This research has focused on obtaining a comprehensive understanding of gasoline direct injector coking effects on fuel injection, engine performance and emissions. The impact of spark plug electrode gap on flame kernel development, engine performance, and emissions was also investigated. In this study, the deposit build-up inside the injector nozzles and on the injector tips reduced the plume cone angle, while it increased the plume penetration length, plume separation angles, mean droplet velocity and size for the coked injector. The coked injectors showed a higher degree of inhomogeneity and poorer repeatability in mixture preparation. The combustion analysis demonstrated that the coked injectors showed lower load and lower combustion stability, compared with the clean injector under the same operating conditions. The increase of the spark plug gap resulted in an increase for the flame kernel growth area. The maximum in-cylinder pressure, turbulent flame speed, heat release rate and the mass fraction burned increased with the spark plug gap. The engine output increased slightly and the combustion process became more stable due to the reduction in cyclic variations as the spark plug gap increased. With the maximum spark plug gap, the engine produced minimum hydrocarbon emissions and particulate number concentration.

The requirements for controlling Particulate Matter (PM) and gaseous emissions emitted from gasoline direct injection (GDI) engines, especially under cold start conditions, and the introduction of bio-alcohols fuels in the market demands the development of novel efficient aftertreatment technologies. Understanding the PM characteristics from the combustion of different fuels it is a key step in the design of next generation of catalysts and aftertreatment systems, including three-way catalyst (TWC) and catalyst coated or not gasoline particulate filters (GPFs). The research study presented in this thesis provides a detailed understanding of the synergies between bio-alcohols derived fuels combustion in GDI engines and novel aftertreatment technologies on the control of PM and gaseous emissions. The effect of the physico-chemical properties of bio-alcohol fuel blends on combustion and emissions at warm steady-state and cold start engine conditions has been investigated. Bio-butanol fuel blend has been further explored at different engine loads in combination with exhaust gas recirculation (EGR) technology. An extensive characterization of the PM emissions has been carried out using several methodologies and techniques such as high resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), scanning mobility particle sizer (SMPS) and Raman spectroscopy. The combustion of bio-alcohols resulted in a significant reduction of 60% - 80% of PM emissions with the modification in their structural characteristics, leading to agglomerates with smaller primary particles (≈1-3 nm) and fractal dimensions and, soot with higher tortuosity (≈3.1 %) as TEM revealed. Under cold start event, bioalcohols emitted more reactive and less mature soot (i.e. higher organic content and impurities) as found from TGA and Raman analysis compared to soot emitted from gasoline fuel combustion. The TWC activity was improved between 4.3% and 1.5% in the exhaust stream from the bio-alcohols combustion. The aftertreatment architectures, including either coated GPFs or not and arrangement in the exhaust (i.e. upstream or downstream of the TWC) has shown a significantly impact on the TWC activity, reducing light-off temperatures up to 20°C. Catalytic GPF showed high performance to efficiently filter PM and removed gaseous emissions from GDI combustion with acceptable pressure drop.

The research involves the investigation of hybrid ultrasonic assisted creep feed grinding (UACFG) of advanced aeroengine alloys, in particular Inconel 718, CMSX-4 and gamma titanium aluminide (γ-TiAl). For tests with ultrasonic vibration, workpieces were actuated at a constant frequency (~20kHz) via a specially designed block sonotrode attached to a 1kW piezoelectric transducer-generator system. The trials on nickel based superalloys were carried out using open structured alumina wheels whereas γ-TiAl specimens were machined with conventional silicon carbide and single layer diamond superabrasive wheels. Statistically designed experiments involving variation in wheel speed, table speed, depth of cut, grinding condition and vibration amplitude were employed in mainstream testing. Reductions in grinding force components were typically observed albeit at the cost of higher wheel wear and surface roughness of the ground slots when ultrasonic assisted grinding of nickel alloys. Conversely, UACFG of γ-TiAl exhibited lower grinding wheel wear and workpiece surface roughness. Surfaces ground with the assistance of vibration generally revealed greater side flow/ploughing and overlapping grit marks in comparison to standard creep feed ground specimens. Three dimensional topographic measurement of grinding wheel surface replicas indicated that ultrasonic vibration led to an increase in the number of active cutting points on the wheel.

In order to accurately predict vehicle dynamic properties when tires impact high obstacles or large bumps, appropriate tire models need to be developed and characterised. The Flexible Ring Tire (FTire) model is one of the models for predicting the transient dynamic responses when traversing obstacles. In this thesis, a combination of experimental tests and Finite Element (FE) modelling is used in deriving FTire models for different levels of tire/road interaction severity. A FE tire model is built to characterize tire properties including static properties, steady-state rolling properties and transient dynamic rolling properties. A 235/60 R18 tire is cut in order that the tire cross-section can be captured and the tire rubber and reinforcement components can be extracted. A detailed method for the determination of geometrical and material properties of tires has been developed for tire modelling. The 2D and 3D models for static and dynamic analysis are both developed using a commercial FE code ABAQUS. The parameters of FTire model are derived based on the experimental data and FE simulation data, and different FTire models are derived under different operation conditions. Multi-body dynamic analysis is carried out using these FTire models, and the transient dynamic responses using different FTire models are compared with each other. It is shown that FE modelling can be used to accurately characterise the behaviour of a tire where limitations in experimental facilities prevent tire characterisation using the required level of input severity in physical tests.

This PhD project is set out to develop a type of hybrid journal air bearings with reduced reliance on the supply of compressed air for mobile turbomachinery applications. The research work covers hydrostatic and hybrid journal air bearings with non-compliant clearance boundaries. The approach adopted combined numerical analysis based on CFD and experimental verification of the designs. The research can be divided into three sections. In the first section, numerical approaches to model hydrostatic and hybrid journal air bearings with a fixed clearance boundary were developed based on finite difference method (FDM) and finite volume method (FVM) respectively. In the second and third section, theoretical and experimental studies were performed on hydrostatic and hybrid journal air bearings. Performance of the bearings was investigated in non-rotational and rotational conditions. The analysis on stability and natural frequencies of rotor bearing system was performed using the linear bearing model. The unbalance responses of the rotor in the test rig were predicted using non-linear transient analysis and measured experimentally from 50k rpm to 120k rpm in rotor speed. Through the theoretical and experimental investigations of the hybrid journal air bearings, the objectives of the project have been implemented and the aims have been met.

This thesis summarise the results of an investigation of the tribological interactions of the human finger pad with different surfaces and tactile displays. In the wide range of analyses of the mechanical properties of the finger pad, an attempt has been made to explain the nature of the interactions based on critical material parameters and experimental data. The experimental data are presented together with detailed modelling of the contact mechanics of the finger pad compressed against a smooth flat surface. Based on the model and the experimental data, it was possible to account of the loading behaviour of a finger pad and derive the Young’s modulus of the fingerprint ridges. The frictional measurements of a finger pad against smooth flat surfaces are consistent with an occlusion mechanism that is governed by first order kinetics. In contrast, measurements against a rough surface demonstrated that the friction is unaffected by occlusion since Coulombic slip was exhibited. The thesis includes an investigation of critical parameters such as the contact area. It has been shown that four characteristic length scales, rather than just two as previously assumed, are required to describe the contact mechanics of the finger pad. In addition, there are two characteristic times respectively associated with the growth rates of junctions formed by the finger pad ridges and of the real area of contact. These length and time scales are important in understanding how the Archardian-Hertzian transition drives both the large increase of friction and the reduction of the areal load index during persisting finger contacts with impermeable surfaces. Established and novel models were evaluated with statistically meaningful experiments for phenomena such as lateral displacement, electrostatic forces and squeeze-film that have advanced applications.

This thesis provides new methodologies to improve the simulation of the orthogonal cutting of unidirectional carbon fibre reinforced plastic (UD-CFRP) composites. In a meso-scale approach, a new cohesive model was developed to overcome the excessive deformations shown by the generally implemented zero thickness cohesive elements. The smoothed particle hydrodynamics (SPH) approach was implemented to avoid element deletion during the analysis, taking place in the commonly used finite element method (FEM). The SPH enabled better prediction of the thrust force, more realistic chip formation mechanisms and the capability to simulate the bouncing back. However, the absence of a cohesive layer did not permit the collection of information on the interface behaviour. Therefore, a hybrid model, based on the FEM to SPH conversion, was deployed to introduce a cohesive layer, while avoiding element deletion. In-house experiments were conducted for validating the hybrid model. The hybrid approach consented implementation of the novel cohesive model while improving the thrust force prediction when compared with the FEM. It was able to capture the effect of a round cutting edge, as was highlighted in the experimental results. Experiments highlighted the strong influence of the rake angle and fibre orientation on the bouncing back.

There is an increasing demand for sensors in extreme environments, i.e. high temperature and radiation environments, where conventional sensors lose their functionality and reliability because of the environmental impact. The dependence on electricity makes conventional sensor susceptible to extreme accident situation and demanding frequent maintenance which could be even more costly in those extreme environments. To overcome this problem, this thesis reports the development of a remote optically actuated and interrogated resonant sensor with a micro corner cube retroreflector (CCR) structure. The proposed sensor takes the advantage of MEMS scaling to enable optical actuation and remote interrogation. It does not rely on any local electrical power or electric elements therefore it is more resistant to high temperature and radiation impact. In this thesis, a micro paddle resonant sensor is theoretically shown to be able to get actuated without using electrical power or electric element. The remote actuation with optical method was analytically modelled and simulated. A simple and impact optical interrogation system is designed by combining the micro paddle resonator with a micro CCR structure which allows interrogating light source and detecting photodiode to be placed in the same place utilising the retroreflection of the CCR. The fabrication methods of the paddle mirror and micro CCR sidewalls were demonstrated respectively. Finally, a completed fabrication plan is provided.

To attend the growing global demand for energy, oil production—expected to grow in the foreseeable future-relies on the extraction from unconventional resources, such as deep deposits off the coast and ultra-deep water. These environments are contaminated with significant amounts of hydrogen sulphide, a by–product that promotes hydrogen absorp- tion and subsequent failure by sulphide stress cracking (SSC). The 17-4 PH—a stainless steel widely used for oilfield components—is susceptible to SSC, in spite of its favourable combination of properties. In this study, plasma–based treatments, often used to improve wear resistance, were identified as potential methods to increase the resistance to SSC. To evaluate it, the 17-4 PH was surface–modified by conventional and low–temperature plasma nitriding (LTPN) and submitted to standard SSC experiments. LTPN resulted in superior resistance to SSC compared to both unmodified and HTPN conditions, at- tributed to the formation of a nitrogen–rich layer comprising mixed iron nitrides (ε–Fe2-3N and γ’–Fe4N) and expanded martensite without precipitation of chromium nitrides. The protection provided by this structure was mainly due to the compressive residual stress induced by nitriding, combined with the superior resistance to localise corrosion and the reduced hydrogen uptake by the substrate.

In this study, an efficient expander and compressor are developed using Wankel engine concept for compressed air-electric hybrid vehicle to reduce the environmental impact of automotive industry. This research presents a new approach that integrates the 1D preliminary design using MATLAB software and three dimensional (3D) computational fluid dynamics (CFD) modelling using ANSYS®17·2 for more accurate prediction of the performance and flow dynamics at various crank angles, port configurations and locations to optimise the design of the Wankel expander and compressor. Therefore, investigations of Wankel expanders were carried out at various operating conditions to achieve a power output ranging from 1-25 kW. A novel two-stage Wankel expander was developed to achieve high efficiency and compactness design compared to the single-stage expander using the 3D CFD modelling. The study of Wankel compressor was carried out using two inlet ports and two outlet ports to investigate the performance of compressor with different sizes and ports' locations and size. Compressed air-electric hybrid system was developed to recover braking energy to produce compressed air that will be used to power the vehicle. Finally, a single-stage Wankel expander using two inlet ports and two outlet ports was manufactured, assembled and tested experimentally using compressed air.