Transit Buses: Today's Pioneers in Fuel Cell Transportation
While many believe that fuel cell transportation exists only in a place called the future, think again. Since 1994-1995, three fuel cell buses have been operating in Washington, DC, California, and Florida. Since 1998 and 2001, two second-generation fuel cell transit buses have been fabricated and tested to demonstrate commercial feasibility. The five buses serve as pioneering research, development, and educational test beds. They have demonstrated that fuel cell technology is viable, bringing fuel cell transportation in the United States closer to commercial realization.
It is also beneficial. Fuel cell transportation offers far-reaching advantages as a cleaner, quieter, more-efficient alternative to the combustion of gasoline and other fossil fuels. It could help address concerns about energy security, global climate change, and air quality.
Fuel Cell Benefits
Fuel cells offer the following advantages:
- Potential for extremely low emissions
- Less maintenance than conventional diesel or gasoline buses
- Reduce the nation's dependence on imported oil
Fuel cells first provided electricity and fresh water in the 1960s Gemini and Apollo space programs that led to putting man on the moon. Today, they are forging a new terrestrial path. The experience gained and lessons learned from these buses will help promote the use of fuel cells in other modes of transportation as well. The U.S. Department of Energy (DOE) Hydrogen, Fuel Cells, and Infrastructure Technologies (HFCIT) Program is working closely with the Vehicle Technologies Office to further the state of the art of fuel cell systems for highway vehicles.
While scientists and industry continue to make breakthroughs, several technical challenges for automotive fuel cell power systems remain:
- Lowering component and system costs,
- Developing high-volume manufacturing capability,
- Demonstrating component and system durability,
- Reducing system startup time (especially for gasoline-powered fuel cell systems),
- Developing high-efficiency air management subsystems.
Why Transit Buses?
Transit buses are ideal for pioneering fuel cell technology in transportation because
- Their compatible weight and volume constraints are amenable to today's fuel cells.
- Central fueling stations minimize fuel logistic issues.
- Structured routes and maintenance for fleets allow quantification of operational and cost issues.
- Fuel cell power requires no operational concessions with transit bus routine operations.
- The buses provide immediate environmental benefits to urban air quality because of their reduced emissions.
- They serve as full-sized operational laboratories to resolve technical issues hindering automotive use.
- They offer a first-hand opportunity for the public to learn about fuel cell technology.
Route to Acceptance
The quickest route to widespread acceptance of fuel cell transit buses dictates the use of a liquid fuel. A decade ago, the Federal Transit Administration (FTA) began a program to accelerate the introduction of liquid-fueled, fuel cell transit buses by placing vehicles into the hands of transit operators as soon as possible. The FTA chose Georgetown University, DOE, and Argonne National Laboratory as the program management team to develop these buses.
"Georgetown University has been a leader in the development of transportation fuel cells for over two decades. Over that span, the goal of commercial introduction of the technology never wavered," remarks Jim Larkins, Program Manager, Advanced Vehicle Development, Georgetown University. "The vehicles produced to date under the FTA-initiated program have provided knowledge and inspiration that have directly influenced the subsequent increase in fuel cell vehicle developments around the world."
For the initiative, the team selected methanol as the best near-term liquid fuel. Methanol has a well-defined chemical formula (CH3OH), can easily be reformed with a state-of-the-art high- or low-temperature steam reformer, will reduce oil imports, can be derived from renewable resources, and can be acquired in quantity at a reasonable price.
"As a hydrogen carrier, methanol greatly exceeds the on-board vehicular weight percent storage targets for hydrogen set by DOE. Coal, an abundant U.S. domestic fuel, can be used to produce methanol. The potential to make domestic coal the feedstock for transportation fuel cannot be ignored. This offers a realistic approach to true energy independence," explains Larkins.
In addition, transit agencies have already experimented with methanol-fueled internal combustion engines to power inner-city transit buses. Through this experience, they have found that the logistics of obtaining, storing, or handling methanol are not an issue.
"With this program, we're at the forefront of developing a fleet of longer-range, liquid-fueled fuel cell vehicles. No one else has used a non-hydrogen fuel and done so with a relatively small investment from the government," observes Bob Wimmer, previous Program Technical Director, Georgetown University, and now Research Manager, Technical and Regulatory Affairs, Environment, Toyota Motor North America, Inc.
Initially, researchers chose phosphoric acid fuel cell (PAFC) technology for the program because of its commercial legacy in electrical utility application and proven capability to operate on reformed fuel. However, the stable of fuel cell technologies has since been expanded to include proton exchange membrane fuel cell (PEMFC) and solid oxide fuel (SOFC) technologies (the latter for auxiliary power units for light- and heavy-duty vehicles) because of the significant progress recently achieved. PEMFCs hold the promise of becoming a robust, lightweight, cost-effective automobile power plant with attractive operational advantages, while the SOFC offers particular advantages in eliminating idling of diesel bus and truck engines.
Developing a fuel cell bus requires a strong interdisciplinary effort. Expertise in automotive and mechanical engineering, chemistry and electrochemistry, and chemical engineering is needed. In addition, a fuel cell generates electrical power that is used in an electric drive, which requires electrical engineering and power electronics expertise. All of these systems are computer-controlled, requiring expertise in computer science and control architecture. The fundamental aspects of corrosion and materials issues within the system bring materials scientists into the mix. The safety aspects of the vehicles include some areas of civil engineering as well. The team tapped into all of these areas of expertise to develop three 30-foot, first-generation, "proof-of-concept" buses, then two 40-foot, second-generation buses.
Generation I Buses
In spring 1994, Georgetown delivered the first of three, 30-foot fully compliant transit buses; the following two were rolled out in 1995. These methanol-fueled buses are called test bed buses (TBBs). Each TBB uses a 50-kW PAFC as the main power source, supplied by Fuji Electric, using technology licensed from Engelhard Corporation of New Jersey. All three vehicles are still operating as research, development, and educational test beds for automotive fuel cells. One is being tested at Georgetown University; another is at the University of California, Davis; and the third is at the University of Florida.
"The research we conduct applies to both the Generation I and Generation II buses developed at Georgetown University," remarks Dr. Paul Erickson, Assistant Professor of Mechanical and Aeronautical Engineering and Director of the Hydrogen Production and Utilization Laboratory at the University of California, Davis. "The buses serve as powerful research tools for providing data and model validation. We can actually look at the systems and get into them.
"By doing so, we found that there's quite a bit more we need to understand about the whole system used in the fuel cell buses — along with proving the reliability, lifetime, etc. We still have some technological hurdles to overcome and need a lot more experience in developing and operating the buses. And there really is a dearth of experts who are knowledgeable about this technology."
He continues, "One of our main goals at the University of California, Davis is to prepare engineers, technicians, and scientists about the hands-on problems and actual benefits we encounter in operating a fuel cell vehicle. We can have a large impact on the future success of the technology by familiarizing users and the public about the benefits as well as the limitations of fuel cell technology."
Erickson reiterates the benefits: Fuel cell vehicle technology provides clean, quiet, and energy-efficient transportation. It may allow the United States to diversify its national energy portfolio and thus enhance energy security by permitting greater use of domestic fuels in the transportation sector. However, issues that still need to be resolved regarding fuel cell technology include its current cost, low-temperature operation, and hydrogen production and storage.
While low-temperature operation may seem to be an advantage, he notes that the removal of heat from the vehicle with a small temperature difference becomes problematic, and general thermal management is complex. Low temperature also exacerbates the effect that fuel impurities can have on the fuel cell. In addition, there is a need for further research into hydrogen storage and production. The physical characteristics of hydrogen make it difficult to store in large enough quantities for a reasonable range with reasonable volume or weight for a vehicle. This results in a limited range for vehicles using hydrogen. Hydrocarbon fuel storage and subsequent onboard reformation is an attractive alternative because of the high energy densities associated with hydrocarbon fuels that overcome the range problem with hydrogen storage. However, onboard reformation does complicate the already complex fuel cell system by requiring a fuel processor and subsequent cleanup of the hydrogen stream.
Generation II Buses
In addition, two completely functional, 40-foot fuel cell transit buses have been fabricated and tested within the program to demonstrate commercial feasibility. This program drew on the experience and knowledge gained during the Generation I Program. Traction batteries provide surge power and a means to recapture kinetic energy from the buses through regenerative braking. The buses seat 40 passengers, meet every performance requirement of the transit industry, are extremely quiet, and travel approximately 350 miles between refuelings. The use of a liquid fuel allows for rapid conventional fueling.
Delivered in 1998, the first bus uses a derivative of a UTC Fuel Cells (formerly International Fuel Cells) PC25 utility power plant. The 100-kW PAFC-powered bus was demonstrated at the American Public Transit Association Bus Show in Phoenix, Arizona.
The second bus, introduced in 2001, is the first and only urban transit bus powered by a liquid-fueled 100-kW PEMFC. Developed by Ballard Power Systems, this PEMFC is the world's largest capable of operating on liquid fuel.
The Generation II buses represent a significant leap ahead of the Generation I buses for several reasons:
- Improved fuel cell power density: The fuel cells in the Generation II buses produce twice the power of the Generation I systems (100 kW compared with 50 kW), but the power plants weigh approximately the same (~4,000 pounds).
- More responsive fuel cells: The fuel cells in the Generation II buses can respond to the driver's power demand about 100 times faster (~20 kW/sec) than the Generation I buses.
- Improved life expectancy: It is anticipated that the newer fuel cells will have a life expectancy of 25,000 hours, about five years of transit bus operation (however, this is yet to be verified by testing.
Dr. James Fletcher, who has worked with the buses at Georgetown University, University of Florida, and dbb Fuel Cell Engines, notes that all five buses are still operational. He says, "The bus development program has been highly successful and has provided a strong fundamental understanding of fuel cell vehicles, both for industry as well as academia. It has helped focus the research and development effort towards the goal of efficient, reliable and robust operation."
Full-Scale Vehicle Demonstrations, Testing, and Analysis
Demonstrations are key to convincing potential customers that technology is fast approaching practicality, but it is vital to get operating test results to guide future developments. Controlled tests have provided quantitative and qualitative data on bus performance, noise and vibration levels, and emissions of regulated pollutants.
Emission testing of the 40-foot PAFC fuel cell bus was conducted in fall 1999 at the Environmental Technology Centre in Ontario, Canada. The test facility consisted of a computer-controlled, heavy-duty chassis dynamometer and a high-flow exhaust dilution tunnel. The results show that steady-state fuel cell emissions are well below both present and future heavy-duty vehicle emission requirements. They agree well with measurements taken at UTC Fuel Cells during the laboratory testing of the bus power plant and are consistent with their stationary power plants from which the bus system was derived.
|Fuel Cell Power||CO||NMHC||NOX||PM|
|Present CARB Standards||15.5||1.20||2.0||0.05|
|2007 CARB Standard||5.00||0.05||0.20||0.01|
|* In g/bhp-hr
The 40-foot PEMFC bus recently completed a similar test program at the Environmental Technology Centre. Results are now being analyzed and will be available in December 2003.
In the future, the team plans to develop an advanced, Generation III fuel cell bus with
- A PEMFC power plant
- Offers at least 240-kW power capacity and 50 kW/sec response rate to handle dynamic requirements
- Weighs approximately 4,500 pounds
- Provides quick first start capability (under 15 minutes)
- A nonhybrid fuel cell power system that
- Operates on methanol
- Significantly reduces weight
- Simplifies control scheme
- Improves over-the-road capability
- A 40-ft, low-floor bus platform, which is preferred in the U.S. transit bus industry
- Curb weight that approximates a comparable, compressed natural-gas-fueled bus
|Characteristic||Generation I||Generation II IFC Fuel Cell Bus|
|Vehicle type||BMI 30-ft Transit Bus||Nova BUS RTS Wide Front Door|
|Curb vehicle weight||25,500 lbs||39,500 lbs|
|Propulsion||Phosphoric acid fuel cell/battery hybrid||Phosphoric acid fuel cell/battery hybrid|
|Suspension (front and rear)||Air Spring, kneeling||Air spring, kneeling|
|Drive motor||DC Brush||AC Induction|
|Motor power||120 kW (160 hp)||186.5 kW (250 hp)|
|Top speed||55 mph||66 mph|
|Range||200-250 miles||350 miles|
|Noise level||10 db below internal combustion engines||10 dB below internal combustion engines|
For more information, visit Georgetown University's fuel cell bus web site.