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Hydrogen energy density as it relates to alternative fuel use . . .

Submitted by mutant_pie on August 14, 2008 - 3:01pm. Remember Outdoors

. . . is arguably best put in the Other Technology section, but this is sort of a continuation of the Solar Salvation topic in this forum. I found this site on aerospace tech that answered my question;

http://www.aerospaceweb.org/question/propulsion/q0170.shtml

In order to make a scramjet work, researchers must choose a fuel that can burn rapidly and generate a large amount of thrust. Hydrogen meets these criteria. ... (edited for space, MP)

There are also other advantages to using hydrogen as a fuel. First of all, hydrogen is extremely flammable; it only takes a small amount of energy to ignite it and make it burn. Hydrogen also has a wide flammability range, meaning that it can burn when it occupies anywhere from 4% to 74% of the air by volume. Since hydrogen is a gas, it mixes very easily with air allowing for very efficient combustion. Another advantage over hydrocarbon-based fuels like JP-8 or gasoline is that hydrogen does not produce any harmful pollutants like carbon monoxide (CO), carbon dioxide (CO2), or particulate matter during the combustion process. It is for this reason alone that many researchers have promoted hydrogen as a fuel in the public transportation industry.

Nevertheless, there are some disadvantages to using hydrogen as a fuel in aerospace vehicles. Hydrogen is not a dense fuel. At standard pressure and temperature, it has a density of only 0.09 kg/m3. Compare that to the density of gasoline at 750 kg/m3 or JP-8 at 800 kg/m3. While this low density is an advantage in terms of saving weight, hydrogen requires a large volume in order to store an adequate amount of chemical energy for practical use. Hydrogen gas is typically stored under pressure to increase its density, but even at 10,000 psi (68,950 kPa) it will contain only a quarter of the chemical energy stored in an equivalent volume of JP-8. The density of hydrogen can be further increased by cooling and pressurizing the substance to the point that it becomes a liquid, but even in this form it will need a tank approximately twice the size of that required by JP-8. (edited for space, MP)

So with liquified Hydrogen, you need a tank twice as big as a jet fuel, or other hydrocarbon.

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mmphosis's picture

pressure

Submitted by mmphosis on August 15, 2008 - 5:02pm.

I appreciate you posting.

A ramjet seems impractical for my purposes. I am looking at energy storage systems for small lightweight vehicles.

A compressed air vehicle seems like a viable option. I think they were invented in France, and are made in India. There is at least one company in the USA that is going to sell compressed air cars in two years from now. The system is relatively low tech and low cost.

One way to store a lot of hydrogen is in a large zeppelin. The advantage is that the vehicle floats. The disadvantage is that it is highly volatile.

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Jon's picture

I recently saw a video of Jay

Submitted by Jon on August 15, 2008 - 10:55pm.

I recently saw a video of Jay Leno demonstrating one of his steam cars. It burned gasoline, but there are many other fuels in a more modern design that can be built to heat the water. The car was 100 years old. However, it's interesting to think about how are are still a very steam-oriented world. most power plants are operated by fuel heating water into steam - only hydroelectric, wind, photovoltaic and a few others do not.

» I am not in this world to live up to other people's expectations, nor do I feel that the world must live up to mine. - Fritz Perls

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Heated water, heated hydrogen in a stirling engine

Submitted by mutant_pie on August 15, 2008 - 11:25pm.

Jon, you make an interesting point about the continued use of steam turbines. . .

There had been a discussion on this board awhile back about stirling heat engines. I'm grateful for the shared knowledge on this board. Because when I read that the current most advanced solar power generators were heating hydrogen gas as the medium inside a stirling engine, I knew to what they were referring. Apparently there is a big installation of these being set up in Arizona (I think).

Tata Motors is the indian company that has licensed the pneumatic powered engine for their cars. These will be kind of neat I think (small and clunky a little bit from the production art), but functional. Besides cleaning and tire pressure checking, the major maintenance required is changing out the 2 liters of vegetable oil that acts as a lubricant, once every 50,000 miles. Incredible pressure in the tanks. I wonder if that technology has any room for improvement?

Mutant_Pie

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