Publications
180 results found
Wu B, Yufit V, Marinescu M, et al., 2013, Coupled thermal–electrochemical modelling of uneven heat generation in lithium-ion battery packs, Journal of Power Sources, Vol: 243, Pages: 544-554, ISSN: 0378-7753
Abstract In battery packs with cells in parallel, the inter-cell connection resistances can cause unequal loads due to non-uniform interconnect overpotentials and consequentially lead to non-uniform heating. This article explores how load imbalances are generated in automotive applications, by describing a battery pack with finite interconnect resistances. Each cell inside the pack is represented by a pseudo 2D electrochemical model coupled with a lumped thermal model. Increasing the number of cells in parallel results in a linear increase in load non-uniformity, whilst increasing the ratio of interconnect to battery impedance results in a logarithmic increase in load non-uniformity, with cells closest to the load points experiencing the largest currents. Therefore, interconnect resistances of the order of mΩ can have a significant detrimental impact. Under steady state discharge the cell impedance changes until the loads balance. This process, however, can take hundreds of seconds and therefore may never happen under dynamic load cycles. Cycling within a narrow state-of-charge range and pulse loading are shown to be the most detrimental situations. Upon load removal, re-balancing can occur causing further heating. Simulation of a 12P7S pack under a real world load cycle shows that these effects could cause localised thermal runaway.
Offer GJ, Plant DJ, Silversides RA, 2013, A Drive Train for a Hybrid Electric Vehicle and a Method of Operating Such a Drive Train, WO2012146891 A3
A method of operating a drive train (110) for a hybrid electric vehicle, and a drive train, is disclosed. The drive train comprises an internal combustion engine (120), a first electrical machine (130) and electrical energy storage means (150). The internal combustion engine is coupled to drive the first electrical machine as a generator and the first electrical machine connected to supply electrical energy to the electrical energy storage means. The electrical energy storage means is arranged for supplying electrical energy to at least a second electrical machine (170) for driving wheels (180) of a hybrid electric vehicle. The method comprises the steps of sensing a parameter indicative of the voltage across the electrical energy storage means and, in response to this sensed parameter, controlling the internal combustion engine and/or the first electrical machine such that the first electrical machine operates to give rise to a voltage output of the first electrical machine such that the electrical energy storage means is charged without the need for power electronics.
Maher RC, Duboviks V, Offer GJ, et al., 2013, Raman Spectroscopy of Solid Oxide Fuel Cells: Technique Overview and Application to Carbon Deposition Analysis, FUEL CELLS, Vol: 13, Pages: 455-469, ISSN: 1615-6846
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- Citations: 41
Offer GJ, Plant DJ, Silversides RW, et al., 2013, Control and energy management strategies for a novel series hybrid, World Electric Vehicle Journal, Vol: 6, Pages: 288-297, ISSN: 2032-6653
In this work a novel series hybrid powertrain concept is presented. The concept removes the requirement for a power electronic converter to manage the state of charge of the accumulators by controlling the power flow between the generator and accumulator. Instead, the engine and generator are directly coupled and the state of charge of the accumulators is maintained by controlling the speed and power output of the engine to control the power flow to the accumulators. Results are presented from a proof-of-concept system that was built for a vehicle with a target peak power of 60kW with supercapacitors. Models are also presented comparing and contrasting a battery version with the supercapacitor version for a Formula Student vehicle. The powertrain is particularly suited for applications which have very high torque requirements, and hence the use of a mechanical gearbox introduces significant cost & weight, and is also ideally suited for applications where power needs to be distributed throughout an application to multiple locations, and hence multiple mechanical linkages would normally be required. The supercapacitor version is most suited to applications with high peak to average load ratios and noisy load cycles, and the battery version could be seen as a low cost route to range extend a battery electric vehicle.
Mazur C, Contestabile M, Offer GJ, et al., 2013, Understanding the automotive industry: German OEM behaviour during the last 20 years and its implications, World Electric Vehicle Journal, Vol: 6, Pages: 1054-1067, ISSN: 2032-6653
This work presents a study of how the automotive industry has responded in the last 20 years to pressures driven by economic and environmental issues, and by the transition towards electric mobility. Timelines for the major German automotive OEMs are presented to understand the industry's behaviour in the past in order to design suitable policies that are appropriate to reach future goals around the electrification of road transport. Based upon a comparison of the pressures arising in the automotive sector and the companies' behaviour with regard to technology choice and R&D, a set of hypotheses concerning this behaviour is then presented.
Maher RC, Duboviks V, Offer G, et al., 2013, In-operando Raman Characterization of Carbon Deposition on SOFC Anodes, 13th International Symposium on Solid Oxide Fuel Cells (SOFC-XIII), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1619-1626, ISSN: 1938-5862
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- Citations: 2
Duboviks V, Maher RC, Offer G, et al., 2013, <i>In</i>-<i>Operando</i> Raman Spectroscopy Study of Passivation Effects on Ni-CGO Electrodes in CO<sub>2</sub> Electrolysis Conditions, 13th International Symposium on Solid Oxide Fuel Cells (SOFC-XIII), Publisher: ELECTROCHEMICAL SOC INC, Pages: 3111-3117, ISSN: 1938-5862
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- Citations: 12
Parkes M, Refson K, d'Avezac M, et al., 2013, Determining Surface Chemistry and Vibrational Properties of SOFC Anode Materials Through <i>ab initio</i> Calculations, SOLID OXIDE FUEL CELLS 13 (SOFC-XIII), Vol: 57, Pages: 2419-2427, ISSN: 1938-5862
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- Citations: 2
Troxler Y, Wu B, Marinescu M, et al., 2013, The effect of thermal gradients on the performance of lithium ion batteries, Journal of Power Sources, Pages: accepted-accepted, ISSN: 0378-7753
Abstract An experimental apparatus is described, in which Peltier elements are used for thermal control of lithium-ion cells under isothermal and non-isothermal conditions, i.e. to induce and maintain thermal gradients. Lithium-ion battery packs for automotive applications consist of hundreds of cells, and depending on the pack architecture, individual cells may experience non-uniform thermal boundary conditions. This paper presents the first study of the impact of artificially induced thermal gradients on cell performance. The charge transfer resistance of a 4.8 Ah is verified to have a strong temperature dependence following the Arrhenius law. Thermal cycling of the cell, combined with slow rate cyclic voltammetry, allows to rapidly identify phase transitions in electrodes, due to the thermal effect of entropy changes. A cell with a temperature gradient maintained across is found to have a lower impedance than one held at the theoretical average temperature. This feature is attributed to details of the inner structure of the cell, and to the non-linear temperature dependence of the charge transfer resistance.
Lomberg M, Ruiz-Trejo E, Offer G, et al., 2013, Characterization of a Novel Ni-impregnated GDC Electrode for Solid Oxide Fuel Cell and Electrolysis Cell Applications, SOLID OXIDE FUEL CELLS 13 (SOFC-XIII), Vol: 57, Pages: 1349-1357, ISSN: 1938-5862
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- Citations: 6
Mazur C, Contestabile M, Offer G, et al., 2012, Comparing electric mobility policies to transition science: Transition management already in action?, Pages: 123-128, ISSN: 2165-4387
Driven by sustainability issues as well as economic aspects, governments have been creating and applying policies and regulations with the aim of shifting national personal transport towards electric mobility. In this context, transition science offers insights into the relevant socio-technological systems and the process of transition. This paper gives an overview of transition science, and furthermore presents current policy making by the UK and German governments that aim to manage the shift to electric mobility. A comparison of the two different policies with transition science shows that there is an overlap between the applied policy making and theory, especially for the case of the UK. Although both governments do not explicitly follow transition management their actions can be explained with the help of transition science. However, it should be noted that transition science is still a young field which needs to be further developed in order to provide policy makers with tools that enable them to manage such transitions. ©2012 IEEE.
Contestabile M, Offer GJ, North R, 2012, Electric Vehicles: A Synthesis of the Current Literature with a Focus on Economic and Environmental Viability, Publisher: LCAworks
Brightman E, Maher R, Offer GJ, et al., 2012, Designing a miniaturised heated stage for <i>in situ</i> optical measurements of solid oxide fuel cell electrode surfaces, and probing the oxidation of solid oxide fuel cell anodes using <i>in situ</i> Raman spectroscopy, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 83, ISSN: 0034-6748
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- Citations: 17
Offer GJ, Yufit V, Howey DA, et al., 2012, Module design and fault diagnosis in electric vehicle batteries, Journal of Power Sources
Systems integration issues, such as electrical and thermal design and management of full battery packs–often containing hundreds of cells–have been rarely explored in the academic literature. In this paper we discuss the design and construction of a 9 kWh battery pack for a motorsports application. The pack contained 504 lithium cells arranged into 2 sidepods, each containing 3 modules, with each module in a 12P7S configuration. This paper focuses particularly on testing the full battery pack and diagnosing subsequent problems related to cells being connected in parallel. We demonstrate how a full vehicle test can be used to identify malfunctioning strings of cells for further investigation. After individual cell testing it was concluded that a single high inter-cell contact resistance was causing currents to flow unevenly within the pack, leading to cells being unequally worked. This is supported by a Matlab/Simulink model of one battery module, including contact resistances. Over time the unequal current flowing through cells can lead to significant differences in cells’ state of charge and open circuit voltages, large currents flowing between cells even when the load is disconnected, cells discharging and aging more quickly than others, and jeopardise capacity and lifetime of the pack.
Brandon NP, Mitcheson PD, Howey D, et al., 2012, Battery Monitoring in Electric Vehicles, Hybrid Vehicles and other Applications, WO2012025706 A1
A method is disclosed of monitoring the condition of at least one cell of a battery (30), for example as used in an electric or hybrid electric vehicle (10). The battery (30) is connected to a power converter (42) to supply electrical power to an electrical load (50). The method includes the steps of: (a) controlling the power converter (42) to vary the input impedance of the power converter (42) so as to draw a varying current from the at least one cell; (b) sensing the voltage across the at least one cell and the current drawn therefrom in response to varying the impedance of the power converter (42); (c) calculating from the sensed voltage and current the complex impedance of the at least one cell; and (d) comparing the calculated complex impedance with information indicative of a correlation between (i) the complex impedance and (ii) information indicative of the condition of the at least one cell, to give an indication of the condition of the at least one cell. The varying current may be actively varied or passively varied.
Contestabile M, Offer GJ, Slade R, et al., 2011, Battery electric vehicles, hydrogen fuel cells and biofuels. Which will be the winner?, Energy and Environmental Science, Vol: 10, Pages: 3754-3772
Brightman E, Maher R, Ivey DG, et al., 2011, <i>In Situ</i> Measurement of SOFC Anode Surface Processes, 12th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1407-1419, ISSN: 1938-5862
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- Citations: 5
Offer GJ, Contestabile M, Howey DA, et al., 2011, Techno-economic and behavioural analysis of battery electric, hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system in the UK, Energy Policy, Vol: 39, Pages: 1939-1950, ISSN: 0301-4215
DECC, 2010, 2050 Pathways Analysis. Department Energy and Climate Change, 2050 Pathways Analysis, URN 10D/764
The analysis in the 2050 Pathways work presents a framework through which to consider some of the choices and trade-offs which we will have to make over the next forty years. It is system-wide, covering all parts of the economy and all greenhouse gas emissions released in the UK. It shows that it is possible for us to meet the 80% emissions reduction target in a range of ways, and allows people to explore the combinations of effort which meet the emissions target while matching energy supply and demand.
Offer GJ, Howey DA, Contestabile M, et al., 2010, Comparative analysis of battery electric, hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system, Energy Policy, Vol: 38, Pages: 24-29
This paper compares battery electric vehicles (BEV) to hydrogen fuel cell electric vehicles (FCEV) and hydrogen fuel cell plug-in hybrid vehicles (FCHEV). Qualitative comparisons of technologies and infrastructural requirements, and quantitative comparisons of the lifecycle cost of the powertrain over 100,000 mile are undertaken, accounting for capital and fuel costs. A common vehicle platform is assumed. The 2030 scenario is discussed and compared to a conventional gasoline-fuelled internal combustion engine (ICE) powertrain. A comprehensive sensitivity analysis shows that in 2030 FCEVs could achieve lifecycle cost parity with conventional gasoline vehicles. However, both the BEV and FCHEV have significantly lower lifecycle costs. In the 2030 scenario, powertrain lifecycle costs of FCEVs range from $7360 to $22,580, whereas those for BEVs range from $6460 to $11,420 and FCHEVs, from $4310 to $12,540. All vehicle platforms exhibit significant cost sensitivity to powertrain capital cost. The BEV and FCHEV are relatively insensitive to electricity costs but the FCHEV and FCV are sensitive to hydrogen cost. The BEV and FCHEV are reasonably similar in lifecycle cost and one may offer an advantage over the other depending on driving patterns. A key conclusion is that the best path for future development of FCEVs is the FCHEV.
Cordner M, Matian M, Offer GJ, et al., 2010, Designing, building, testing and racing a low-cost fuel cell range extender for a motorsport application, Journal of Power Sources
Brett DJL, Kucernak AR, Aguiar P, et al., 2010, What happens inside a fuel cell? Developing an experimental functional map of fuel cell performance, ChemPhysChem, Vol: 11, Pages: 2714-2731
Clague R, Offer G, Matian M, et al., 2009, Fuel cell racing: Imperial College London presents the Racing Green team, Pages: 302-311
Imperial Racing Green is a major initiative at Imperial College London to design, build and race zero emission vehicles in order to give students hands-on experience in the design, development and construction of fuel cell and battery vehicles, and win competitions like Formula Zero and Formula Student Class 1A, run by the Institute of Mechanical Engineers. The former competition is a time trial series for fuel cell go-carts, the latter is for single seat race cars and accommodates a wider range of technologies. The Imperial Racing Green entry to Formula Zero, codenamed IRG02, is a go-cart powered by a Hydrogenics 8kW PEM fuel cell coupled via a DC/DC converter in a current control loop to two banks of 165F Maxwell ultra-capacitors. Overall vehicle control is achieved with a National Instruments CompactRio, which also acts as a data logger. The Imperial Racing Green entry to Formula Student Class 1A, codenamed IRG03, has a modular 25kW electric drive, braking and suspension assembly at each corner. Racing Green will continue to compete in the Formula Zero Championship throughout 2009, and will compete in Formula Student Class 1A at Silverstone in July 2009. This project has demonstrated that new approaches to project based learning can generate enormous student interest and international media attention, while being rewarding to the academics and researchers involved too. This paper gives detailed information of the design of IRG02 and presents data recorded during the Formula Zero race of August 2008. A summary of the design of IRG03 is also given, concluding with lessons learnt and future plans.
Offer GJ, Brandon NP, 2009, The effect of current density and temperature on the degradation of nickel cermet electrodes by carbon monoxide in solid oxide fuel cells, CHEMICAL ENGINEERING SCIENCE, Vol: 64, Pages: 2291-2300, ISSN: 0009-2509
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- Citations: 26
Offer GJ, Mermelstein J, Brightman E, et al., 2009, Thermodynamics and Kinetics of the Interaction of Carbon and Sulfur with Solid Oxide fuel Cell Anodes, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 92, Pages: 763-780, ISSN: 0002-7820
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- Citations: 74
Adjiman C, Atkinson A, Azad A, et al., 2009, A Review of Progress in the UK Supergen Fuel Cell Programme, 11th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 35-42, ISSN: 1938-5862
Offer GJ, Shearing P, Golbert JI, et al., 2008, Using electrochemical impedance spectroscopy to compensate for errors when measuring polarisation curves during three-electrode measurements of solid oxide fuel cell electrodes, ELECTROCHIMICA ACTA, Vol: 53, Pages: 7614-7621, ISSN: 0013-4686
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- Citations: 38
Kucernak ARJ, Offer GJ, 2008, Calculating the coverage of saturated and sub-saturated layers of carbon monoxide adsorbed onto platinum, Journal of Electroanalytical Chemistry
Kucernak AR, Offer GJ, 2008, The role of adsorbed hydroxyl species in the electrocatalytic carbon monoxide oxidation reaction on platinum, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 10, Pages: 3699-3711, ISSN: 1463-9076
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- Citations: 35
Offer GJ, 2006, Low Carbon Private Vehicles, Parliamentary briefing postnote 255, Low Carbon Private Vehicles, Publisher: Parliamentary Office of Science and Technology, 255
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