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The rapidly increasing demand on power density levels of electric vehicle (EV) drive systems is pushing the boundaries of traction motor performance. Hairpin windings are becoming a popular option for EV motors due to their reduced DC losses and improved heat dissipation capability when compared to traditional random windings. In this paper, a comprehensive design approach of hairpin winding layouts is firstly presented. The flexibility and limitation of end-winding patterns is thoroughly investigated in terms of basic pin connections, special jumpers, transposition, parallel branches, terminal positions, phase shift, winding pitches as well as slot-pole combinations. To address the challenge of much reduced practical layout options with increased slot number per pole per phase, two novel hairpin winding designs are proposed. A 160kW, 18000rpm PM traction motor featuring the new winding layout with 54-slot, 6-pole is developed using a multidomain design platformwhich puts special focus on the conductor size optimization. The advantages of the designed motor are clearly revealed by comparison with the more traditional 48-slot, 8-pole counterpart. Finally, a corresponding stator prototype with the proposed hairpin winding is built to validate its manufacturability.

In this article, we describe the research and development of a 3 kV active rectifier for a 4 MW aerospace generator drive system demonstrator. The converter is fed by a multiphase high-speed/high-frequency permanent magnet generator. The main aim of the work is to demonstrate for the first time the feasibility of an MW-class generator system meeting future hybrid-electric propulsion requirements. A concept with multiple and isolated three-phase systems feeding different power buses is proposed to meet the availability requirements. Multiple converters (one for each three-phase system) are connected in series and/or in parallel to achieve the rated power and dc-link voltage. This article describes the key design concepts and the development and testing of the converter to meet the challenging application requirements. Reduced power tests are carried out on a full-scale 4 MW converter prototype, validating the proposed design. The work represents a step forward in terms of voltage, power, and output frequency with respect to the state-of-the-art.

Fringe analysis is a commonly used method to quantify soot nanostructures. However, the settings of the involved filters and their impact on the results are rarely addressed. In this study, the influence of the three filter parameters as well as two aspects of the image acquisition was assessed experimentally. For the analysis, a carbon black as well as one diesel engine and one gasoline direct injection (GDI) engine soot sample were used. Gaussian low-pass filter standard deviations larger 1.5 yielded only minor differences in fringe metrics. Standard deviations between 2.0 and 3.0 enabled realistic representation of fringes. A linear correlation was found between the white top-hat transformation disk size and all fringe analysis metrics. For realistic nanostructure representation, disk sizes of 5 px and 7 px are most suitable. Threshold values as calculated by Otsu's method generally yielded the best nanostructure representation. Any deviation distorted the extracted fringes and noticeably reduced their total number. Thus, consistent use of Otsu thresholds without alterations is advised. Deviating from the neutral electron microscope focus point by under- and over-focusing resulted in distinctive drops in both fringe lengths and Otsu thresholds. Consistent focusing with the help of fast Fourier transformations of the respective particles is vital for reliable results. The effect of reduced noise levels by repeated averaged images was found to be minor beyond the model of the camera used. The region of interest size correlated linearly with the number of extracted fringes, however, it did not affect the fringe metrics. For statistically reliable analysis, a minimum of 4000 fringes is suggested. The GDI sample exhibited the shortest fringes and the highest tortuosity. For diesel soot and carbon black, similar fringe lengths could be observed. The highest tortuosity was found for GDI soot, followed by diesel soot and carbon black.

High strength magnetic steel laminations are the invariable choice to achieve the power density demands of high speed electric machines required in the automotive industry. However, the cost competitive automobile market, favours the use of conventional materials. Consequently, in this paper, a high strength martensitic sleeve rotor configuration is identified as an ideal choice to maximize the use of conventional materials in a high speed synchronous reluctance (SynRel) machine. A 3.5 kW, 60 krpm high speed SynRel machine is designed for an electric assist turbocharger (EAT) to disclose the benefits of sleeve rotor configuration. The performance of the sleeve rotor is on par and superior to a SynRel machines employing high and low strength laminations respectively. Finally, a multiphysics optimization is performed to ascertain the superiority of sleeve rotor SynRel configuration. Based on this, the sleeve rotor produces 4.5% and 46.7% more torque than the SynRel machines using high and low strength laminations with conventional rotor configurations. Additionally, this is achieved with nearly 90% by volume of conventional rotor lamination.

Misfolding and aggregation of α-synuclein are specific features of Parkinson’s disease and other neurodegenerative diseases defined as synucleinopathies. Parkinson’s disease progression has been correlated with the formation and extracellular release of α-synuclein aggregates, as well as with their spread from neuron to neuron. Therapeutic interventions in the initial stages of Parkinson’s disease require a clear understanding of the mechanisms by which α-synuclein disrupts the physiological synaptic and plastic activity of the basal ganglia. For this reason, we identified two early time points to clarify how the intrastriatal injection of α-synuclein-preformed fibrils in rodents via retrograde transmission induces time-dependent electrophysiological and behavioural alterations. We found that intrastriatal α-synuclein-preformed fibrils perturb the firing rate of dopaminergic neurons in the substantia nigra pars compacta, while the discharge of putative GABAergic cells of the substantia nigra pars reticulata is unchanged. The α-synuclein-induced dysregulation of nigrostriatal function also impairs, in a time-dependent manner, the two main forms of striatal synaptic plasticity, long-term potentiation and long-term depression. We also observed an increased glutamatergic transmission measured as an augmented frequency of spontaneous excitatory synaptic currents. These changes in neuronal function in the substantia nigra pars compacta and striatum were observed before overt neuronal death occurred. In an additional set of experiments, we were able to rescue α-synuclein-induced alterations of motor function, striatal synaptic plasticity and increased spontaneous excitatory synaptic currents by subchronic treatment with l-DOPA, a precursor of dopamine widely used in the therapy of Parkinson’s disease, clearly demonstrating that a dysfunctional dopamine system plays a critical role in the early phases of the disease., Tozzi et al. show that intrastriatal injection of α-synuclein fibrils, modelling the early phase of Parkinson’s disease, alters motor behaviour and nigral and striatal neuron function in mice. These alterations can be rescued by l-DOPA, demonstrating the importance of the dopaminergic system in the early stages of Parkinson’s disease.

This article describes the underpinning research, development, construction, and testing of a 4-MW multithree phase generator designed for a hybrid-electric aircraft propulsion system demonstrator. The aim of the work is to demonstrate gravimetric power densities around 20 kW/kg, as required for multi-MW aircraft propulsion systems. The key design choices, development procedures, and tradeoffs, together with the experimental testing of this electrical machine connected to an active rectifier, are presented. A time-efficient analytical approach to the downselection of various machine configurations, geometrical variables, different active and passive materials, and different thermal management options is first presented. A detailed design approach based on the 3-D finite element analysis (FEA) is then presented for the final design. Reduced power tests are carried out on a full-scale 4-MW machine prototype, validating the proposed design. The experimental results are in good agreement with simulation and show significant progress in the field of high-power-density electrical machines at the targeted power rating.

This paper describes the methodology adopted for the development of electrical machines for hybrid propulsion systems (HPS) of aircrafts. A nominal power of 400 kW and a rotating speed of 12,000 rpm are the main specifications of the machine taken as reference. All the design steps, including the machine concept generation, the multi-physics numerical approach and the experimental evaluation of the performance are considered. Additionally, challenges encountered during the design process and the methods to overcome them are also presented. The technical failure observed during the testing of the prototype is being documented and the reasons which led to it are analyzed.

This paper describes the methodology adopted for the numerical thermal modelling of both submerged jets (single phase) and nebulized jets (multi-phase) used for the cooling of hairpin type end-windings. The work highlights the challenges arising when modelling discrete phases using computational fluidynamics (CFD) and proposes a setup for effectively capturing the physics whilst maintaining an acceptable level of computational cost of the simulations involving multi-phase cases. Additionally, a comparison of the cooling performance of the two strategies is carried out by observing the convective phenomena. Indeed, despite the overall lower fluid velocity achieved, the single-phase case shows an heat transfer rate double compared to the spray cooling and more uniform temperature distribution all over the winding surface thanks to the bigger level of penetration through the gaps in between the conductors.

In recent years, synchronous reluctance (Syn-Rel) machines are research hotspots in variable speed motor drives due to their robust rotor structure and wide constant power speed range (CPSR). More practically, when kVA limitation is considered, embedded permanent magnets (PMs) have been widely adopted in Syn-Rel rotors to further increase power density as well as power factor. In this paper, the authors have investigated the potential of PM-assisted Syn-Rel machine to be the next generation electrical propulsion motor topology for automotive application, with special attention put on a key geometric parameter, i.e., airgap length. In MTPA region, the influence of airgap length on different torque components has been analyzed in detail based on the frozen permeability method. In field weakening region, the variation trend of several key performance such as peak power, iron loss and torque ripple have been investigated along with airgap length. It is found that with specifically high level of electric and magnetic loading, there exists optimal value of airgap length to achieve high power density based on specific cooling and kVA limitation. Numerical FEA and experimental tests are associated to validate the conclusions.

In recent years, the development and characterization of new refrigerants with higher energetic efficiency have gained considerable interest [1], with a particular emphasis on the energetic performance of suitable replacements. Nanofluids have been proposed as possible alternative due to their role in enhancing the thermophysical proprieties of traditional refrigerants [2]. The comprehensive review in [2] suggests that thermal conductivity of nanofluid increases with temperature and volume concentration but it is dependent on nanoparticle size distribution; specific heat is also increased if nanoparticles are added to the refrigerant. As consequence, the improved heat transfer coefficients lead to COP improvements for the same cooling capacity. Recently, the addition of nanoparticles to the compressor oil from a refrigerator has been found to reduce the friction coefficient up to 90% [3]; this suggests that nanoparticles migrating to the lubricant oil can also contribute to improve efficiency and reliability of the system. Findings from the literature are however contradictory at times [2]; it is therefore necessary to further explore the benefits of using nanoparticles dispersed in refrigerants. The present work focuses on a quantitative analysis of the performance enhancement for a vapour-compression refrigeration system due to addition of aluminium oxide (Al2O3) nanoparticle to a commercially available refrigerant, tetrafluoroethane (R134a).

With the continuous growth of energy demand for the commercial transport sector, the market share of diesel vehicles is rising in several areas worldwide. Global demand for transport energy is therefore believed to be strongly skewed towards heavier fuels; particularly diesel. The strengthen emissions legislation is another issue facing the current generation of diesel engines; where there is an increasing concern with their high NOx and PM emissions. Dual-fuelling of diesel engines with natural gas (NG) stands as an attractive solution to reduce the dependence on diesel fuel and mitigate the harmful effects of diesel engines emissions. The main attractions of NG as a contributor to a more sustainable fuel market include its lower carbon content and relatively higher natural reserves, in addition to the renewable aspect of methane production from biogas. In dual-fuelling strategy, most of the engine power output is provided by the NG, while a pilot amount of diesel fuel is used as an ignition source for the NG-air mixture. While the concept is not new and it has been deliberated lengthily in the past two decades, several uncertainties still exist as relative to engine combustion, exhaust emissions, and practicality. The present contribution aims at critically reviewing part of the prevalent literature about NG-diesel dual-fuel engines; highlighting the concepts and challenges. Throughout this review, several topics are explored and evaluated based on research importance and maturity. The overview of these works indicates that research effort in this field could be broadly categorized into fuel delivery researches or charge composition studies; where each category is directly linked to either the NG or the pilot fuel. Following this, a roadmap for future research directions in the field is presented, to spot some potential topics for proceedings and continuation.

Copper leaching in diesel fuel and its impact on combustion and emission characteristics of a Direct Injection High Pressure Common Rail (DI HPCR) diesel engine was investigated. This work was performed using a single cylinder Ricardo Hydra research engine fitted with a cylinder head, piston assembly, and crankshaft from a production 2.2 L DI diesel engine. A fuel conditioning device consisting of a helicoidally shaped copper duct and electromagnetic coils powered from the battery was installed along the fuel line just before the high pressure pump. A diesel fuel with a copper content of less than 0.2 ppm was used. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed an increase of copper content to 1 ppm when fuel flowed through the conditioning device prior to the injection and returned from the engine back to the fuel tank. Copper leaching from the conditioning device was confirmed using a bespoke test rig. Combustion characteristics were analysed via post-processing pressure measurements, while an AVL Smoke Meter was used to monitor particulate emissions. A pilot plus main strategy was used to achieve a target Brake Mean Effect Pressure (BMEP) typical of medium load. Soot reduction in the range of 7–14% was measured when the device was connected to the fuel line, compared to the baseline. The initiation and early development of combustion was also investigated using an unstirred, quiescent combustion chamber with optical access. High-speed photography showed that ignition probability was enhanced in presence of the fuel conditioning device.

Recently, the synchronous reluctance machine limits have been pushed toward meeting the requirements of traction applications. A skilled electromagnetic architecture of a synchronous reluctance machine with the help of permanent magnets can push the limits of power density and speed range to that of traction applications, however, the mechanical integrity of the rotor can still be in question. A traction application means large rotor diameter and high rotational speed, two criteria that makes a challenging design, in particular, mechanically. In this paper, the multi-physics design steps of a permanent magnets assisted synchronous reluctance motor for automotive application, have been presented. Firstly, the electromagnetic design following the size and thermal aspects and constrains has been conducted. Secondly, methods to reduce the mechanical stress has been explored and a bridged mechanical design has been adapted. Finally, thermal analysis of the machine has been conducted to ensure the thermal limits have been satisfied.

High power density and high torque density are the fundamental requirements for electric machines used in traction application. The former is obtained by potentially increasing the speed of the machine while the latter by using high energy density rare earth magnets. Ferrite magnets are explored as a viable alternative to rare earth magnets which are relatively expensive and geographically concentrated. The paper is intended to bring out the current trend of electric machines used in electric vehicles (EVs) with due focus on permanent magnet assisted synchronous reluctance (PM-SynRel) machine. High power and high speed PM-SynRel machine with rare earth and ferrite magnets are designed and compared based on the requirements for a future electric commercial vehicles. The ratio of stack length, mass of magnet, total mass and inertia of rare earth machine in comparison to ferrite PM-SynRel is found to be 0.72, 0.42, 0.72 and 0.32, respectively. Based on these, the rare earth based machine is found to have high power density, torque density and also utilizes lesser volume of magnets but PM-SynRel with ferrite is getting closer.

This paper presents a computational fluid dynamics conjugate heat transfer analysis of internal and external cooling paths for a hollow high-speed permanent magnet rotor. Extracting magnet losses from high-speed permanent magnet rotors is challenging, due to the thermal limits of magnets and composite magnet retention sleeves. This paper proposes the use of internal and external air-cooling paths through the hollow rotor and airgap, respectively. Component temperatures with respect to these cooling paths are investigated. The balance of interactions between the internal, external and component temperatures is complex and is best solved using computational fluid dynamics. The passing of cooling air through and outside the rotor improves the cooling of components. However, there are limits, as forcing progressively more air through the airgap is shown to eventually cause a net heating of the rotor, due to fluid viscous heating effects. Differences in modelling temperature dependent fluid properties is explored and shown to make an important difference when designing machines to maximize their material thermal capabilities.

This paper describes the thermal-mechanical characterisation methodology for the bearing chambers of a high-speed (32,000 rpm) electrical starter/generator [1]; presenting a low cost analysis approach and design guideline for future machines. The methodology includes the estimation of the friction losses, overall thermal properties, bearing contact resistances and heat transfer coefficients. An analysis of the heat paths within the chambers, as well as within the whole rotor was carried out, allowing to quantify the heat extracted by the lubricant. The model was developed as part of the thermal-mechanical design of a specific starter/generator but the modelling approach presented within this paper is applicable to any high speed application

Formation of soot is a known phenomenon for diesel engines, however, only recently emerged for gasoline engines with the introduction of direct injection systems. Soot-in-oil samples from a three-cylinder turbo-charged gasoline direct injection (GDI) engine have been analysed. The samples were collected from the oil sump after periods of use in predominantly urban driving conditions with start-stop mode activated. Thermogravimetric analysis (TGA) was performed to measure the soot content in the drained oils. Soot deposition rates were similar to previously reported rates for diesel engines, i.e. 1 wt% per 15,000 km, thus indicating a similar importance. Morphology was assessed by transmission electron microscopy (TEM). Images showed fractal agglomerates comprising multiple primary particles with characteristic core-shell nanostructure. Furthermore, large amorphous structures were observed. Primary particle sizes ranged from 12 to 55 nm, with a mean diameter of 30 nm and mode at 31 nm. Particle agglomerates were measured by nanoparticle tracking analysis (NTA). The agglomerates were found to range between 42 and 475 nm, with a mean size of 132 nm and mode at 100 nm. The distribution was shifted towards larger sizes with a minor concentration of very large agglomerates observed around 382 nm. While deposition rate and agglomerate morphology were similar to diesel engines, distinctive amorphous carbon and smaller particles were observed. Hence, existing knowledge for diesel applications might not be directly transferrable.

More-electric aircraft (MEA) has become a dominant trend for modern aircraft. On-board MEA, many functions, which are conventionally driven by pneumatic and hydraulic power, are replaced with electrical subsystems. Starting aircraft engines with an electric motor instead of using pneumatic power from the auxiliary power unit is one of the major characteristics of future aircraft. This paper presents the development of a novel electric starter–generator system for aircraft applications. This paper describes the main achievements of the AEGART (EU CleanSky Project) project in the key areas, including electric machines, power electronic converters, thermal management, and overall system control design. The developed prototype has been tested successfully, and the test results are presented in this paper.

The size and morphology of soot particles and agglomerates extracted from lubricating oil drawn from the sump of a diesel engine have been investigated and compared using Transmission Electron Microscopy (TEM) and Nanoparticle Tracking Analysis (NTA). Samples were prepared for electron microscopy imaging by both centrifugation and solvent extraction to investigate the impact of these procedures on the morphological characteristics, such as skeleton length and width and circularity, of the obtained soot. It was shown that centrifugation increases the extent of agglomeration within the sample, with 15% of the agglomerates above 200 nm compared to only 11% in the solvent extracted soot. It was also observed that the width of centrifugation extracted soot was typically 10 nm to 20 nm larger than that of solvent extracted soot, suggesting that centrifugation forces the individual agglomerate chains together. Moreover, centrifugation fails to extract a large percentage of particles below 50 nm, with only 4% of the agglomerates smaller than 50 nm in the centrifugation extracted soot, whereas agglomerates in this size range accounted for 19 % using solvent extraction. As TEM represents a comparatively time and cost expensive characterisation tool, unsuitable for high throughput testing required by industry, NTA was explored as a low cost, rapid alternative method for measuring particle size. It was found that results generated by NTA, within the limits of detection, correlated well with those obtained using TEM. This correlative electron microscopy and light scattering approach was further used to appraise the morphological characteristics of two commercial sources of carbon black (CB), enabling the selection of the most suitable soot surrogate, essential for the further development of oils with optimised functional properties.

© 2015 IEEE. This paper proposes a novel solid rotor topology for an interior permanent magnet (IPM) machine, adopted in this case for an aircraft starter-generator design. The key challenge in the design is to satisfy two operating conditions that are a high torque at start and a high speed at cruise. Conventional IPM topologies that are highly capable of extended field weakening are found to be limited at high speed due to structural constraints associated with the rotor material. To adopt the IPM concept for high-speed operation, it is proposed to adopt a rotor constructed from semimagnetic stainless steel, which has a higher yield strength than laminated silicon steel. To maintain minimal stress levels and also minimize the resultant eddy current losses due to the lack of laminations, different approaches are considered and studied. Finally, to achieve a better tradeoff between the structural and electromagnetic constraints, a novel slitted approach is implemented on the rotor. The proposed rotor topology is verified using electromagnetic, static structural, and dynamic structural finite-element analyses. An experiment is performed to confirm the feasibility of the proposed rotor. It is shown that the proposed solid rotor concept for an IPM fulfils the design requirements while satisfying the structural, thermal, and magnetic limitations.

Two 3-D six-hole transparent enlarged model injector have been manufactured with full optical access; both were 15 times larger than the real size, but one had a length-to-diameter ratio twice as the second one. The working fluid was water and aqueous solutions of glycerol circulating through the nozzle injector under steadystate flow conditions at different flow rates, pressures and needle lift positions. Real-time in-nozzle flow visualisations were obtained using a high speed video recorder which allowed determination of in-nozzle flow patterns, in particular, formation, dynamics and the development of cavitation. Simultaneous imaging of the flow inside the nozzle injector showed that reducing the needle lift would suppress the cavitation intensity in both models especially during early stage of cavitation causing a delay on its onset from a CN≈1.1 at full lift to CN=1.9 at 25% of the full. The main noticeable effect of L/D was found to be at the exit of the nozzles where different types of in-nozzle flow would be experienced due to different length of the nozzles with larger L/D having a more developed and stable cavitating flow and is expected to affect spray outside the nozzles. The effect of viscosity was only evident during early stage of cavitation with a delay on the onset of the cavitation and a less intense cavitation with blends at higher viscosities. The results also showed that an increase in temperature had the effect of enhancing cavitation due to lower viscosity and weaker molecular bounding.