THE NATIONAL CLEAN BUS NETWORK
home || about ||   news  ||  the problem  ||  solutions  ||  clean bus fleets  ||  links  ||  comments

FUELS

fuels  ||  technologies  ||  regulation

HYDROGEN

Two propulsion technologies to utilize hydrogen are undergoing major development and demonstration. These are hydrogen fuel cells and hydrogen internal combustion engines.

Fuel Cells

Hydrogen fuel cells combine on-board hydrogen with oxygen in the air to generate electricity and water vapor. Fuel cells are about 40 to 60 percent efficient in converting energy, compared to about 20 percent efficiency for internal combustion engines. Fuel cells produce no harmful emissions, potentially eliminating vehicles as sources of air pollution.

Emissions of Hydrogen Fuel Cell (at the tailpipe) Compared to Petroleum Diesel[1]

Fuel cell technology for transit buses has been in the research, development, and demonstration stage for several years. In 1994, Georgetown University used methanol in one of the first demonstrations of fuel cell technology in buses. Since the late 1990s, the number of fuel cell demonstrations increased dramatically. Today, practically every bus manufacturer in North America and Europe is involved to some degree in fuel cell demonstrations.

Two large scale demonstration projects are already underway. The European Fuel Cell Bus Project will demonstrate 30 fuel cell buses in ten cities in full revenue service for two years. Delivery of these buses by DaimlerChrysler began in the Spring of 2003. Explaining Daimler Chrysler’s plan, Dr. Eckhard Cordes, head of commercial vehicle busines stated, “Urban bus transport is the ideal field for practically testing the fuel cell as a vehicle propulsion system.” Buses are part of a “niche” market where technical and other resources are centralized, making fueling, maintenance and problem-solving easier.The California Fuel Cell Partnership in 2002 began operation in November of its first fuel cell bus in revenue service in Thousand Palms, CA. California will receive six more fuel cell buses in 2004. 

Internal Combustion Engine (ICE)

The internal combustion engine model for a hydrogen propulsion system combines proven technology found in everyday cars and trucks with a cleaner-burning fuel. A hydrogen ICE can reach 38 percent efficiency, about 25 percent greater than a standard gasoline engine, and can achieve emissions with after-treatment devices that are below ambient conditions. Additionally, hydrogen is pure when it burns, so it does not release carbon dioxide.

The Department of Transportation and some engine manufacturers have expressed interest in demonstrating this technology in buses. The technology is quick to deploy, since little research and development is needed (relative to hydrogen fuel cells), and the emissions characteristics of the engine would allow it to meet federal emissions standards. Besides, the deployment of hydrogen-powered ICE vehicles creates demand for hydrogen refueling infrastructure, which will prepare the transportation market for even cleaner, more efficient hydrogen fuel cell vehicles when they become available. As of the summer of 2003 there have not been demonstrations of hydrogen ICE buses in full operational and revenue service. However, the Department of Transportation is working to organize some.

Renewable Vs. Non-Renewable Hydrogen

Though hydrogen is the most abundant element in the universe, it is not easily found in its pure form. Rather, it is bound up in combination with other molecules and must be separated from them. The water molecule provides one of the most abundant and accessible sources of hydrogen. However, the process of electrolysis, the separation of water into hydrogen and oxygen, requires electricity. The source of this electricity can come from any energy source, including nuclear, coal and others that pollute the air and water. Hydrogen is also abundantly found in hydrocarbon fuels, including natural gas and other petroleum products. However, the process of generating hydrogen from these products also produces unwanted emissions. The only known way to keep hydrogen fuel cells as truly renewable, non-polluting sources of energy is to ensure that hydrogen is generated through renewable means using solar, wind, geothermal, biomass and hydroelectric energy to drive electrolysis, or through controlled biological processes using enzymes and algae, for example. Hydrogen can also be captured as a by-product from industrial production process, as in steel and chemical manufacturing.