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A Cascade H Bridge (CHB) is evaluated for both electric vehicle motor traction control and off-vehicle charging against the PowerElectronicsUK Automotive Challenge for cost and mass for the year 2035. By combining the power electronics with batteries using low-voltage MOSFET transistors in a series cascade arrangement the cost and mass targets could be met 12 years earlier (in 2023 and 20 times lighter if an application specific integrated circuit (ASIC) is used. \ud \ud A 200kW peak reference car was used to evaluate cost and mass benefits using four different topologies of power electronics. \ud \ud Vehicle installation is shown to be simplified as only passive cooling is required removing the need for liquid cooling systems and the arrangement is inherently safe; no high voltages are present when the vehicle is stationary. The inherently higher efficiency of CHB increases vehicle range. \ud \ud The converter with integrated batteries can also behave as an integrated on-board battery charger delivering additional off-vehicle benefits by removing the need for costly external chargers.

Ground heat exchangers are surrounded by grout material, making it one of the most important components in geothermal energy applications since it significantly affects the system's thermal performance. The current study reviews the different types of grout materials and compares their thermophysical properties. The most critical parameter is the grout's thermal conductivity in which it always presents a proportional relation with the system's efficiency. Numerous factors are involved in this review to ascertain theier impact on the grouts’ performance such as flowability, shrinkage, moisture content, freezing, heat capacity, strength, permeability, solubility and thermal imbalance. The different grouts compared are bentonite, cement, sand, graphite, controlled low-strength material, dolomite, and phase change materials. The literature shows that phase change materials are the best choices of grouting since they can provide high storage capacity, stability and temperature uniformity. The major problem of such materials is their low thermal conductivity. Thus, it is recommended to use composite phase change materials to enhance their thermal conductivity and increase the storage/retrieval rate.

Due to low system inertia in microgrids, frequencies may vary rapidly from the nominal value, leading to the complete blackout of the system unless there is an adequate spinning reserve available for balancing the supply with the demand load. This issue of instability in microgrids under islanded operation has attracted particular attention recently. A diesel generator is considered to be an ideal spinning reserve to provide back-up power to the load along with the renewable energy source in islanded system. However, the high maintenance cost and CO2 emissions of diesel generator are detrimental factors which have inspired searches for more cost effective and cleaner technologies. The integration of an energy storage system (ESS) in islanded system along with generator not only reduces generator maintenance costs but also reduces the CO2 emissions by limiting its operating hours. This paper proposes an islanded PV hybrid microgrid system (PVHMS) utilizing flywheel energy storage systems (FESS) as an alternative to battery technology to support the PV system and meet the peak demand of a small residential town with 100 dwellings. The diesel generator is used in the islanded system as a spinning reserve to maintain the stability of the islanded system when the PV system and flywheel storage cannot meet the load demand. Results of analysis of such a system demonstrate that flywheel energy storage technology of appropriate size offers a viable solution to support the operation of the standalone PV system. Furthermore, the reduction in CO2 emissions and fuel consumption has been quantified as compared with the case with flywheel energy storage systems which means the diesel generator but always be operating.

This paper presents a new system that incorporates the CO2-based transcritical Rankine cycle with a geothermal condenser. The innovation studied in the current proposed system is the use of a shallow ground heat exchanger to activate a ground-cooled condenser instead of an air-cooled one in a power cycle. This combination is very beneficial for power generation, especially in summer because the ground is more effective than the ambient air in extracting heat from the working fluid passing through the condenser due to its lower temperature. Thus, for the same amount of heat added to the cycle, more power could be produced due to the increase in pressure difference between the gas heater and condenser. Consequently, the operating cost of the system will be reduced. This parametric study covers a wide range of heat source applications with gas temperature and mass flow rate being varied between 500 and 1500 °C and 100–350 kg/hr respectively. The objective is to generate the maximum possible power while minimizing the sizes of the heat exchangers. The results show that the best parameters to be controlled are the turbine inlet temperature and CO2 pipe diameter. The incorporation of ground-cooled condenser significantly enhanced the cycle’s performance in which the net output power could be increased by ~ 30% compared to the conventional Rankine cycle. This enhancement mainly depends on the ground’s temperature since it directly changes the condensation temperature and hence affects the working fluid expansion.

Flywheel energy storage systems (FESS) are one of the earliest forms of energy storage technologies with several benefits of long service time, high power density, low maintenance, and insensitivity to environmental conditions being important areas of research in recent years. This paper focusses on the electrical machine and power electronics, an important part of a flywheel system, the electrical machine rotating with the flywheel inertia in order to perform charge-discharge cycles. The type of machine used in the electrical drive plays an important role in the characteristics governing electrical losses as well as standby losses. Permanent magnet synchronous machine (PMSM) and induction machines (IM) are the two most common types of electric machines used in FESS applications where the latter has negligible standby losses due to its lower rotor magnetic field until energised by the stator. This paper describes research in which the operational and standby losses of a squirrel-cage induction machine-based flywheel storage system (SCIM-FESS) are modelled as a system developed in MATLAB/Simulink environment inclusive of the control system for the power electronics converters. Using the proposed control algorithm and in-depth analysis of the system losses, a detailed assessment of the dynamic performance of the SCIM-FESS is performed for different states of charging, discharging, and standby modes. The results of the analysis show that, in presence of system losses including aerodynamic and bearing friction losses, the SCIM-FESS has satisfactory characteristics in energy regulation and dynamic response during load torque variations. The compliance of FESS and its conversion between the generating and motoring mode within milliseconds show the responsiveness of the proposed control system.

The performance of an automotive turbocharger centrifugal compressor has been studied by developing a comprehensive one-dimensional (1D) code as verified through experimental results and a three-dimensional (3D) model. For 1D analysis, the fluid stream in compressor is modeled using governing gas dynamics equations and the loss mechanisms have been investigated and added to the numerical model. The objective is to develop and offer a 1D model, which considers all loss mechanisms, slip, blockage and also predicts the surge margin and choke conditions. The model captures all features from inlet duct through to volute discharge. Performance characteristics are obtained using preliminary geometry and the blade characteristics. A 3D numerical model was also created and a viscous solver used for investigating the compressor characteristics. The numerical model results show good agreement with experimental data through compressor pressure ratio and efficiency. The effect of the main compressor dimensions on compressor performance has been investigated for wide operating range and the portions of each loss mechanism in the impeller. Higher pressure ratio is achievable by increasing impeller blade height at outlet, impeller blade angle on inlet, diffuser outlet diameter and by decreasing impeller shroud diameter at inlet and blade angle at outlet. These changes may cause unfavorable consequences such as a lower surge margin or shorter operating range, which should be compromised with favorable changes. At lower rotational speeds, impeller skin friction mainly impacts the performance and at higher rotational speeds, impeller diffusion, blade loading and recirculation losses are more important. The results allow the share of each loss mechanism to be quantified for different mass flow rates and rotational speed, shedding new light on which losses are most important for which conditions. For a turbocharger, which must operate over a wide range of conditions, these results bring new insight to engineers seeking to optimize the compressor design as part of an internal combustion engine system.

Flywheels, one of the earliest forms of energy storage, could play a significant role in the transformation of the electrical power system into one which is fully sustainable yet low cost. This article describes the major components that make up a flywheel configured for electrical storage and why current commercially available designs of steel and composite rotor families coexist. In the process, design drivers, based on fundamentals are explained in a clear and simple manner inclusive of approaches to safety. The robust characteristics of flywheels deem them highly suitable for applications requiring fast response and high daily cycles, a need that is growing as grid inertia reduces. Lithium Ion batteries are currently the technology of choice for fast response but suffer from limited cycle and calendar life. This can be mitigated by having sufficient energy capacity to limit depth of discharge during short duration cycles whilst using this capacity to earn revenue for provision of other services. Now, as other mechanical, thermal to electric and renewable fuel based storage technologies develop, these will provide storage at a lower cost, greater duration and in a more sustainable way than Lithium Ion. However, the need for fast response storage will remain and steel flywheels are well placed to provide this given potential for low power cost and their sustainability credentials. In order to obtain cost estimates for flywheels in volume production, the cost of the power and storage elements were separated out with costs for each based on similar technologies in volume production. These indicate significantly lower costs than given for current commercially available flywheels, none of which are in volume production relative to Lithium Ion. Finally, some areas of research with potential to improve performance are described but, to be worthwhile, these developments must not lead to increased costs.

This paper presents a review of hydrogen production systems using geothermal energy, showing the importance and potential of this technology in addition to the main obstacles facing this domain. The effect of several parameters was taken into consideration, such as geothermal fluid temperature, water electrolysis temperature, working fluid, and type of power cycle. The different types of geothermal power plants were also compared, namely, flash, binary, flash-binary, recuperative, regenerative, and organic Rankine flash cycles. This study covers a wide range of investigations regarding hydrogen production rate, hydrogen production cost, energetic efficiency, exergetic efficiency, exergetic cost, and electricity generated. Hydrogen production rate is one of the most important mentioned parameters in which it was found to vary from 5.439 kg/h to 13958 kg/h. Multigeneration systems have shown great potential to enhance the overall system’s efficiency, leading to reduced production costs. The integration of another energy source was found to be interesting in geothermal-driven hydrogen production systems. This would promote the adoption of multigeneration system as well as increasing the geothermal fluid’s temperature before entering the power cycle.

World energy consumption has increased significantly in the last decade and for this reason several energy management strategies are currently under investigation to accommodate this high demand. In this frame, the current paper presents a review of the advances of district systems (DSs) which offers a contribution to the mission to reduce the environmental and economic impact of energy consumption. The aim of the study is to examine the potential of these systems and their ability to cope with the requirements of energy demands. Additionally, the paper reviews several optimization strategies including poly-generation, cogeneration and energy storage that could be adopted to upgrade the performance of DSs. Furthermore, the paper discusses the main obstacles facing the development of this domain and proposes some suggestions to encourage adoption of the district approach.

This paper describes the authors’ investigation into deploying durable, low cost electric flywheel technology on rail vehicles by means of simulation. Diesel engines currently power trains on non-electrified lines, over half the UK rail network, so the Rail Safety and Standards Board (RSSB) commissioned research to devise efficiency improvements. Substantial benefits in the form of diesel traction energy saving and braking energy recovery were calculated, amounting to 43% for regional passenger services. Further, the flywheel technology is traction-type independent: it could be key to unlocking discontinuous electrification or to improve the effectiveness of any prime mover. A follow-on hardware demonstration project has just commenced.

Mechanical energy storage systems are among the most efficient and sustainable energy storage systems. There are three main types of mechanical energy storage systems; flywheel, pumped hydro and compressed air. This paper discusses the recent advances of mechanical energy storage systems coupled with wind and solar energies in terms of their utilization. It also discusses the advances and evolution in each type and compares them in terms of performance, capacity, response and utilizations. The reviewed studies exhibit all parameters that affect the performance of each storage type in which the configuration of the system has the major effective role. Choosing the suitable mechanical storage type depends on the requirements of each application such as using the flywheel for short duration applications. If long duration is needed, then it is preferred to use either pumped hydro or compressed air storage systems, knowing that the former has higher efficiency while the latter provides a faster start up. For the sake of the environment, it is recommended to use the adiabatic or isothermal compressed air storage. In all cases that combine MESSs with solar or wind energy, the series connection is preferred in order to provide stability and better control strategy.

For stable operation of the electrical grid, it is vital to maintain a balance between demand and supply of electrical power. Imbalance at any instant between consumption and generation causes voltage and frequency instability. Intermittent generation (wind and solar) in power systems is more likely to cause such imbalances hence the existence of frequency and voltage variations. To address stability issues due to integration of intermittent renewable sources into the grid, a storage device is required which can quickly respond to the power fluctuations. A Flywheel Energy Storage System (FESS) has the capability to respond within a sub-second timescale and is able to address the problems caused by power variations. The performance of FESS is highly dependent on the type of motor/generator (MG) set which is the key component generating or absorbing power from grid. The three main types of electrical machines used in FESS applications are synchronous machine (SM), induction machine (IM) and the switched reluctance machine (SRM). SRM is less commonly used due to high current ripples and complex torque control [1]. SM is used for high speed applications due to its high efficiency and IM is used for high power applications due to its rough construction. This research focuses on the comparison of synchronous and induction machines used in flywheel energy storage systems for microgrid applications [2]. The operation and controlling schemes of each electrical machine has been described as used in the analysis made in the MATLAB/Simulink environment

Recent flywheel development has allowed high power and energy storage levels to be demonstrated driven by the needs for energy storage in transport and ground power applications. This article starts with a brief historical overview of flywheels, moving to the specifics of rotor design, the main subject addressed. Following the elastic stress analysis for rotating isotropic disks, this is extended to orthotropic disks, as needed for treatment of filament wound composite constructions. A performance comparison is given for composites verses metals, quantified according to stated assumptions. Finally, important issues concerning composite flywheel constructions are discussed.

Energy storage systems (ESS) are key elements that can be used to improve electrical system efficiency by contributing to balance of supply and demand. They provide a means for enhancing the power quality and stability of electrical systems. They can enhance electrical system flexibility by mitigating supply intermittency, which has recently become problematic, due to the increased penetration of renewable generation. Flywheel energy storage systems (FESS) are a technology in which there is gathering interest due to a number of advantages offered over other storage solutions. These technical qualities attributed to flywheels include high power density, low environmental impact, long operational life, high round-trip efficiency and high cycle life. Furthermore, when configured in banks, they can store MJ levels of energy without any upper limit. Flywheels configured for grid connected operation are systems comprising of a mechanical part, the flywheel rotor, bearings and casings, and the electric drive part, inclusive of motor-generator (MG) and power electronics. This contribution focusses on the modelling and simulation of a high inertia FESS for energy storage applications which has the potential for use in the residential sector in more challenging situations, a subject area in which there are few publications. The type of electrical machine employed is a permanent magnet synchronous motor (PMSM) and this, along with the power electronics drive, is simulated in the MATLAB/Simulink environment. A brief description of the flywheel structure and applications are given as a means of providing context for the electrical modelling and simulation reported. The simulated results show that the system run-down losses are 5% per hour, with overall roundtrip efficiency of 88%. The flywheel speed and energy storage pattern comply with the torque variations, whilst the DC-bus voltage remains constant and stable within ±3% of the rated voltage, regardless of load fluctuations.

There is a critical lack of affordable transport services linking villages to markets, healthcare and other facilities in rural areas of sub-Saharan Africa, which significantly restrains rural development. A key factor is the severe constraint on profitability of services due to the high operating costs of conventional vehicles operating at relatively low speeds on rural roads. This paper argues that there is a need to consider lower-speed alternatives based on motorcycles. It shows that motorcycle-based vehicles such as trailers and three-wheelers can carry loads up to 1 t on rural roads when geared down to an appropriate speed. The operating costs of these vehicles are shown to be around half those of conventional vehicles, greatly increasing the potential for setting up profitable transport services. Further development is needed to show that motorcycle-based vehicles can be used safely and profitably to help rural people improve their livelihoods and facilitate rural development.

Energy storage devices are an essential part of hybrid and electric vehicles. The most commonly used ones are batteries, ultra capacitors and high speed flywheels. Among these, the flywheel is the only device that keeps the energy stored in the same form as the moving vehicle, i.e. mechanical energy. In order to connect the flywheel with the vehicle drive line, a suitable means is needed which would allow the flywheel to vary its speed continuously, in other words a continuously variable transmission (CVT) is needed. To improve the efficiency and speed ratio range of the variators, a power spilt CVT (PSCVT) can be employed. This paper discusses the kinematics of PSCVT used to connect the flywheel to the driveline. A methodology describing the characteristic equations of speed ratio, power flow and efficiency of the PSCVT for various types including power recirculating and multi regime in both directions of power flow has been presented. An example of a PSCVT for a flywheel energy storage system (FESS) is computed using the derived equations and the results compared.

The provision of affordable electrical power in off-grid rural areas of developing countries is a major challenge but a vital element in the battle to reduce poverty. In response to this need, the SCORE project objective was to integrate a novel technology, thermo-acoustics, into a domestic cooking stove in order to produce an adequate level of electricity supply for families in developing countries whilst also providing efficient cooking. The unit is aimed at the majority of poorer families in developing countries that do not have access to electricity and have little hope of being connected to grid electricity in the near future. The electrical generation function is a vital driver in the adoption of low emission stoves which significantly reduce health problems from smoke inhalation. This paper describes the design of the cooking part of the stove developed within the framework of the project. Within the wood burning stove, heat released by combustion is first transferred to a thermo-acoustic engine to generate electricity, and then to the cooking part. The paper describes the development of the design and construction of the stove to meet the above objectives. This has been progressed through extensive testing of prototype stoves and also through modelling of the heat transfer within the combustion chamber and also for the cooking part of the stove. The paper presents and compares the results from the test programme and heat transfer modelling and shows how the results are being used to achieve a stove design with an acceptable level of performance. It then concludes with a discussion of how this design might be produced in developing countries.

Nearly a quarter of the world’s population has no access to electricity and nearly half cook with biomass or coal. Over the past 30 years there have been several initiatives to design and introduce appropriate, renewable energy technologies for household energy supply. However, few of these have been successful in terms of significant penetration and long-term sustainability. A new initiative, the SCORE project, was launched in 2007 with the objective of producing a clean biomass cook stove which also incorporates a thermo-acoustic engine which converts some of the heat into electricity. It was vital to determine the technical requirements of this new device as a pre-requisite to engineering development particularly in the two candidate countries where this new technology was to be trialled: Nepal and Uganda. Accurate data could not be sourced in the open literature and therefore studies were commissioned in order to obtain the relevant data. The data obtained are of significant value for any development projects involving the provision of small-scale off-grid electrical power and heat for cooking. A major purpose of the paper is hence to quantify current cooking and lighting habits in order to clarify some of the socio-economic issues that are important to the technical design of cooking and lighting systems.

A design of the thermo-acoustic engine to combustion interface of an electrically generating clean cookstove is presented. Social surveys carried out by the SCORE project have indicated that adding electrical generation to a clean cookstove should increase their uptake considerably above the current 8% level (outside China) as electricity is perceived as high value and so wanted by the communities. This work discusses the development process, using elements of the formal design methodology BS 7000 to design a mass-producible, easy-to-manufacture, low-cost cooking stove that uses a thermo-acoustic engine to produce electricity whilst cooking. The iterative design process is discussed with analyses made of predicted cost and performance at each iteration and compared with the targets set from social surveys. With currently available technology and suitable investment in tooling and production facilities, estimated production costs are £100. An independent audit by engineers and cost estimators from a large international blue chip company made a prediction of £150. At this stage of the design, this is considered a quite good correlation. Proposals for bringing this cost down to £60 are made. To obtain lower costs would require more research. SCORE market evaluations indicate that at the upper-cost target of £60 (2007 prices), 60 million people would afford the stove. A wood-burning Score-Stove™2 prototype successfully developed 22.7 W of electricity based on the presented planar thermo-acoustic engine design, indicating that the new Score-Stove™2 design may have the potential, when manufactured in volume, to meet the social and cooking requirements of rural people in developing countries.

This paper describes a new experimental method for measuring stator heat transfer in a rotor-stator disc system using an electrical heater array. The system is partially blocked at the periphery, with radial outflow of rotor-pumped air from an inlet at stator centre. The aim is to improve thermal performance prediction for air-cooled disc type electrical machines. Local Nusselt numbers were measured for 0.6 < r / R < 1 at three non-dimensional gap ratios G = g / R = (0.0106, 0.0212, 0.0297) and rotational Reynolds numbers 3.7 e 4 (is less than or equal to) Re (is less than or equal to) 5.6 e 5. Transition at the stator is observed to occur at Re > 3 e 5 for all gap ratios. Increased Nusselt numbers at the periphery are observed for all Re and G because of the ingress of ambient air along the stator due to the rotor pumping effect.

Accurate thermal analysis of axial flux permanent magnet (AFPM) machines is crucial in predicting maximum power output. Stator convective heat transfer is one of the most important and least investigated heat transfer mechanisms and is the focus of this paper. Experimental measurements were undertaken using a thin-film electrical heating method, providing radially resolved steady state heat transfer data from an experimental rotor-stator system designed as a geometric mockup of a through-flow ventilated AFPM machine. The measurements are compared with computational fluid dynamics (CFD) simulations using both 2-D axisymmetric and 3-D models. These were found to give a conservative estimate of heat transfer, with inaccuracies near the edge and in the transitional flow regime. Predicted stator heat transfer was found to be relatively insensitive to the choice of turbulence model used in the CFD simulations. © 2011 IEEE.

There are different types of energy storage devices which are used in today’s hybrid and electric vehicles. Batteries, ultra capacitors and high speed flywheels are the most commonly used ones. While batteries and supercapacitors store energy in the form of electric energy, the flywheel (FW) is the only device that keeps the energy stored in the original form of mechanical energy the same as the moving vehicle. The flywheel needs to be coupled to the driveshaft of the vehicle in a manner which allows it to vary its speed independently of the moving vehicle in order to vary its energy content. In other words a continuously variable transmission (CVT) is needed. The common mechanical variators used in automotive applications, namely the rolling traction drives and the belt drives, have the disadvantage that their speed ratio range defined as the maximum to minimum speed ratio is generally not sufficient for flywheel energy storage system (FESS). One of the ways to improve the ratio range is by using a dual mode transmission, where the ratio coverage of the variator is exploited twice. This paper presents the fundamental kinematics of such a transmission including its variants. The equations of speed ratio, power flow and efficiency are derived for a variator only transmission and a power split CVT (PSCVT) used in dual mode and the results compared.

Hydropower is a proven renewable energy resource and future expansion potential exists in smaller-scale, low-head sites. A novel approach to low-head hydropower at run-of-river and tidal estuary sites is to include an intermediate air transmission stage. Water is made to flow through a siphon, rather than a conventional water turbine, and at the top of the siphon the pressure is sub-atmospheric and air is entrained into the water. The siphon forms a novel, hydraulically powered vacuum pump or ‘hydraulic air pump’ (HAP). Air is pumped by the HAP through a separate air turbine and generator. This arrangement offers dramatic increases in turbine-generator speed and allows better control and matching of components and lifecycle cost reductions due to reduced maintenance costs and the use of smaller rotating machines. This study builds on previous work on such systems by showing why the pumping process can be treated as isothermal. Also, initial test results with a small siphon are presented and compared to existing models. These show a discrepancy between predicted and measured pressure ratios and therefore an overprediction of efficiency and power output using simple mathematical models.

The principal task of the engine is to convert chemical energy into kinetic energy and then replace the various losses. So a car, which exists primarily to provide personal mobility, can be regarded technically as a kinetic energy system, above all else. This examination by Hy Kinesys and the City University of London (UK) identifies a more efficient way to provide regenerative braking and finds a more cost-effective way to provide acceleration without requiring the engine to provide most of the accelerative power.

This paper describes the development of a high-power high-speed eddy current dynamometer for turbocharger turbine research. Turbochargers are present in virtually all automotive diesel engines and it is essential to determine the characteristics of the turbine and compressor for inclusion into the engine model. Accurate measurement of the turbocharger turbine torque forms a vital part of this process. Earlier developments of dynamometers for this purpose are summarized and their limitations commented upon. The paper then describes the principle behind a new permanent magnet disc-type eddy current dynamometer including the relevant electromagnetic theory and analysis. The overall performance is given together with the results of an uncertainly analysis; a wide load range of 1.7-62.2 kW has been demonstrated at 60 000 r/min, and it allows characterization of turbine performance over the entire operating range, including the ability to measure unsteady torque.

Flywheel energy storage devices may be coupled to mechanical transmissions for braking energy recovery and the provision of additional power for acceleration in hybrid vehicles. Power transmission across a continuous range of speed ratios is necessary. The flywheel size and depth-of-discharge must be chosen for a particular application, and this has a direct effect on transmission efficiency, required gearing ratios and mass of components. Optimisation of these parameters requires a fundamental understanding of this interaction, which has not previously been investigated and reported. To address this, the current paper presents a new method of analysing mechanical flywheel systems. A simple algebraic analysis can be used to specify flywheel system parameters for any regenerative braking application where the flywheel is used to provide initial acceleration of the vehicle from stationary. This has been applied to systems using geared transmissions with continuous speed variation achieved through sliding contact in clutch and brake components. The results of the analysis highlight how the optimum selection of flywheel depth-of-discharge must achieve a balance between high transmission efficiency and low system mass. This is illustrated for a passenger car application, allowing a full assessment of system performance and the specification of appropriate design parameters.

Battery electric vehicles are crucial to the reduction in the dependence on fossil fuels and for moving towards a zero-emission transport system. Although battery electric vehicle technology has been rapidly improving, the limited driving range and the high cost are significant impediments to the popularity of electric vehicles. The battery is the main element which affects the range and the cost of the vehicle. The batteries can provide either high power or high energy but not both. Hybridisation of the energy source is one of the methods to improve the energy efficiency of the vehicle, which involves combining a high-energy battery with a high-power source. High-speed flywheels have attractive properties and low-cost potential which makes them excellent secondary energy storage devices to be used in hybrid and electric vehicles. They are utilised to load the battery to a level so as to protect it from peak loads and to enhance its capacity and life. The flywheel is coupled to the drive line with a continuously variable transmission. This paper presents the optimal energy management strategy for a mechanically connected flywheel-assisted battery electric vehicle powertrain. The optimisation problem is complex because of factors such as the small storage capacity of the flywheel, the kinematic constraints and the slipping of clutches. Dynamic programming is used to calculate the optimal control strategy for torque distribution during operation in real-world driving cycles. The results show significant potential for reduction in the energy consumption in extra-urban and highway cycles, while reducing the peak battery loads during all cycles. The results give a benchmark of the energy-saving potential for such a powertrain and insights into how a real suboptimal controller can be designed.

The development of battery electric vehicles (BEV) must continue since this can lead us towards a zero emission transport system. There has been an advent of the production BEVs in recent years; however their low range and high cost still remain the two important drawbacks. The battery is the element which strongly affects the cost and range of the BEV. The batteries offer either high specific power or high specific energy but not both. To provide the BEVs with the characteristic to compete with conventional vehicles it is beneficial to hybridize the energy storage combining a high energy battery with a high power source. This shields the battery from peak currents and improves its capacity and life. There are various devices which could qualify as a secondary storage system for the BEV such as high power battery, supercapacitor and high speed flywheel (FW). This paper aims to review a specific type of hybridisation of energy storage which combines batteries and high speed flywheels. The flywheel has been used as a secondary energy system in BEVs from the early 1970s when the oil crises triggered an interest in BEVs. Since the last decade the interest in flywheels has strengthened and their application in the kinetic energy recovery system (KERS) in Formula 1 has further bolstered the case for flywheels. With a number of automotive manufacturers getting involved in developing flywheels for road applications, the authors believe commercial flywheel based powertrains are likely to be seen in the near future. It is hence timely to produce a review of research and development in the area of flywheel assisted BEVs.

The flow through rotating orifices is of interest to the designer of machines incorporating such features. The designer often requires a set of correlations which can be used to check out preliminary designs and converge on a solution prior to attempting detailed and expansive analysis. The correlations given in this paper are based on the incidence angle, i, of the flow into the orifice and they allow the discharge coefficient for rotating orifices to be estimated for as many conditions and geometries as possible. The approach adopted is to group the parameters that affect the discharge coefficient to i = 0° (Reynolds number, orifice chamfer and radius, L/d ratio, pressure ratio, and pumping effect) and i ≠ 0° (rotation of the disc, preswirl, cross-flow, and the angle of inclination of the orifice). The effect of each parameter on the discharge coefficient can easily be observed when using this method. Furthermore, the method can predict the discharge coefficient for systems that have various parameters that are combined together. There is a good agreement between the correlations and the experimental results and the available data on rotating orifices in the open literature. The correlations also agree with various combinations run in computational fluid dynamics (CFD). The approach adopted in this paper, which is based on the incidence angle, can assist designers to find the combination of geometric and flow parameters that gives the best discharge coefficient for rotating orifices.

This paper reports on the design, fabrication, and testing of an axial-flux permanent magnet electromagnetic generator. The generator comprises a polymer rotor with embedded permanent magnets sandwiched between two silicon stators with electroplated planar coils. Finite element simulations have been carried out using ANSYS to determine the effects on performance of design parameters such as the number of layers in the stator coils, and the rotor-stator gap. The effect of including soft magnetic pole pieces on the stators has also been studied. A prototype device with a diameter of 7.5 mm has been tested, and shown to deliver an output power of 1.1 mW per stator at a rotation speed of 30 000 rpm. The generator has been integrated with a microfabricated axial-flow microturbine to produce a compact power conversion device for power generation and flow sensing applications.

In many engineering machines, it is necessary to pass fluid, usually air, through rotating surfaces, such as a disc or drum. This is achieved by perforating the disc with a series of holes arranged on a pitch circle. It is vital for the machine designer to know the pressure ratio required to pass a desired mass flow rate. This characteristic is defined by determination of the discharge coefficient as a function of various parameters. Until recently, the literature describing this problem was small and covered a few particular cases. More articles are appearing and this present study seeks to add to the current level of knowledge by addressing the effect of the inclinations of the holes to the tangential direction. A rig was designed and built to perform the experiments and the data were compared with the numerical analysis performed by proprietary software STAR-CD. The results indicate that the discharge coefficient is highly affected by the rotational speed and that orientating the orifices at an appropriate angle of inclination enables the discharge coefficient to be maximized. Most of the studies in the past used the ratio of tangential speed and the ideal axial velocity to represent the discharge coefficient, but it has been revealed in this paper that incidence angle is more appropriate in correlating the effect of orifice inclination and rotation on the discharge coefficient. Both the experimental and numerical results confirm that the incidence angle plays a major role in dictating the discharge coefficient of the rotating orifices.

Thermal design and management of electric machines is important for achieving higher specific power outputs and, the heat transfer in the air gaps within them require further study. Research into convective heat transfer in the gaps between the rotor and the stator has generally centered on the rotor due to interest from turbomachinery applications. This paper focuses on rotating electric machines by investigating the stator heat transfer for an idealised disk type electric machine geometry. Experiments were carried out using a thin film heating system to provide radially resolved, steady-state heat transfer data for a number of gap ratios, rotational speeds and superposed in- and out-flow rates. Results were used to provide correlations for use in analytical models and were compared with a 2D axisymmetric CFD model using the SST turbulence model. Predictions were found to agree well with local heat transfer measurements, but did not well predict the effects of ingress at the periphery.

This chapter deals with flywheels and their applications as energy storage devices in automotive powertrains. A brief introduction about flywheels is given which is followed by the historical development of flywheel usage in automobiles. The important characteristics of the flywheel are discussed including the safety aspect. This is followed by an explanation of the types of transmission needed to connect the flywheel to the vehicle's driveline. Various types of utilisation strategies of the flywheel in the vehicle are discussed using specific examples. Finally the current challenges to flywheel technology, conclusions and future trends are presented.

Flywheels are excellent secondary energy storage devices and several applications in road vehicles are under development. They can be used in hybrid vehicles with an internal combustion engine (ICE) as the prime mover or can be used in hybrid energy storage (HES) to complement the battery. When used in HES, they are utilized to load level the battery so as to protect it from peak loads and enhance its capacity and life. This paper deals with defining the main characteristics of the flywheel for an application as a secondary energy storage device for an electric vehicle. Various strategies for defining flywheels are explained. A real world customer usage data is also presented. This data is analyzed and its results are used to support the selection of the flywheel characteristics. The results show that the chosen flywheel is sufficiently sized to perform its intended tasks for a c-segment passenger car electric vehicle.

Turbocharging of internal combustion engines is an established technology used for the purpose of increasing both power density and in some cases the cycle efficiency of diesel engines relative to naturally aspirated engines. However, one significant drawback is the inability to match the characteristics of the turbocharger to the engine under full load and also to provide sufficiently good transient response. Under many conditions this results in reduced efficiency and leads to higher exhaust emissions. The design of turbocharger components must be compromised in order to minimize these drawbacks throughout the entire operating range. However, when shaft power can be either added to or subtracted from the turbocharger shaft by means of a direct drive motor-generator, an additional degree of freedom is available to the designer to achieve a better turbocharger-engine matching. Both engine efficiency and transient response can be significantly improved by means of this method, normally described as hybrid turbocharging. This paper describes the results of a theoretical study of the benefits of hybrid turbocharging over a basic turbocharged engine in both steady state and transient operation. The new system and its benefits are described and four different engine-turbocharger systems are analysed in addition to the baseline engine. The main conclusion of the paper is that a significant increase in design point cycle efficiency can be afforded by re-matching the turbocharger components under steady state conditions while at the same time improving full throttle transient performance. Emissions are not considered in this paper.

This paper describes the progress made on a small gas turbine design project undertaken by 45 final year engineering students and 15 members of staff spread across four engineering departments at Imperial College, and held over a 3-year period. The students were provided with state-of-the-art software including ProEngineer®, ANSYS®, Star CD® and the Concepts® turbomachinery design tools and the result has demonstrated that realistic designs can be produced by undergraduates with the guidance of experienced gas turbine engineers. This paper also examines the progress made, the educational goals achieved and the design and analytical lessons learnt.

The potential of the turbogenerator-based power-train for hybrid vehicles is described. Data from a small gas turbine, a prototype high-speed generator and an advanced lead-acid battery pack show that the ‘turboelectric’ concept is feasible and can provide a viable road transport solution which will comply with the stringent environmental legislation. The simulation results show improved overall vehicle efficiencies due to the implementation of regenerative braking capability. Most importantly the lean combustion of the gas-turbine engine with a suitable energy control strategy can provide lower emissions than ultra-low-emission vehicle (ULEV) limits, while an acceptable zero-emissions vehicle (ZEV) driving range can be achieved for city centres.

This paper includes small market research in the field of turboexpanders. The market research includes list of applications as well as list of some of major manufacturers of turboexpander. During the course of this research numbers of experiments were carried out to assess the performance of a small turboexpander with 65mm diameter rotor operating at relatively low speeds in comparison to standard radial turbines. The output power of the turboexpander was calculated based on the electrical output of the loading generator. The turbine rotor comprised of a TurboClaw compressor operating in reverse with two set of experiments for the following nozzles; as expander with single nozzle and a set of six nozzles. It was found that even for a non optimised geometry (rotor is a compressor not a turbine) the system efficiency for micro turboexpander is excellent.

Hybrid vehicles of different configurations and utilizing different energy storage systems have existed in development for many decades and more recently in limited production. They can be grouped as parallel, series or complex hybrids. Another classification is micro, mild and full hybrids which makes the distinction on the basis of functionality. The common energy storage systems in hybrid vehicles are batteries, supercapacitors and high speed flywheels. This paper aims to review a specific type of hybrid vehicle which involves the internal combustion engine (ICE) as the prime mover and the high speed flywheel as an energy storage device. Such hybrids are now attracting considerable interest given their potential for low cost. It is hence timely to produce a review of research and development in this subject. The flywheel is coupled to the drive line with a continuous variable transmission (CVT). The CVT can be of various types such as electrical, hydraulic or mechanical but usually in this case it is a non-electrical one. Different configurations are possible and the paper provides a timeline of the development of such powertrains with various examples. These types of hybrid vehicles have existed as prototypes for many decades and the authors believe that their development has reached levels where they can be considered serious contenders for production vehicles.