well as the generalization of the said analytical bounds which allow for the tuning of the control gains to guarantee prescribed stability with the additional aim that the control action avoids reaching saturation while anticipating the presence of bounded external disturbance torque and uncertainties in the spacecraft moments of inertia. Moreover, the work has also been extended blending it with the artificial potential function method for achieving autonomous capability of avoiding pointing constraints for the case of spacecraft large angle slew manoeuvres. The idea of undergoing such manoeuvres using control moment gyros to track commanded angular momentum rather than a torque command has also been studied. In this context, a gimbal position command generation algorithm has been proposed for a pyramid-type cluster of four single gimbal control moment gyros. The proposed algorithm not only avoids the saturation of the angular momentum input from the control moment gyro cluster but also exploits its maximum value deliverable by the cluster along the direction of the commanded angular momentum for the major part of the manoeuvre. In this way, it results in rapid spacecraft slew manoeuvres. The ideas proposed in the thesis have also been validated using numerical simulations and compared with results already existing in the literature.

A means of conducting continuous payload exchanges between the Earth and Moon would allow materials to be transported between them on a regular basis and could be used to supply vital resources to a permanent lunar colony. In addition to this, it could provide a means of returning materials, extracted from the mineral rich lunar surface, back to Earth. The use of symmetrically laden motorised momentum exchange tethers would allow these transfers to be conducted free of any conventional propulsion, purely by the exchange of momentum between the payloads, and without the subsequent loss of orbital altitude experienced by asymmetrical tether configurations. Although this is an exciting prospect it is not without its challenges, for example, if the Moon orbited a spherical Earth adhering to Kepler's laws, the transport of materials would be conducted with clockwork precision and the colonisation of the Moon would already have taken place. However, Kepler's laws are idealised to the two body motion of perfectly spherical bodies and are applicable only in the most simplified of circumstances. The Moon's motion is in reality complex and the establishment of such a system is made even more so by the oblateness effects of a non-spherical Earth acting on the tether system in Earth orbit. Adding to this complexity is the less significant but noticeable effect of the Moon's oblateness acting on a tether in lunar orbit. Other challenges include the design of a device to capture the payloads at the tether's tips at orbital velocity in addition to effecting their release at the correct instant; and the tether system's reaction to mechanical shocks which are a real possibility if velocity mismatches between the tether tips and payloads are significant. Restricting the scope of this investigation, the aim of the following is: to determine whether such a system can be realistically established when taking into account the complex nature of the Moon and resulting opportunities for payload exchanges; to establish the logistical design of the system required to conduct these regular two-way exchanges; to determine suitable configurations of the Earth and Moon orbiting tethers for conducting these exchanges when planetary oblateness effects are taken into account in addition to the complex motion of the Moon about Earth; to configure the trajectory design of the payloads between these tethers such that the logistical requirements are satisfied; and finally to investigate an anomaly observed whilst conducting simulations of the motion of a symmetrically laden tether in orbit about Earth which relates to the theory behind the concept of gravity gradient stabilisation.