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Fuel From Fresh Air

We all know that fossil fuel reserves are depleting and that causes prices to rise. Furthermore, the spectre of climate change means that there is real pressure to reduce CO2 emissions. Both of these factors combine to make the search for an alternative fuel source for our vehicles ever more urgent.

We all know that fossil fuel reserves are depleting and that causes prices to rise. Furthermore, the spectre of climate change means that there is real pressure to reduce CO2 emissions. Both of these factors combine to make the search for an alternative fuel source for our vehicles ever more urgent. Hybrids are now pretty mainstream but they still rely heavily on their internal combustion engines. Pure electric vehicles so far have very real limitations. Their range is extremely poor, they take too long to recharge and they are expensive. Hydrogen fuel cells are promising. They have a range and refuelling profile that is similar to conventionally fuelled vehicles but extraction of the necessary hydrogen is complex and expensive. Now, however, engineers are proposing an alternative power source that is so plentiful it is all around us; air.
 
Specifically, they are looking at liquid air. That is air that has been cooled to minus 196 degrees centigrade. This has been done before. A company in Boston, USA, managed to demonstrate a car running on liquid air as far back as 1902. The technology for liquefying air is mature too and it is used in many industrial processes. The idea is pleasingly simple. Liquid air expands rapidly when exposed to ambient temperatures, with one litre of liquid air expanding to 700 litres of normal gaseous air at room temperature. This rapid expansion can then be used to drive turbines or push pistons in an engine. The by product is simply air, so as it is used up and vented there is absolutely no pollution at all.
 
Clearly the air has to be liquefied first but this is not a prohibitively expensive process. Using current electricity prices as a guide, it would cost approximately 3p to create a litre of liquid air. There are other associated costs such as transporting and storing the air but these could reduce with economies of scale. The energy obtained from such an engine would be hard pressed to match the range of a conventional petrol car but it could outperform electric cars. It also has other benefits over electric cars, such as quick refuelling and the absence of complex and expensive batteries. Liquid air also provides a simple and effective method of storing energy from renewable sources, such as wind, which is often produced at a time when it is not needed. Clearly there is a long way to go with liquid air technology but its simplicity makes it an attractive proposition to explore.

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