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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 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.

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.

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 systems (ESS) provide a means for improving the efficiency of electrical systems when there are imbalances between supply and demand. Additionally, they are a key element for improving the stability and quality of electrical networks. They add flexibility into the electrical system by mitigating the supply intermittency, recently made worse by an increased penetration of renewable generation. One energy storage technology now arousing great interest is the flywheel energy storage systems (FESS), since this technology can offer many advantages as an energy storage solution over the alternatives. Flywheels have attributes of a high cycle life, long operational life, high round-trip efficiency, high power density, low environmental impact, and can store megajoule (MJ) levels of energy with no upper limit when configured in banks. This paper presents a critical review of FESS in regards to its main components and applications, an approach not captured in earlier reviews. Additionally, earlier reviews do not include the most recent literature in this fast-moving field. A description of the flywheel structure and its main components is provided, and different types of electric machines, power electronics converter topologies, and bearing systems for use in flywheel storage systems are discussed. The main applications of FESS are explained and commercially available flywheel prototypes for each application are described. The paper concludes with recommendations for future research.

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 use of diesel generators to provide power for islanded grids has been the technology of choice but they generate substantial carbon emissions unless the part or all the fuel comes from a renewable source. Notwithstanding this, the engine must be sized to meet maximum demand and will operate inefficiently at part load most of the time, which is particularly bad for a synchronous constant speed engine. Given the availability of low cost solar photovoltaic (PV) systems, it is very enticing to fit a diesel generator and allow the engine to be turned off during PV generation. However, this combination will not work without some form of energy storage since it takes time for the engine to start, leading to gaps in supply and instability of the system. Lithium-ion batteries are typically considered to be the best solution to this problem because they have a high response rate, costs are lower, and they are available as products. However, they will suffer from the limited cycle and calendar life due to high cycling requirements in the application described. It is, therefore, proposed that a flywheel system could offer a lower lifetime cost alternative since only short duration bridging power storage is needed and flywheels of appropriate design can offer lower power cost than Lithium-ion battery systems. Flywheels are particularly attractive since they have a very high calendar with almost an infinite cycle life and are fully recyclable at the end of life. This research, therefore, presents an assessment of the flywheel energy storage system (FESS) as an alternative to electrochemical batteries to supplement solar PV systems backed up by diesel generators. The model of an islanded PV system combined with a diesel generator and a FESS supplying power to a residential load is implemented in MATLAB/Simulink. The results of the analysis for the cases with and without storage based on a number of different charge-discharge strategies provide evidence to support this hypothesis.

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.

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.

The development of battery electric vehicles (BEV) must continue since this offers the leading route towards a zero emission transport system. The fuel flexibility of the BEV offers the greatest potential to utilize power from renewable or low emission sources to be used in the transport system. However the limited range and high cost of the BEV remain important issues to be addressed. 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. This paper presents the modelling of a BEV which is used to study the potential for improvement in its energy efficiency. The battery model types have been discussed. The vehicle and other component models have been described. The choice of model parameters and the control strategy has been explained. The simulations have been performed on homologation and real world cycles for different scenarios. Results show significant potential for improvement in the energy efficiency of the BEV in real world usage by the utilization of a secondary energy storage device.

A theoretical analysis of magnetic couplers is recounted, leading to the design and manufacture of prototype disc type magnetic couplers. Design and development of experimental test rigs are also given. Test results are presented and compared with theoretical calculations. This shows very good agreement. The exception to the rule was the case of axial load measurements, which were not accurately evaluated by the computations. The geometries tested here showed the optimum design to consist of rotors with eight poles, magnet thickness of 10 mm and a filling factor of about 0.7.

Ceramic turbines have long promised to enable higher fuel efficiencies by accommodating higher temperatures without cooling, yet no engines with ceramic rotors are in production today. Studies cite life, reliability, and cost obstacles, often concluding that further improvements in the materials are required. In this paper, we assume instead that the problems could be circumvented by adjusting the engine design. Detailed analyses are conducted for two key life-limiting processes, water vapor erosion and slow crack growth, seeking engine design strategies for mitigating their effects. We show that highly recuperated engines generate extremely low levels of water vapor erosion, enabling lives exceeding 10,000 hs, without environmental barrier coatings. Recuperated engines are highly efficient at low pressure ratios, making low blade speeds practical. Many ceramic demonstration engines have had design point mean blade speeds near 550 m/s. A CARES/Life analysis of an example rotor designed for about half this value indicates vast improvements in slow crack growth-limited life and reliability. Halving the blade speed also reduces foreign object damage particle kinetic energy by a factor of four. In applications requiring very high fuel efficiency that can accept a recuperator, or in short-life simple cycle engines, ceramic turbines are ready for application today.

For both radial and axial turbocompressors there are well established design methods which direct the designer to the optimum shaft speed for a given flow rate and pressure rise. This shaft speed is relatively narrow in range if the highest efficiency is to be obtained. However, there are many reasons why shaft speed is dictated by other considerations and it is more common to find that the turbocompressor must operate far below the preferred shaft speed. The present contribution describes numerous applications where this occurs, the majority of which are when volume flow rates are relatively low. Many researchers have attempted to find solutions to this problem and the starting point is to take a radial compressor and design it for operation at lower than optimal speed. This creates high windage and tip leakage losses relative to the useful work component which becomes punitive as the exit blade width is reduced. In addition to this, for small machines, the size of the exit blade width itself becomes an issue as it reduces to less than around 3mm leading to high relative tip clearances and narrow passages. The purpose of this paper is to describe a novel solution that has been developed which is based on a combination of a partial entry rotor and extremely high forward sweep, a new class of machine denoted TurboClaw®. The level of forward sweep is substantial, at almost 90° that it is beyond the experience of fully bladed machines with levels of forward sweep below 30°. The machine is stable with extremely high tangential to radial Mach number ratios well over 20 being achieved. Experimentally produced maps for various sizes of machine are presented which demonstrate that the characteristic is very similar to that of an equivalent radial machine which would have to operate at speeds between two to four times greater. Further experimental work is described which has taken place on both small prototype machines and on a larger version using a specially designed test rig capable of producing accurate performance measurements based on shaft torque. The test rig has been designed to allow flow visualization and non intrusive flow measurements. A selection of results from these tests is also described. At the levels of performance reached to date this class of machine is already suitable for a number of commercial applications including fuel cell air management systems, electric supercharging, and other industrial applications. Results of research and development programs in these areas are also described.

A new class of turbomachinery has been developed to operate within the low specific speed range. This innovative forward swept turbomachine can be used in a multitude of applications currently serviced by positive displacement machines. The patented technology is described and a compressor map is presented for a size appropriate for an electrically driven supercharger for engine downsizing. The advantages of the turbocompressor in terms of simplicity of design and low tip speeds of 175 m/s lead to its reliable, robust operation and low cost manufacture. The supercharger has been evaluated using hardware in the loop simulated tests. Data shows 31% engine torque improvement over standard turbocharged engines.

Engine downsizing through inlet charging is gaining momentum for reducing engine emissions while maintaining sufficient power for customer acceptance. Small downsized engines require a smaller turbocharger, with problems of ultra high speed operation that lead to oversized, slower speed turbochargers with minimal boost and exaggerated turbo-lag problem.

A three kilowatt turboshaft engine with a ceramic recuperator and turbine has been designed for small unmanned air vehicle (UAV) propulsion and portable power generation. Compared with internal combustion (IC) engines, gas turbines offer superior reliability, engine life, noise and vibration characteristics, and compatibility with military fuels. However, the efficiency of miniature gas turbines must be improved substantially, without severely compromising weight and cost, if they are to compete effectively with small IC engines for long-endurance UAV propulsion. This paper presents a design overview and supporting analytical results for an engine that could meet this goal. The system architecture was chosen to accommodate the limitations of mature, cost-effective ceramic materials: silicon nitride for the turbine rotors and toughened mullite for the heat exchanger and turbine stators. An engine with a cycle pressure ratio below 2:1, a multistage turbine, and a highly effective recuperator is shown to have numerous advantages in this context. A key benefit is a very low water vapor-induced surface recession rate for silicon nitride, due to an extremely low partial pressure of water in the combustion products. Others include reduced sensitivity to internal flaws, creep, and foreign object damage; an output shaft speed low enough for grease-lubricated bearings; and the potential viability of a novel premixed heat-recirculating combustor.

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 2D axisymmetric and 3D 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 and the SST model was used for most of the simulations. Accepted version

Design and development of experimental apparatus is detailed for stator drag torque measurement as well as a method to evaluate rotor windage losses directly from air mass flow and temperature changes. Effects of air jets at the rotor rim were also investigated. Results are presented for air windage losses associated with ultra-high-speed machinery. These show that within the range investigated the air gap length between the rotor and the stator has an insignificant effect on windage losses. The lowest windage losses were encountered when air was forced through the rotor/stator gap from the direction of rim to bore.

A three-kilowatt turboshaft engine with a ceramic recuperator and turbine has been designed for small unmanned air vehicle (UAV) propulsion and portable power generation. Compared with internal combustion (IC) engines, gas turbines offer superior reliability, engine life, noise and vibration characteristics, and compatibility with military fuels. However, the efficiency of miniature gas turbines must be improved substantially, without severely compromising weight and cost, if they are to compete effectively with small IC engines for long-endurance UAV propulsion. This paper presents a design overview and supporting analytical results for an engine that could meet this goal. The system architecture was chosen to accommodate the limitations of mature, cost-effective ceramic materials: silicon nitride for the turbine rotors, and toughened mullite for the heat exchanger and turbine stators. An engine with a cycle pressure ratio below 2:1, a multistage turbine, and a highly effective recuperator is shown to have numerous advantages in this context. A key benefit is a very low water-vapor-induced surface recession rate for silicon nitride, due to an extremely low partial pressure of water in the combustion products. Others include reduced sensitivity to internal flaws, creep, and foreign object damage; an output shaft speed low enough for grease-lubricated bearings; and the potential viability of a novel premixed heat-recirculating combustor.Copyright © 2009 by ASME

Capturing braking energy by regeneration into an onboard energy storage unit offers the potential to reduce significantly the fuel consumption of vehicles. A common technique is to generate electricity in the motors of a hybrid electric vehicle when braking, and to use this to charge an onboard electrochemical battery. However, such batteries are costly, bulky, and generally not amenable to fast charging as this affects battery life and capacity. In order to overcome these problems, a mechanical energy storage system capable of accepting and delivering surges of power is proposed and investigated. A scale physical model of the system, based around a flywheel, a planetary gear set, and a brake, was built and operated in a laboratory. Tests showed that the proposed system could be used to store and provide braking energy between a flywheel and a vehicle, the latter emulated by an air-drag dynamometer. This validated the operating principle of the system and its computational model. Further, a computational analysis of a full-size vehicle incorporating the mechanical energy storage system was conducted. The results showed that the utilization of this system in a vehicle, when compared with a conventional vehicle, led to reductions in emissions and fuel consumption.

In recent years it has been proven that hybrid forms of powertrains in vehicles can lead to substantial reductions in fuel consumption and emissions. In particular, the advent of commercial hybrid electric vehicles proved that improved performance has been achieved by implementing a secondary energy source in a vehicle powertrain. However, the only secondary energy source implemented to date is based on electrochemical batteries, which suffer from technical and economic disadvantages. To overcome this, a novel powertrain based in both mechanical power transmission and mechanical energy storage is proposed. This article presents a brief explanation of flywheel technology as it applies to hybrid vehicles and a qualitative comparison with existing energy storage technologies is also presented. Finally computational simulations will show that the implementation of this powertrain in a vehicle leads to important reductions in fuel consumption while requiring only mechanical components in the system, instead of batteries, motors, generators and power electronics. (8 pages)

Engineering programmes within higher education have significant scope to make a contribution to global challenges such as sustainable development and solutions to world poverty. Alongside such a contribution to society, universities are also exploring ways to focus student learning around realistic enquiries. It is therefore important to explore approaches that address such challenges and pedagogies, which indeed also offer a way forward in attracting and motivating students, and in preparing them for suitable careers.We report here on an evaluation of a student-based engineering design service for development organisations, involving a partnership between a charity, a university and development professionals. The service involves teams of undergraduate students designing, making and testing intermediate technologies. The paper explores a model based around enquiry-based learning, and draws on a set of naturally-occurring reflective accounts provided by the students involved.While learning about t...

Low specific speed compressors have been historically based on positive displacement machines. Attempts to bring advantages of turbomachinery such as oil free, low parts counts, low cost of manufacture, and reliability to low flow rate applications have not been sparse, but the principle difficulty has always been that the conventional turbomachine design operates at ultra-high speed to deliver low volume flow rates. This is synonymous with low efficiency due to higher losses (windage, surface finish, and tip clearances). The innovative TurboClaw® design is a low specific speed turbomachinery with forward swept impeller geometry. It owes its high efficiency and operational stability to careful design of its nearly tangential forward swept blading and diffuser geometry. The present contribution describes the design and development of a high speed test rig to accurately measure TurboClaw efficiency using shaft torque. The test rig employs a permanent magnet high speed motor designed and developed for this purpose. The motor shaft drives a single stage TurboClaw® compressor via a high speed torque sensor. The results are presented and compared to data obtained through an energy balance method well established for this geometry since its first innovative development at Imperial College in 2003. The accurate performance measurements have been used to design and test a two stage compressor to recover energy from waste steam. This is also briefly described.

The purpose of a hybrid powertrain is to reduce fuel consumption and emissions by the regeneration of braking energy and by minimising inefficient part load operation of the engine. This must be accomplished whilst maintaining vehicle acceleration performance as expected by drivers; this currently delivered by a powerful engine, always available. Above all, the additional life cycle costs of a successful hybrid powertrain must not be significantly greater than that of the conventional engine and transmission it replaces otherwise adoption will be greatly inhibited. The majority of hybrid powertrains available commercially and under development rely on a large electrochemical battery and electric motor to provide the second means of propulsion in place of, or to supplement, the engine. The popularity of this approach is based on the availability and mature development status of batteries and electric motors. However, there are serious drawbacks in efficiency and cost, particularly when the hybrid powertrain operates most effectively in surge power mode, providing and absorbing power levels at similar levels to engine maximum output. Inefficiencies occur due to the large number of energy transformations, and battery life is limited by the number of charge and discharge cycles, an effect made worse when current levels are high. A flywheel is proposed as a superior alternative to the battery which can provide power levels as high as the engine, limited only by the capacity of the mechanical drive. High levels of energy capacity are not required as the energy stored need not exceed the kinetic energy of a vehicle travelling at moderate speed. High cost, practicality, safety and gyroscopic effects are often cited as reasons against the use of flywheels in hybrids. These are all addressed in a description of an Imperial College flywheel design that has been developed specifically for hybrid vehicle application. This flywheel has been manufactured and early test results are also reported. Even more robust, lower cost design approaches have been developed by HyKinesys and partners and these also include consideration of the CVT systems used to transmit power from flywheel to vehicle and back. The flywheel designs are better described as flycylinders, and are denoted by the name "PowerBeams" for practical commercial application. In addition to the above, the recent announcement by the FIA to allow energy storage devices to be used in Formula One in just two years time is a substantial force for change. Such systems must also be reasonably lightweight, robust and reliable. The winner in racing is then likely to challenge for supremacy on the road. Kinetic energy storage systems are amongst the potential contenders identified by the FIA.

The steady and pulsating performance results of a turbocharger mixed-flow turbine are presented. The results are taken at an equivalent speed of 70% (42,000rpm) for a pulse frequency range of 20 to 80 Hz. All instantaneous parameters required for unsteady performance evaluation are measured and discussed. Significant improvements to the measurement of instantaneous actual power have been carried out. Large variations in the operating point of the turbine occur in each pulse cycle, a velocity ratio range of 0.43 to 1.28 is seen for a 20 Hz pulse, this range reduces as the pulse frequency increases and unsteady effects become more prominent. During periods of turbine freewheeling, negative efficiencies can arise due to momentum transfer from the turbine to the working gas, although detrimental to the efficiency the energy content in these regimes are low. The use of a modified Strouhal number (MSt.) and a pressure modified Strouhal number (PMSt.) has proved useful in assessing when the onset of unsteadiness of the flow will become significant, a value of 0.1 has been used as an appropriate limit to steadiness. The results suggest that for a typical engine speed range the rotor may be considered quasi-steady whilst the turbine stage is predominately operating in an unsteady regime. Inference from the experimental data would suggest it is adequate to capture the performance of a turbine under pulsating flow using a ‘quasi-steady’ model when the MSt. < 0.1, and a ‘filling and emptying’ code when a PMSt. < 0.1 and above this value a ‘wave action’ model is more appropriate.

We have developed a MEMS power conversion device that combines an axial-flow turbine with an axial-flux electromagnetic generator. This device can generate electrical power when placed in an air-stream, and is aimed at applications such as flow sensing and power generation for remote sensors. Recent experimental performance data are presented for prototypes, and compared with CFD (computational fluid dynamics) simulations. The current devices have a volume of approximately 0.5 cm/sup 3/, generate 1 mW of output power at a pressure drop of 8 mbar and a flow rate of 35 litres per minute, and will operate at pressure drops down to a few mbar.

We have used KrF excimer laser ablation in the fabrication of a novel MEMS power conversion device based on an axial-flow turbine with an integral axial-flux electromagnetic generator. The device has a sandwich structure, comprising a pair of silicon stators either side of an SU8 polymer rotor. The curved turbine rotor blades were fabricated by projection ablation of SU8 parts performed by conventional UV lithography. A variable aperture mask, implemented by stepping a moving aperture in front of a fixed one, was used to achieve the desired spatial variation in the ablated depth. An automatic process was set up on a commercial laser workstation, with the laser firing and mask motion being controlled by computer. High quality SU8 rotor parts with diameters of 13 mm and depths of 1 mm were produced at a fluence of 0.7 J/cm2, corresponding to a material removal rate of approximately 0.3 μm per pulse. A similar approach was used to form SU8 guide vane inserts for the stators.