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Friday, January 8, 2010

Hydrogen Fuel

Why is hydrogen used as a fuel?

Hydrogen has the highest energy content per unit weight of any known fuel-52,000 Btu/lb (120.7 kJ/g). It burns cleanly. When hydrogen is burned with oxygen, the only by products are heat and water. When burned with air, which is about 68% nitrogen, some oxides of nitrogen are formed. The process of converting hydrogen to energy using engines or fuel cells is much more efficient than the comparable gasoline counterparts.

How much hydrogen is consumed to produce 1 kWh of electricity using a PEM fuel cell?

In general, to produce 1 kilowatt (kW) of electricity for 1 hour (one kilowatt-hour, kWh) from a proton exchange membrane (PEM) fuel cell requires about 25-27 standard cubic feet (scf) of hydrogen. A standard cubic foot (scf) is the amount of hydrogen that occupies one cubic foot of space when it is not pressurized (in other words, at regular atmospheric pressure) and at 60 degrees F (a little cooler than room temperature).

How does hydrogen compare with other fuels like gasoline and diesel?

• Hydrogen can be totally nonpolluting (water is the exhaust).
• Hydrogen can be economically competitive with gasoline or diesel.
• Hydrogen can be as safe as gasoline, diesel, or natural gas.
• Hydrogen can help reduce our dependence on imported fuels.
• Hydrogen can be produced in any country or locale from a variety of energy sources.

What is the octane rating of hydrogen?
Short answer: "130+" according to a study done by the College of the Desert and Sunline Transit Agency

Longer answer: The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes "knocking" in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting compared to higher octane grades (like "super" 93-octane gasoline).

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that for gasoline, it costs more.

Hydrogen has an octane rating of 130 because it can be compressed more than gasoline and 100% octane before the fuel automatically ignites in the engine. (Gasoline with 87-octane has 87% octane, a special kind of hydrocarbon that makes up gasoline and other fuels).

Here are some other octane ratings:
• Methane: 125
• Propane: 105
• Octane: 100
• Gasoline: 87
• Diesel: 30

How is hydrogen produced?

Hydrogen is the most abundant element in the universe. However it is always bonded with something else like oxygen (to make water) or carbon (to make all plants). Hydrogen is all around us, but to use it, we must first separate the hydrogen from the other things bonded to it. One of hydrogen's advantages is that it can be made from a variety of local resources like water, plants, coal, natural gas and even algae. Although having so many choices sounds complicated, it's a great advantage because no one region or country has to be dependant on one resource. This means you can choose whichever resources make the most sense to make hydrogen, environmentally and economically.

Another choice that you have when making hydrogen is how much you make. When we make most fuels today, it's best to make very large quantities in refineries. However, with hydrogen you can just as easily make very small amounts, enough for one camera or cell phone, or very large amounts that could supply an entire town.

Today, in the U.S., over 95% of the hydrogen is made in very large quantities from natural gas, mostly to make fertilizer and to help make gasoline cleaner by removing impurities like sulphur. As hydrogen moves from these large industrial uses to something that you and I commonly use to fuel our businesses, homes, electronics and vehicles, we expect other resources besides natural gas to be used and that it will be made in a variety of amounts depending on how much is needed.

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