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Tuesday, September 19, 2017

Hydrogen as car fuel?

Posted by Krzysztof Lis on April 17, 2008

In this article we’ll think if it’s is possible and reasonable to use hydrogen as car fuel. I posted some time ago an article about hydrogen fuel car, this will be the second article on hydrogen.

Hydrogen was used as energy carrier for long time. It can be produced from plain water, and can be burnt in engines, burners or other devices to produce energy. But can hydrogen be energy source for automobile transport?

First of all, let’s state one important thing. Hydrogen is not an energy source! Wind, sun and rivers are energy sources. Natural gas, petroleum (crude oil), coal are energy sources. Hydrogen isn’t. Why? Because to make hydrogen, you need an energy of some kind. Hydrogen is not a fossil fuel, nor a renewable energy source… It’s similar to batteries, for example simple AA rechargeable cells. They don’t grow on trees and you can’t dig them out.

But hydrogen is an interesting way to store energy used for powering cars. Similar to rechargeable batteries or compressed air tanks. The energy has to be manufactured in some power plant, though.

Currently storing hydrogen is very difficult. Hydrogen particles are very very small and will escape from almost any tanks. This gas has very low energy content per unit volume, so it has to be compressed to very high pressures to make the tanks smaller. It can be stored in liquid state, but to achieve liquid phase the gas has to be cooled to extremaly low temperatures (below –250 °C / –420 °F). The tank would have to be criogenic to keep the gas cool. It can also be absorbed by some substances, for example metals, in metal hydrides. But metal tank needs to be cooled while being filled up (absorption produces heat) and heated when hydrogen is to be released. The latter is easy to do, because most engines produce warm exhaust gases. Metal tank would also be very heavy, compared to the amount of energy stored.

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