A comparison of evaporative and liquid cooling methods for fuel cell vehicles

Despite having efficiencies higher than internal combustion engines, heat rejection from fuel cells remains challenging due to lower operating temperatures and reduced exhaust heat flow. This work details a full system simulation which is then used to compare a conventional liquid cooled fuel cell system to two types of evaporatively cooled fuel cell systems. Both steady state and transient operation are considered. Results show the radiator frontal area required to achieve thermal and water balance for an evaporatively cooled system with an aluminium condensing radiator is 27% less than a conventional liquid cooled system at 1.25 A/cm2 steady state operation. The primary reason for the reduction is higher heat transfer coefficients in the condensing radiator due to phase change. It is also shown that the liquid water separation efficiency has a significant influence on the required radiator frontal area of the evaporatively cooled system

A comparison of evaporative and liquid cooling methods for fuel cell vehicles

Despite having efficiencies higher than internal combustion engines, heat rejection from fuel cells remains challenging due to lower operating temperatures and reduced exhaust heat flow. This work details a full system simulation which is then used to compare a conventional liquid cooled fuel cell system to two types of evaporatively cooled fuel cell systems. Both steady state and transient operation are considered. Results show the radiator frontal area required to achieve thermal and water balance for an evaporatively cooled system with an aluminium condensing radiator is 27% less than a conventional liquid cooled system at 1.25 A/cm2 steady state operation. The primary reason for the reduction is higher heat transfer coefficients in the condensing radiator due to phase change. It is also shown that the liquid water separation efficiency has a significant influence on the required radiator frontal area of the evaporatively cooled system

An electric vehicle model and validation using a Nissan Leaf: a Python-based object-oriented programming approach

Electric vehicles are becoming more and more prevalent, especially with major manufacturers announcing that they will be focusing on electric or hybrid vehicles in the future. This article describes an object-oriented approach to a vehicle model using Python 3. This approach allows for flexibility of vehicle design. The key parameters were input to define the specific vehicle for validation, in this case a Nissan Leaf. It is anticipated that this flexibility will lead to rapid exploratory design of vehicle variants, such as four-wheel drive, independent wheel drive and multiple electrical sources. The model had its objects individually validated before the whole vehicle was verified against common drive cycles and a real-world drive in the United Kingdom recorded using an On-board Diagnostics (OBD2) Bluetooth dongle

Energy economy analysis of the G-Wiz: a two-year case study based on two vehicles

This paper presents the data recorded from two G-Wiz Reva electric vehicles (EVs) over a period of two years and approximately 8000km on each vehicle. The analysis of the vehicle data demonstrates that the range of the vehicle obtained for a certain state-of-charge (SOC) drop was not consistent. The results show that the main factor affecting the available range was irregular vehicle usage. The recharge energy consumption patterns of the vehicle were identified and it was demonstrated that infrequent vehicle usage increased energy consumed by the vehicle. A maximum range of 66.8km was achieved when the vehicle was regularly used, but this fell to 42.8km when it was infrequently used. The energy economy when the vehicle was regularly used was 8.3 km/kWh. Additionally, the analysis results identify the need to determine discharge rate of the vehicle batteries to determine the precise effects on the available range and energy consumption of the vehicle

Comparison of Fuel Consumption and Fuel Cell Degradation Using an Optimised Controller

The Energy Management Strategy (EMS) of any hybrid vehicle is responsible for determining the operating state of many components on board the vehicle and therefore has significant effect on the fuel economy, emissions, ageing of components and vehicle drive-ability. It is generally accepted that Stochastic Dynamic Programming (SDP) can be used to produce a near-optimal control strategy provided that an accurate Markov model of the drive-cycle is available, and the cost function used for the optimisation is representative of the true running cost of the vehicle. The vast majority of research in this field focussing solely on the optimisation of the fuel economy, however for a fuel cell hybrid vehicle, the degradation of the fuel cell contributes significantly to the overall running cost of the vehicle, and should therefore be included in calculation of the running cost during the optimisation process. In this work, an optimised controller using SDP is developed for a campus passenger vehicle in order to minimise the lifetime cost of both fuel consumption and fuel cell degradation. The vehicle is then simulated over a number of typical journeys obtained from data logging during its use on the University of Birmingham's campus. It is shown that the expected lifetime cost due to fuel cell degradation massively outweighs the cost of the fuel consumed

An evaluation of business simulation games for the Management module of the MEng Aeronautical Engineering degree at Loughborough University

There is a drive within engineering disciplines at Loughborough University to develop the employability skills of undergraduate students. The engCETL (Engineering Centre for Excellence in Teaching & Learning) has a broad remit to enhance links with industry and to underpin developments in learning and teaching with pedagogic research and technology development. The Centre does this through research and development projects that are proposed by academics within the engineering related departments and carried out in conjunction with specialists from the engCETL team. Prof Rob Thring, Head of the Aeronautical and Automotive Engineering Department proposed a project to the engCETL. His requirement was for some form of business simulation software for the undergraduates to use as part of the Management module on the MEng programme. Currently the students come up with an idea for a new business, create a business plan for the venture and take part in a ‘Dragons’ Den’ style presentation at the end of the project to representatives from the department and industry. However, the department would like to take this project a step further and provide the students with the opportunity to take part in a simulated business environment where they could explore the idea of setting up or running a business as close to the real world as possible. The intention would be to enliven and enrich the student’s learning experience with skills development such as; enterprise, leadership, management, teamwork, fiscal sense, business judgement and inventiveness amongst others. An interdisciplinary project team was formed to try and resolve the pedagogic, technical and business aspects that would need to be addressed in order to implement such software within the MEng programme. The approach taken has been to form a set of criteria based on certain curriculum requirements but keep the brief broad and carry out a scoping study of existing software (commercial and open source) and take account of the academic literature in this area. After the initial scoping study, our findings indicate two commercial business simulations that have potential for use on the course. These were; ‘Marketplace Simulation’ (http://www.marketplace-simulation.co.uk) and SimVenture (http://www.simventure.co.uk). An in-depth evaluation was then carried out for the two simulations. This evaluation comprised two teams made up of academics, industrial representatives and engCETL staff. The software was thoroughly examined in terms of what each application could offer to the learning experience of the students, resources to support staff and the costs involved, for example, staff time in embedding the software into the curriculum.This paper will highlight the approach taken, findings and recommendations from the evaluation of the two business simulations. The recommendations will be presented in the context of all engineering disciplines and will cover; appropriateness of the chosen software for the programme level, plans for embedding into the curriculum, potential learning outcomes and assessment methods. It will benefit all those interested in methods for evaluating potential simulation games for suitability within the curriculum and the development of enterprise and employability skills

Polymer electrolyte fuel cell transport mechanisms: a universal modelling framework from fundamental theory

A mathematical multi-species modelling framework for polymer electrolyte fuel cells (PEFCs) is presented on the basis of fundamental molecular theory. Characteristically, the resulting general transport equation describes transport in concentrated solutions and also explicitly accommodates for multi-species electro-osmotic drag. The multi-species nature of the general transport equation allows for cross-interactions to be considered, rather than relying upon the superimposition of Fick’s law to account for the transport of any secondary species in the membrane region such as hydrogen. The presented general transport equation is also used to derive the key transport equations used by the historically prominent PEFC models. Thus, this work bridges the gap that exists between the different modelling philosophies for membrane transport in the literature. The general transport equation is then used in the electrode and membrane regions of the PEFC with available membrane properties from the literature to compare simulated one-dimensional water content curves, which are compared with published data under isobaric and isothermal operating conditions. Previous work is used to determine the composition of the humidified air and fuel supply streams in the gas channels. Finally, the general transport equation is used to simulate the crossover of hydrogen across the membrane for different membrane thicknesses and current densities. The results show that at 353 K, 1 atm, and 1 A/cm2, the nominal membrane thickness for less than 5 mA/cm2 equivalent crossover current density is 30 mm. At 3 atm and 353 K, the nominal membrane thickness for the same equivalent crossover current density is about 150 mm and increases further to 175 mm at 383 K with the same pressure. Thin membranes exhibit consistently higher crossover at all practical current densities compared with thicker membranes. At least a 50 per cent decrease in crossover is achieved at all practical current densities, when the membrane thickness is doubled from 50 to 100 mm

An energy management strategy to concurrently optimise fuel consumption & PEM fuel cell lifetime in a hybrid vehicle

The cost and reliability of fuel cells are major obstructions preventing fuel cell hybrid electric vehicle (FCHEV) from entering the mainstream market. However, many of the degradation methods are strongly affected by the operating conditions of the fuel cell and therefore can be mitigated by optimisation of the Energy Management Strategy (EMS). The major causes of fuel cell degradation are identified from the literature and a model is produced in order to estimate the effect of the EMS on the fuel cell degradation. This is used to produce an optimal strategy for a low speed campus vehicle using Stochastic Dynamic Programming (SDP). The SDP controller attempts to minimise the total running cost of the fuel cell, inclusive of both fuel consumption and degradation, each weighted by their respective costs. The new strategy is shown to increase the lifetime of the fuel cell by 14%, with only a 3.5% increase in fuel consumption, largely by avoiding transient loading on the fuel cell stack

Polyethylene-carbon material for polymer electrolyte membrane fuel cell bipolar plates

Bipolar plates are the interconnects between cells within a fuel cell stack. They must be highly electrically conductive in order to maximize the voltage across the stack and must be highly thermally conductive to aid cooling of the stack. Traditionally, bipolar plates are made from graphite or stainless steel; both have drawbacks such as low mechanical strength and corrosion problems, respectively. In order to overcome the problems associated with these common materials and to improve on the electrical and thermal conductivity aspects as well as decrease costs and improve manufacturability, a mixture of polyethylene and carbon was investigated. Composites of polyethylene and carbon were mixed using a two-roll mill and injection moulded. Micrographs of the polyethylene-carbon (PE-C) blends show how the microstructure of the polyethylene network and carbon particles provide increased mechanical properties but further addition of carbon leads to the degradation of these properties. Increasing carbon content led to an ever-increasing electrical conductivity. The material was tested for tensile and flexural properties, resulting in a maximum tensile and flexural strength of ∼24 MPa (at 26 wt% carbon in polyethylene) and ∼35 MPa (at 40 wt% carbon in polyethylene), respectively. The samples displayed electrical conductivity, with a maximum of 1.19 S/cm in-plane and 1.05 S/cm through-plane being achieved at a carbon loading of 65 wt%. The PE-C composite displayed low densities of 1.56 g/cm3 and desirable mechanical strength close to the US Department of Energy target level of 44.26 MPa for flexural strength. It was concluded that PE-C composites with different types of carbon and carbon fibres should be tested in order to reach the electrical conductivity target levels of 100 S/cm

A polymer electrolyte membrane fuel cell model with multi-species input

With the emerging realization that low temperature, low pressure polymer electrolyte membrane fuel cell (PEMFC) technologies can realistically serve for power-generation of any scale, the value of comprehensive simulation models becomes equally evident. Many models have been successfully developed over the last two decades. One of the fundamental limitations among these models is that up to only three constituent species have been considered in the dry pre-humidified anode and cathode inlet gases, namely oxygen and nitrogen for the cathode and hydrogen, carbon dioxide, and carbon monoxide for the anode. In order to extend the potential of theoretical study and to bring the simulation closer towards reality, in this research, a 1D steady-state, low temperature, isothermal, isobaric PEMFC model has been developed. The model accommodates multi-component diffusion in the porous electrodes and therefore offers the potential to further investigate the effects of contaminants such as carbon monoxide on cell performance. The simulated model polarizations agree well with published experimental data. It opens a wider scope to address the remaining limitations in the future with further developments