Top Banner
Fuel Cell Science & Technology – ME 6580 Khalil Raza – Wright State University 1 Fuel Cell Sciences and Technology – ME 6580 Fuel Cell Electric Vehicles Graduate Project – Report Khalil Raza
15
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

1  

           

Fuel  Cell  Sciences  and  Technology  –  ME  6580          

Fuel  Cell  Electric  Vehicles    

Graduate  Project  –  Report    

Khalil  Raza                                                        

Page 2: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

2  

Contents      Introduction    Operation  of  Fuel  Cells    Chemistry  of  Fuel  Cells    Types  of  Fuel  Cells:  

Polymer Electrolyte Membrane Fuel Cells (PEMFC)

Direct Methanol Fuel Cells (DMFC)

Phosphoric Acid Fuel Cells (PAFC)

Molten Carbonate Fuel Cells (MCFC)

Basic Components of Fuel Cell Vehicles:

The Motor

Transmission of Fuel Cell Vehicles

AC Motor Controller

Regenerative Braking

Ultracapacitors

Hydrogen Production

Hydrogen Storage for Fuel Cell Vehicles

Metal Bounded Hydrogen Storage

Storing Hydrogen as Liquid

Hydrogen Storage in Carbon Nanotubes

Conclusion

References

Page 3: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

3  

1. Introduction:

Fuel Cell is one of the emerging technologies with an immense potential to fill the energy

gap created by oil shortages. It is the direct energy conversion process in which the

chemical energy of fuel primarily hydrogen is converted to electrical energy. Fuel Cell

takes oxygen from air and uses hydrogen as a fuel to generate electricity using an

electrolysis process. In addition to this, it generates water and heat as by-products.

According to energy experts, there is a great future for fuel cells and we may see fuel

cells generating electrical power. It is much cleaner and environmental friendly power

generation than many other conventional power processes. Fuel Cells are majorly used

for three types of application that includes the transportation, stationary and portable

power.

Fuel Cells for large stationary power are bigger in size and have high working

temperatures. They can produce power equivalent to current conventional power plants

and can be used as load center for high electricity demands. The fuel cells for portable

devices are reasonably extremely small that are used to power up small devices like cell

phones, laptops, computers etc. Fuel cells for transportation can be small to medium

sizes. They are installed under the hood of the vehicles along with other auxiliary devices

that make up the whole fuel cell system. In my this research paper I will be focusing on

the fuel cells that are used for the transportation system. Almost, in most cases the fuel

cells used for the transportation are the Polymer Electrolyte Membrane or Proton

Exchange Membrane fuel cells (PEMFC).

 Hydrogen is the commonly used fuel in the fuel cells. Besides, the hydrocarbons such as

natural gas and methanol are also used as fuel. Fuel Cells seems similar to batteries as

they both work on electrochemical process but the major difference is that in Fuel Cells

the energy is produced while in the batteries the energy is stored in the chemical form.

Fuel cells continue to produce electricity as long as the fuel is fed into the device.

The idea of using Fuel Cell to produce electricity was put forwarded by a German

Physicist Christian Fridrech Schönbein in 18381. Later NASA space programs made use

Page 4: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

4  

of fuel cells commercially to produce power for space vehicles. Afterwards, the fuel cells

have been put in use to produce power for almost all kind of electricity consuming

applications that includes residential, industrial and commercial. Due to the shortage of

oil and its increasing prices, almost all the automotive companies are investing in fuel

cell technology. Automotive sector takes a huge amount of oil resources that is expanding

exponentially every year. Therefore, companies are looking for more sustainable process

of transportation that could cater the future needs while also keeping the environmental

problems in view as an important factor.

Thus the fuel cell can be the most promising technology that could solve the

transportation problems of the globe while also contributing positively to the

environment. Since the fuel cell goes through the electrolysis process and it takes oxygen

from air and hydrogen as fuel so it emits only water from exhaust tailpipe. Moreover, the

conventional car use internal combustion engines, their efficiency are 20 percent to

produce power and rest of the 80 percent of energy is lost and dumped into our

environment as heat or thermal energy. Since, the engine uses heat from combustion of

fuel to build up pressure and transforms that pressure to mechanical work through piston

and crankshaft mechanism. The 80 percent of the heat is lost due to less efficient thermal

efficiency. During this process heat is dumped into an atmosphere, which poses a great

threat to our environment. This act as catalyst to radically change the standard parameters

of nature resulting in climate change and global warming. As human beings on this planet

it is highly preemptive to protect the surroundings and live sustainably while moving

forward to future. Whereas, the fuel cells use electric motors that are fairly efficient up to

80 – 90 percent. In recent years there has been major breakthrough in this technology

however, the future of this fuel cell technology still depends on many factors. Amongst

those factors the production of hydrogen at economical level is the prominent one.

Along-with that the infrastructure development, on-board fuel tank and on board fuel cell

will determine the real future of this technology.

There are different types of fuel cells being used in industry for commercial and

residential purposes depending upon the type of the application. The most important

Page 5: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

5  

factor determining which of the fuel cell systems to be used for particular application

depends on the temperature range. Fuel cells have the temperature range starting from 90

Celsius to 700 Celsius. Polymer Electrolyte membrane fuel cells (PEMFC) have the

temperature range from 80 – 90 Celsius this makes it applicable to use it in fuel cell

vehicles. It is easier to manage the heat in PEM Fuel cells. The fuel cells have typical

configuration that have one electrolyte, two electrodes – cathode and anode. Commonly,

fuel cells are also classified according to the electrolytes as well.

With close analysis of the above figure, it can easily be predicted that the future of fuel

cell is really bright. Since the year 2000, there has been a great progress made in this field

and it is believed that this will continue to grow in future and the growth rate will be

exponential. Therefore, it is high time for everyone involved in technological

development sector to support this green technology and make our future more

sustainable.

Figure  1:  This  chart  shows  the  development  in  fuel  particularly  in  the  areas  of  Hydrogen  production  and  its  storage  before  2000  till  2012.  Source:  https://www1.eere.energy.gov/hydrogenandfuelcells/images/fct_graph_accelerating_commercialization.gif  

 

Page 6: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

6  

2. Operation  of  Fuel  Cells: A fuel cell system works on the basis of electrochemical process that needs fuel, oxidant

or air and coolant to maintain the working temperature of the fuel cell systems. Besides,

it requires the proper pressure, flow rate of oxygen and fuel to regulate the systems

according to standard operating conditions of the fuel cells systems. Therefore, along-

with the fuel cell stacks, the fuel delivery system, air system and humidification system is

also installed to get the optimum level of energy from the fuel cells. As the fuel cells

generate the power the must be inverted to required form of source which would be used

to power a particular device. For example, the fuel cells generate power in direct current

and that has to be converted to AC power through a DC to AC inversion system.

 

Figure  2:  Chemistry  of  Proton  Exchange  Membrane  Fuel  Cell    Source:  http://www.hydrogen-­‐fuelcells.com/2012/08/hydrogen-­‐fuel-­‐cell-­‐and-­‐its-­‐amazing.html

Page 7: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

7  

3. Chemistry of Fuel Cell Systems: As already stated in the introduction section that a fuel cell consists of an electrolyte and

cathode and anodes as two of its electrodes. The anode supplies electrons and cathode

receives the electrons. The cathode and anode are separated by an electrolyte. The

electrolyte conducts ions between cathode and anode in order to complete the cycle of the

circuit. When hydrogen is supplied as a fuel to the anode, it is oxidized generating the

hydrogen ions and electrons. Whereas, at the cathode the oxygen is fed where the

hydrogen ions from the anode absorb the electrons and produce water by reacting with

oxygen2.

 

4. Types of Fuel Cells: Fuel cells are classified according to their Electrolytes. Different electrolytes have

different working conditions thus are used for different application. Following are the

basic commonly fuel cells for the power generation:

1. Polymer Electrolyte Membrane Fuel Cells (PEMFC):

In PEMFCs the working temperature is considerably lower than other types of fuel cells

less than 90 degrees Celsius3. Therefore, more applicable for the vehicular application. A

membrane is used to separate the electrodes, which is used as catalyst for the proton

conduction. Primarily this type of fuel cells is used for portable application, back up

power and automotive vehicles.

2. Direct Methanol Fuel Cells (DMFC):

Direct methanol fuel cell comes under the category of the proton exchange membrane

fuel cells. They use methanol as the fuel. The major benefit of using this kind of fuel cell

is the methanol as a fuel, which is very easy to transport and its energy density is very

high. Methanol is non-volatile in liquid state. The downside of DMFC is that their

efficiency is quite low4. When the circumstances demands for higher power density over

higher efficiency DMFCs are well preferred.

3. Phosphoric Acid Fuel Cells (PAFC):

Phosphoric Acid Fuel Cell as the name suggests, they use liquid phosphoric acid as the

electrolyte. The anode and cathode are carbon paper coated with platinum catalyst5.

Page 8: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

8  

Positive charge ions flow through electrolyte from anode to cathode. Finally the electrons

produced are passed through an external circuit powering up the device with direct

electric current.

4. Molten Carbonate Fuel Cells (MCFC):

Molten Carbonate Fuel Cells use mixture of hydrogen and carbon monoxide produced

from water and fuel. Molten potassium lithium carbonate is used as electrolyte, which

carries out the process of producing electricity at the temperature of about 650 degree

Celsius6.

 

Figure  3:  This  shows  the  different  fuel  cell's  fuel,  electrolyte,  and  temperature  range.  Source:  http://www.fuelcells.org/fuel-­‐cells-­‐and-­‐hydrogen/types/    

Page 9: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

9  

5. Basic Components of Fuel Cell Vehicles 1. The Motor:

Fuel Cell vehicles use an electric motor instead of internal combustion engines to get

mechanical power. Electric motors have many advantages over conventional internal

combustion engines in terms of high torque and they can achieve wide revolutions per

minute (RPM). Fuel cell vehicles can be powered through both the AC motors and DC

motors. A DC motor is quite simple in its operation and less expensive than Alternating

Current (AC) motors. It is very easy to control and regulate the DC motors.

Notwithstanding, DC motors are hard to find in bigger sizes to power up the vehicles and

they require more maintenance as well. The heavier downside of DC motors is that these

are not efficient when used as generators. Since, the basic goal is to achieve maximum

efficiency in fuel cell vehicles. The DC motors cannot generate power through

regenerative braking. Thus reducing down the overall efficiency of the system of the

vehicle. Whereas, the AC motor can perform this task very well. That is the reason the

AC motors are generally preferred over DC motors to be used in the fuel cell vehicles.

However, the AC motors are difficult to control and they require AC controller separately

to regulate the power. But, AC motors are easily available in much bigger size and can

produce enough power to propel a vehicle.

2. Transmission of Fuel Cell Vehicles:

Transmission of Fuel Cell vehicles is much simpler than the transmission of conventional

vehicles. Engines create torque at relatively lower rates, which requires the transmission

to obtain the required level of torque to transmit to the wheels through driveshaft and

differential. However, in the electric vehicles the motor already produces torque at flat

and high rates therefore, simpler transmission is needed to transmit the power to the

wheels. Without a complex transmission, the mechanical losses generated in transmission

can be avoided and efficiency can largely be improved. Although, it does not need

heavier and complex transmission like in conventional vehicles but it still needs a fixed

gear system to give the optimum level of power when required during climbing or at

higher working conditions.

3. AC Motor Controller:

AC motor requires a controller, which regulates and actuates the motor according to the

Page 10: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

10  

power demand of the vehicles. It also serves as actuator for the pedal control and sends

information to the motor to produce require torque and power when a driver pushes the

acceleration pedal. AC motor controller is also responsible for generating power from

regenerative braking. When vehicle is applied brake to stop the heat generated in the

wheel is transformed to DC power that is processed through AC Motor Controller.

4. Regenerative Braking:

Regenerative braking is the process of braking a vehicle to complete without the loss of

energy applied during the braking system. When the barking is applied to a vehicle the

kinetic energy of vehicle is transformed to another form and stored to be used for later

use. When a conventional vehicle applies brakes all the energy is transmitted to the heat

and thermally dissipated. Since the motor can produce power and simultaneously can be

used to generate power. As soon as the brake is applied the controller sends signals to the

ultra capacitor that automatically connects to the generator (motor) to insert load on

generator. The motor is connected to the wheels and when the ultra capacitor put load on

the generator it start-generating power from braking as the wheels are still spinning.

5. Ultracapacitors:

Ultracapacitors are used in fuel cell vehicles in addition to the batteries to store electrical

power. When the power is produced from the regenerative braking it is generated in

matter of few seconds and that power has to be immediately stored in some form.

Batteries cannot store that power so fast; therefore, the ultracapacitors is the new

technology, which has the answer to this problem. Ultracapacitors can store the fast-

generated electric power produced in extremely short time7. There are few advantages of

ultracapacitors, which can challenge the batteries. First, the rate of storing the electrical

energy is very high and secondly, the power density of the ultracapacitors is high too.

This adds into the more power storage in a smaller sized storage as compared to the

conventional batteries. Moreover, the ultracapacitors have higher life cycle and carries

less weight8. This less weight can also improve in efficiency of the vehicle as motor has

to do less amount of work to propel the lighter vehicle. In fuel cell vehicles, when

regenerative power is produced the AC controller regulates the ultracapacitors to open the

connection and connects with the motor. At this particular point the motor works as a

generator in which, the generator is loaded that starts generating power and that power is

Page 11: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

11  

transmitted and stored in ultracapacitors.

 Figure  4:  Basic  operation  of  Fuel  Cell  Vehicles.  Process  Flow  and  Basic  Devices  used  in  the  Fuel  Cell  Source:  Sam  Glidden,  Jared  Delahanty  –  Graduate  Project,  Hydrogen  Fuel  Cell  Vehicles  –  The  Future  of  Transportation  

As shown in this above figure, an overall working of the devices used in the fuel cell

vehicles is presented. The green storage tanks in which, the hydrogen is stored or fed into

it from the any source. Oxygen is taken from the air by the help of the air pump;

afterwards, the air is filtered through filters to block any kind of additional particles.

Page 12: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

12  

Oxygen from air and hydrogen from the storage tank is allowed for the chemical reaction

in the fuel cell stacks. Electricity is generated in the fuel cells and transmitted to AC

controller and ultracapacitors simultaneously. Since the power produced by the Fuel Cell

is in DC. Therefore, it is converted to the AC and passed to the AC motor which, further

supplies power to the wheels through fixed gear drive. Also, there is another line going

back to ultracapacitors through the AC controller. This line transmits power back to

Ultracapacitors when generated during the regenerative braking.

6. Hydrogen Production: Most of the hydrogen is produced from the hydrocarbons or fossil fuel. Hydrocarbons are

composed of H2 hydrogen and Carbon, during the process of producing the hydrogen the

hydrocarbons are decomposed into hydrogen and carbons. Hydrogen is stored for the

usage for power generation and carbon is released into our environment.

The released carbon in atmosphere later combines with oxygen to form carbon dioxide.

Though this process of generating the hydrogen is cheaper but the it is not clean process

at all. At this point in time, more focused attention is being given to the clean production

Figure  5:  Process  of  Generating  Hydrogen  Gas  by  the  Electrolysis  of  the  Water  Source:http://www.instructables.com/files/orig/F4A/54HN/F5R8MQ53/F4A54HNF5R8MQ53.gif  

Page 13: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

13  

of hydrogen despite being its costlier process. The cleanest process of getting hydrogen is

by the electrolysis of the water.

7. Hydrogen Storage for Fuel Cell Vehicles: Hydrogen is extremely light gas; thus, it has to compressed at really high pressures and

stored in extremely high strength tanks. So, that in case of collision or accident the tanks

must not be ruptured. Hydrogen does not need spark to get ignited, the only thing it needs

get ignited is the oxygen from the atmosphere and it will blow off the tank. So far,

hydrogen is stored in the following three ways.

• Metal Bounded Hydrogen

• Liquid Hydrogen

• Carbon Nanotubes

1. Metal Bounded Hydrogen Storage:

The high-pressurized hydrogen gas or liquid hydrogen is not safe in case of collision. In

metal bounded hydrogen, the hydrogen is heated and merged with the metal. This makes

it safer to be used for vehicular application as it does not blows off the tanks even if the

tanks get ruptured during collision. The only downside of using this technology for the

storage of hydrogen is the cost of the process9. The process is relatively costlier and while

heating the hydrogen to bound with the metal, the overall efficiency of the fuel cell

vehicle reduces down considerably. Therefore, if the cost is major factor than metal

bounded hydrogen is not preferable to use as storage.

2. Storing Hydrogen as Liquid:

To store hydrogen as liquid, it has to be cooled down to 20 K10 above absolute

temperature so that it should not evaporate in the atmosphere. It takes huge amount of

energy to get this temperature range. Therefore, in this process the cost and efficiency is

affected.

3. Hydrogen storage in Carbon Nanotubes:

Hydrogen can be stored in Nano-scaled carbon. There have been several claims that

hydrogen can be stored in carbon nanotubes obtaining 50wt% hydrogen11. Still this

process is in early stage of development. It would take time to get matured and can be

used practically in the fuel cell vehicles.

Page 14: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

14  

8. Conclusion: Fuel Cell Technology for Automotive Application can bring a positive change towards

transportation industry by solving the environmental problems and at the same time

providing safe and sustainable medium of transport. Since, the process involved direct

conversion of chemical energy to electrical energy, it has considerably higher efficiency

than the convention vehicles. Moreover, the simplicity of transmission system can add

more efficiency to the system. Another positive side of fuel cells is that the motor

efficiency is much higher the internal combustion engine (ICE). The ICE have the lower

efficiency as much as 20 – 25 percent whereas, the motor efficiency can as much 90 %.

Hydrogen is clean, plenty in nature and renewable source of fuel. Currently the only

problem is optimizing the technology and get and store the hydrogen in a cheap and safer

mode. With the advancement of technology, there is a great hope that there would be

major breakthrough in the future in getting the hydrogen and easily be used for storage

and power up the vehicles.

Page 15: Fuel Cell Vehicles

Fuel  Cell  Science  &  Technology  –  ME  6580      

Khalil  Raza  –  Wright  State  University  

15  

9. Reference                                                                                                                1    Fuel  Cell  -­‐  http://en.wikipedia.org/wiki/Fuel_cell  2    Fuel  cell  –  From  Chemical  Energy  to  Electrical  Energy  -­‐  http://www.britannica.com/EBchecked/topic/221374/fuel-­‐cell    3  Types  of  Fuel  Cells  -­‐  http://www.fchea.org/index.php?id=44    4  Direct  Methanol  Fuel  Cells  Systems  -­‐  DMFC  http://www.fuelcellmarkets.com/fuel_cell_markets/direct_methanol_fuel_cells_dmfc/4,1,1,2504.html    5  Phosphoric  Acid  Fuel  Cell  Technology  http://www.fossil.energy.gov/programs/powersystems/fuelcells/fuelscells_phosacid.html    6  Types  of  Fuel  Cells  -­‐  http://www.britannica.com/EBchecked/topic/221374/fuel-­‐cell    7  2004,  Sam  Gliden  and  Jared  Delahanty,  Hydrogen  Fuel-­‐Cell  Vehicles,  The  Future  of  Transportation.  8  John  M.  Milter,  Natural  Science  –  Ultracapaciotrs  challenge  the  battery  http://www.ec-­‐central.org/kfi/files/Ultracap-­‐%20World%20&%20I%20-­‐%20June%202004.pdf    9  2007  Billur  Sakintuna,  Farida  Lamari-­‐Darkrim,  Michael  Hirscher,  “Metal  hydride  materials  for  solid  hydrogen  storage:  A  review.”  International  Journal  of  Hydrogen  Energy.  10  Takuji  Hanada  and  Kunihiro  Takahashi  Liquid  Hydrogen  Storage,  Energy  Carries  and  Conversion  Systems  Vol  –  II,  Liquid  Hydrogen.  11  Hydrogen  Storage  –  Carbon  Nanotubes  http://en.wikipedia.org/wiki/Hydrogen_storage#Carbon_nanotubes