Fuel Cells And Electric Vehicles Engineering Essay

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Fuel cells have been a scientific fascination since its inception in the middle of the 19th century [1]. It has come again to the scene in recent years for use in electric vehicles because of its advantages over fossil fuel with complete environmental friendliness. The dependence of the industrialized countries on oil became apparent in the oil crises [2]. More important, however, is the increasing global awareness and pressures to develop 'carbon-free' societies, where the majority of the energy will be produced from renewable technologies [3]. Controlling green house gas emissions will require a profound transformation of energy use sectors throughout the world.

Fuel cells may help to reduce our dependence on fossil fuels and diminish poisonous emissions into the atmosphere, since fuel cells have higher electrical efficiencies compared to heat engines [4].

The automotive problems technology market is likely to experiences significant change over the next 10 to 15 years, with today's incumbent internal combustion engines (ICE) coming under attach from a multitude of alternative technologies. In the short term, these will mainly be hybrid drive trains. In the longer term, fuel cells may emerge as the strongest challengers. Despite of its long history and existence of even commercialised prototypes, there are still challenges over fuel cell design in the automotive industry [5]

This project concentrates on accurate structural and dynamic design of a fuel cell car at scale. The structural developments will be judged on their influence on the performance of the vehicle. The software packages used are Solidworks and Electrochemical Impedance Spectroscopy (EIS).

Previous studies that have been made on this topic have put in evidence that a better design would give better efficiencies, so this work aims to assess such results.

1.1 Aim

The ultimate aim of the project is to assess the viability of PEM fuel cell (PEMFC) cars by designing a lab prototype. An efficient car powered by a fuel cell will be designed, built, assembled and finally tested, focusing mainly on the different behaviours of the PEMFC. This will be done by ultimately verifying how it compares with "theoretical analysis"

1.2 Objectives

The principal objectives of the project are:

Improve the car design of the predecessor project

Determine basic criteria for designing a PEM fuel cell car

Conduct different test on PEM fuel cells (and stacks), and compare the results with other data obtained from similar projects

Build a fuel cell car and test it

Analyze and draw conclusions from the results

1.3 Literature Review

As the project takes into account different aspects of fuel cells, a research for relevant works was made in all these different fields.

1.3.1 What is a fuel cell?

Electricity is the most convenient and widely-used form of energy. Electrical energy cannot be stored cheaply in large quantities, however, and in order to provide practical and flexible electrical energy sources, conversion of energy must be carried out to and from another form. [6]

In the conventional storage battery, energy stored as chemical energy within the electrode materials. The capacity of the battery is governed by the size and weight of the electrodes, which account for much of the size and weight of the battery itself. The fuel cell is a form of storage battery in which the chemical energy is stored as a fuel in a reactant tank outside the cell, and is fed to, or removed from, the electrodes when required. The electrodes are not changed in any way when the cell is operated. In this way, the capacity is governed only by the size of the "fuel" thanks, and the battery size is related only to the rate of conversion or power output.

In a narrower sense, the fuel cell may be regarded as a continuously fed battery, which converts the chemical energy of reactive "fuels" (such as hydrogen or alcohol) and oxygen (from the air) into electrical energy.

Research and development have been carried out on fuel cells over a hundred years. But it was not until the beginnings of space travel that fuel cells saw their first practical application in generating electric power (and drinking water) in the Gemini and Apollo programs [7].

1.3.2 The Advantages of fuel cells

Clearly, fuel cells have various advantages compared to conventional power sources, such as internal combustion engines or batteries. Although some of the fuel cells attributes are only valid for some applications, most advantages are more general.

What, then, are the advantages of the fuel cell that makes all this effort worthwhile?

The answer is that there is a major difference between a fuel cell and these other electricity generating plants. Fossil fuel power stations, which employ gas turbines, steam turbines or piston engines, are all reliant on the thermodynamics of heat engine. The Carnot Cycle shows us that the efficiency of any heat engine is limited to η , where,

(Eqn. 1)

W is the work done by the system (energy exiting the system as work),

QH is the heat put into the system (heat energy entering the system),

TC is the absolute temperature of the cold reservoir, and

TH is the absolute temperature of the hot reservoir.

This limits the maximum theoretical efficiency that such devices can achieve, around 40-50%, and many operate at values considerably lower than this [8]. The fuel cell, by contrast, it converts energy isothermally so is just limited by electrochemical conversion efficiency and not by Carnot Cycle. Its efficiency can reach as high as 60% in electrical energy conversion and overall 80% in co-generation of electrical and thermal energies with >90% reduction in major pollutants [9].

The fuel cell system, unlike a heat engine/generator, will have no moving parts. This leads to a high reliability operation and freedom from maintenance. The absence of moving parts makes them inherently quiet too and

Fig. 1-1. A comparison of electrical systems efficiencies between a PAFC

and other conventional energy conversions systems.

they emit relatively low levels of pollution compared to other types of generating system based on fossil fuel. Their high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints. In a fuel cell system, the fuel cell itself is nearly dwarfed by other components of the system such as the fuel reformer and power inverter. Low temperature fuel cells (PEM, DMFC) have low heat transmission, which makes them ideal for propulsion of vehicles and military applications. However, there are some disadvantages facing developers and the commercialization of fuel cells as well [10].

1.3.3 Types of fuel cell

Presently, six different fuel cell types are in varying stages of development. In general, the type of electrolyte used categorizes fuel cells. An exception to this classification is the DMFC (Direct Methanol Fuel Cell) which is a fuel cell in which methanol is directly fed to the anode. The electrolyte of this cell is not determining for the class. A second grouping can be done by looking at the operating temperature. There are, thus, low-temperature and high-temperature fuel cells. An overview of the fuel cell types is given in Table 1.

Table. 1-1. The different Fuel Cells that have been realized and are currently in use and development. [4]

1.4 Why choosing a PEM fuel cell?

Their noteworthy features include low operating temperature (up to 80°C), high power density, and easy start-up, making PEM fuel cells a promising candidate as the next generation power sources for transportation, stationary, and portable applications.

The proton exchange membrane (PEM) fuel cell is widely use for transportation applications since it is lightweight, compact and delivers high power and excellent dynamic characteristics as compared with other types of fuel cells [11]. Innovations in modern material sciences and manufacturing technologies have accelerated the development of devices of PEM fuel cells during the last decade.

PEM fuel cells have already been demonstrated in every imaginable application such as automobiles, buses, scooters, bicycles, golf carts, forklifts, airplanes, locomotives, boats, underwater vehicles, distributed power generation, cogeneration, back-up power and portable power. A logical question is 'Why fuel cells are not on the market if they are so good?' The next sections will attempt to answer this question through an analysis of the key issues and challenges in fuel cell state-of-the-art technology, applications and commercialization [12].

1.3.5 Previous studies

TO BE COMPLETED

2. PEM FUEL CELL

2.1 State-of-the-art

TO BE COMPLETED

2.2 The Principles of PEM Fuel Cell

TO BE COMPLETED

Fig. 2-1. Phenomena in a fuel cell

2.3 Operating Efficiency of a fuel cell

TO BE COMPLETED

2.4 Applications

PEM fuel cell systems are currently used in many different applications however, the end-uses can be classified in to three main groups: Transportation (including niche applications, light duty markets and buses), Stationary (large and small applications) and Portable power generation [13].

Fig. 2-2. Total number of PEM Units Installed Globally by Application [12].

2.4.1 Transportation

Almost every car manufacturer has already developed and demonstrated at least one fuel cell vehicle, and some have already gone through several iterations/generations of fuel cell vehicles. Fuel cells in transportation offer clean alternative to gasoline and diesel internal combustion engines. The main challenge for fuel cell vehicles is the size of hydrogen storage needed for an acceptable range and the cost of the fuel cells.

Fuel-cell vehicles (FCV) have been developed and demonstrated, (see Fig. 2-3 & Fig. 2-4 below). Automakers such as Toyota, Honda, Hyundai, Daimler, and General Motors (GM) have announced plans of commercializing their fuel-cell vehicles by 2015 [14].

Fig. 2-3. Fuel cell vehicles by various automakers [15]

Table 2-1. Specifications of several fuel cell vehicles [16-22]

However, among all applications for fuel cells the transportations applications involves the most stringent requirements regarding volumetric and gravimetric power density, reliability and costs.

Fuel cell buses do not have a problem with storing relatively large amounts of hydrogen (40 to 50 kg). Hydrogen is typically stored in the double roof space, which also appears to be a very safe. There are several programs, such as the European CUTE (Clean Urban Transport for Europe) and ECTOS (Ecological City TranspOrt System) and Australian STEP (Sustainable Transport Energy Project) who aim to provide bus fuel cell services in major cities around the world. Due to the CUTE and similar programs, over half of the commercialized fuel-cell buses are running in Europe, a quarter in Asia, and 15% in North America.

2.4.2 Stationary power

Large-scale central power stations have many benefits such as high efficiency, but exhibit several inherent disadvantages, e.g. the waste heat that usually cannot be efficiently utilized (due to the costly long-distance transport) and power loss during transmission. Distributed power decentralized generation is a way to resolve these disadvantages, which co-generates heat and power for household usage. - this significantly increases the overall efficiency [23]. Distributed PEM fuel cell power system is primarily focused on small scale (50-250 kW for decentralized use or <10 kW for households) [24].

However, the high cost of PEM fuel cells remains a major barrier that prohibits their widespread applications in this area. Uninterruptible power supply (UPS) for hospitals, banks and telecommunication companies receives growing interests recently because of the extremely high cost associated with power breakdowns. Several units like Plug Power GenSysTM Blue CHP [25] and Ballard FCgenTM 1030 V3 [26] fuel cell systems have been developed and deployed in many locations.

The former requires further significant improvement in fuel cell cost and lifetime. The US Department of Energy (DOE) targets for 2011 are 40,000 h of system durability at a cost of less than $750/kW, with an electrical-energy-conversion efficiency of 40% and overall efficiency of 80% [27]. However, currently few fuel cell units have exhibited a lifetime over 10,000 h.

2.4.3. Portable applications

Another promising area is portable power supply, considering that limited energy capacity of batteries unlikely meets the fast-growing energy demand of the modern portable electric devices such as laptops, cell phones and military radio/communication devices. PEM fuel cells provide continuous power as long as hydrogen fuel is available and they can be fabricated in small sizes without efficiency loss. Major electronics companies, such as Toshiba, Sony, Motorola, LG, and Samsung, have in-house R&D units for portable fuel cells.

The fast-growing power demand by portable electronic devices is unlikely satisfied by current battery technology because of its low energy power capability and long charging time. These two issues can be well resolved by using portable/micro PEM fuel cells. Consequently, global production of portable fuel cells has continuously grown. Over two-thirds of these units are based on regular PEM fuel cells, a quarter of them consist of DMFC (direct methanol fuel cell) units and the remaining 6% are not related to PEM technology [28]. The typical power range for portable electronic devices is 5-50W and several developments focus on a level of <5W for micro power application [29]. A wider range of power, 100-500 W, has also been considered [30].

2.5 Challenges in fuel cell development

Great deal of efforts has been made in the past, particularly during the last couple of decades or so, to advance the PEM fuel cell technology and fundamental research. Factors such as durability and cost still remain as the major barriers to fuel cell commercialization. Issues such as water and heat management, and new material development remain the focus of fuel-cell performance improvement and cost reduction.

A fuel cell stack needs a supporting system in order to be operational. The supporting subsystems include fuel supply, oxidant supply, heat management, water management, power management and conditioning and instrumentation and controls. System design and its complexity also very much depend on application. The following are the challenges on the fuel cell system.

2.5.1 System efficiency

The system efficiency is lower than the stack efficiency due to power requirements for auxiliary components and due to power conversion. A well-designed system should not use more than 10% of the fuel cell output power for auxiliary components. The efficiency of DC/DC or DC/AC converters is relatively high (typically >90%) but their number and configurations must be optimized for the given application. Systems with a reformer should reach 40% efficiency and hydrogen-fueled systems should have efficiency around 50%.

2.5.2 Operation at higher temperatures

The need for operation at high temperatures has already been mentioned. A higher operating temperature would reduce the size of the heat rejection equipment. In addition, operation at >100°C would greatly simplify water management inside the fuel cell because all water inside the fuel cell would be in the vapor phase. The challenge is to develop a polymer membrane that can operate at high temperature and still satisfy the performance and durability criteria [50, 51].

2.5.3 Water balance

Water is produced in the electrochemical reaction inside the fuel cell. At the same time water is needed for the humidification of reactant gases. The system design must ensure that there is no need for supplying additional water to the system, which may be impractical for transportation applications.

2.5.4 Freezing

For many potential applications a fuel cell system must be capable of surviving and operating in extreme conditions. The presence of water in the membrane and fuel cell requires special attention to fuel cell stack and system design to allow system survival and start-up in extremely cold conditions. Most automotive systems have already demonstrated this capability [52, 53].

2.5.5 Fuel issues

In order to bring the fuel cell systems to the market sooner than hydrogen may become a widely available fuel, fuel cell systems may be equipped with a reformer that generates hydrogen-rich gas from hydrocarbon fuels. This poses several challenges to the fuel cell stack and system design. Carbon monoxide, even in small quantities, is a poison for Pt catalyst at normal operating temperatures. Controlling a fuel cell/reformer system in variable power mode and maintaining low CO level all the time is a very challenging task. In addition, several other contaminants may be generated in the reforming process, which may have a detrimental efficiency performance and durability.

2.5.6 Infrastructure

If anything approaching a 'hydrogen economy' is ever to be realised, it will be necessary to be able to produce and supply hydrogen to the public in the same general way as gasoline and diesel oil do nowadays. This requires the development of safe methods of generating hydrogen either centrally, at the refuelling station, or even in the home.

3. FUEL CELL EXPERIMENT

TO BE COMPLETED

4. CAR DESIGN

In previous studies, the design of a lab car was really poor. It has been addressed that a more powerful fuel cell was needed and the weight of the car needed to be reduced.

For the design of normal road-going vehicles, the most important aerodynamic factor is the drag force. The total force resisting the forward motion of a road vehicle comes partly from the rolling resistance of the wheels, and partly from aerodynamic drag. There are considerable economic and performance advantages to be gained from drag reduction.

Fig. 4-1. Image of HySpeedster [41]

If we want to design a more efficient car, we need to take these factors into consideration. Although the drag is a factor to consider at high speeds. The materials used in vehicles nowadays are selected so as to optimally fulfil the specific requirements. Since materials play a decisive role with regard to both the quality and cost of a car, selection of the correct materials at the earliest possible stage of the development process is of vital importance. Even though, our car, it would be just a scale car and it has just been made for scientific purposes.

4.1 Chassis design

The chassis model was created in Solidworks using Audi R8 as a blueprint [34]. The initial sketch of the car can be seen in figure 4-2. The car was designed from a series of foam sheets held together with steel screws. The chassis itself is very light yet stiff, however when adding the motor, battery and driver the car becomes much more massive. By the time of construction, the EDMC suggested that the best material available was a type of foam composite, really light, which would give the car stiffness and lightness.

Fig. 4-2. Initial Chassis Sketch.

Each component of the chassis was modeled in Solidworks. The components were measured using a variety of high precision engineering tools and a general accuracy of ±1 mm was achieved. All of the components of the car were modelled in Solidworks to produce a highly detailed and accurate initial model. This model was used to measure the total mass of the chassis without the car. Some parts of the car were not included due to the vast complexity of modelling certain components. These included the brake levers, callipers and transmission lines; the electrical wiring and circuitry and the seat and seatbelts. Some of the models were greatly simplified; the wheels, batteries, motor, drive belt, drive gear and battery;. In general the model is high detail yet the masses and inertial matrices must be assumed to be simplified and not precise.

Fig. 4-3. Final design of the chassis

4.2 Gas storage tanks design

TO BE COMPLETED

4.3 Car plate design

TO BE COMPLETED

4.4 Gearbox design

TO BE COMPLETED

4.5 Control system design (electronics)

TO BE COMPLETED

5. CAR TESTING

TO BE COMPLETED

6. CONCLUSION

TO BE COMPLETED

7. FURTHER WORK

TO BE COMPLETED

8. BIBLIOGRAPHY

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[2] D.Hart, Journal of Power Sources 2000, 86, 23.

[3] P.J. Hamilton and B.G. Pollet, Polymer Electrolyte Membrane Fuel Cell (PEMFC) Flow Field Plate: Design, Materials and Characterisation; FUEL CELLS 10, 2010, No.4, 489-509.

[4] L. Carrette, K.S. Friedrich and U. Stimming, Fuel Cells - Fundamentals and Applications; FUEL CELLS 01, 2001, No.1, 5-39.

[5] H.G Dusterwald, J. Gunnewing and P. Radtke, DRIVE - The Future of Automotive Power: Fuel Cells Perspective; FUEL CELLS 07, 2007, No.3, 183-189.

[6] Intergovernmental Panel on Climate Change, Climate Change 2007 Fourth Assessment Report, http://www.ipcc.ch/ipccreports/assessments-reports.htm, 2008.

[7] Gregor Hoogers, 2003. Fuel Cell Technology Handbook, CRC Press.

[8] Tao, R.; Huang, K.; Tang, H.; Bell, D. Response to the comments: Fuel efficiency of internal combustion engines. Energy and Fuels, v 23, n 6, p 3339-3342, June 18, 2009

[9] Papageorgopoulos D. DOE fuel cell technology program overview and introduction to the 2010 fuel cell pre-solicitation workshop. DOE fuel cell pre-solicitation workshop. Department of Energy, Lakewood, Colorado; 2010.

[10] Gemma Crawley. 2006 PEM Survey. Fuel Cell Today 2006

[11] Hwang JJ, Wang DY, Shih NC. Development of a lightweight fuel cell vehicle. Journal of Power Sources 2005;141:108-15.

[12] F. Barbir and S. Yazici. Status and development of PEM fuel cell technology. INTERNATIONAL JOURNAL OF ENERGY RESEARCH 2008; 32:369 - 378

[13] Lisa Callaghan Jerran. Light Duty Vehicle Survey 2009, Fuel Cell Today 2009

[14] Gittleman C, DM, Jorgensen S, Waldecker J, Hirano S, Mehall M. Automotive fuel cell R&D needs. In: DOE fuel cell pre-solicitation workshop. Department of Energy, Lakewood, Colorado; 2010.

[15] Google. Google image search: fuel cell vehicles. 2010 http://www.google.co.uk/images?client=safari&rls=en&q=fuel%20cell%20vehicles&oe=UTF-8&redir_esc=&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi [23.11.10]

[16] Honda. Honda FCX clarity official web site; 2007.

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[19] Toyota, Toyota 2007 North American Environmental Report, Toyota, 2007.

Energy and Climate Section, p. 9.

[20] Toyota. Toyota FCHV acquires vehicle type certification; 2005. <http://

www.worldcarfans.com/10506178923/toyota-fchv-acquires-vehicle-type-certification> [24.11.10]

[21] McCausland, E. Autoshows: 2009 Kia Borrego FCEV Fuel Cell Vehicle; 2008.

<http://www.automobilemag.com/auto_shows/2008_los_angeles/0811_kia_borrego_fcev_fuel_cell_vehicle/index.html>. [24.11.10]

[22] Daimler. Mercedes-Benz B-Class F-CELL: First electric car fully suited for everyday driving and with the driving dynamics of a two-litre petrol car; 2009. <http://media.daimler.com/dcmedia/0-921-1258086-1-1258427-1-0-0-0-0-1-11702-854934-0-1-0-0-0-0-0.html?TS=1270254293953>. [25.11.10]

[23] Geiger S, Copper MAJ. Fuel cell small stationary market survey. Fuel Cell Today 2003.

[24] Garche J, Jorissen L. PEMFC fuel cell. In: Vielstich W, Gasteiger H, Lamm A, editors. Handbook of fuel cells: fundamentals, technology and applications. John Wiley & Sons, Ltd.; 2003.

[25] Plug Power GenSysTM Blue CHP http://www.plugpower.com/products/residentialgensys/gynsysdocumentation_literature/gensysvideo.aspx

[26] Ballard FCgenTM 1030 V3 http://www.ballard.com/files/pdf/Case_Studies/BUP_Emergency_Economic_Benefits_040110.pdf

[27] EERE UD. Hydrogen, fuel cells & infrastructure technologies program multiyear research, development and demonstration plan. In: EERE D, editor. 2007.p. 24.

[28] Butler J. Portable fuel cell survey 2009. Fuel Cell Today 2009.

[29] Lipman T, Sperling D. Market concepts, competing technologies and cost challenges for automotive and stationary applications. In: Vielstich W, Gasteiger H, Lamm A, editors. Handbook of fuel cells: fundamentals, technology and applications. John Wiley & Sons, Ltd.; 2003. p. 1318-28.

[30] Narayanan SR, Valdez TI, Rohatgi N. Portable direct methanol fuel cell system. In: Vielstich W, Gasteiger HA, Lamm A, editor. Handbook of fuel cells. John Wiley and Sons; 2003.

[33] Pekhota F, Rusanov V, Fateev V. Progress in fuel-cell development and possible market in Russia. In: Proceedings of the 13th World Hydrogen Energy Conference, Beijing, China, 2000. p. 156-60.

[34] http://www.the-blueprints.com/blueprints/cars/audi/22125/view/

[35] UK Climate Change Act of 2008,

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[53] Fuel Cells Bulletin. Honda FCX demonstrates cold-start performance. Fuel Cells Bulletin 2004; 2004(4):5.

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