Will liquid air be the fuel of the cars of the future?

Will the cars of the future drive with hydrogen tanks powering fuel cells, or with liquid nitrogen tanks? What is certain is that this last possibility, already considered in the 19th century, is being considered very seriously at this time.

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There is regular talk of advances in technology to safely store hydrogen to power various electrical devices. In recent years, there have also been announcements about miniature fuel cells that can be used for computers, cars, etc. Hydrogen is therefore presented as the energy source of the future, or more accurately the secondary energy source. Indeed, it is always necessary a primary source of energy, usually electricity, if possible produced from the light of the Sun. So it is expected that it will not really be hydrogen, but solar energy that will replace oil in a few decades.

The liquid air engine, a century-old concept
However, companies such as Highview Power Storage and Ricardo are now looking a little closer at an alternative to hydrogen already under consideration at the end of the 19th century: liquid air. Thus, in the 1890s, Charles Tripler had succeeded in convincing several investors that his air liquefaction process could allow energy to be stored in this form at a lower cost. As he had shown, it was possible to then power steam engines with this liquid air by letting it relax. Unfortunately, Tripler had exaggerated the efficiency of the conversion with its process, and investors' hopes were dashed.

The idea has been resurfaced for some time now. For example, cars have been developed that operate not with liquid air, but with compressed air. However, several groups such as Messer intend to return to the concept of a secondary energy source in the form of liquid air, or more precisely liquid nitrogen. One of the reasons is simple to understand. Liquid nitrogen does not naturally present the same risk of explosion as hydrogen.

Full of liquid nitrogen, please!

For now, Highview Power Storage's attempts have led to the development of a device with an energy conversion efficiency of 50-60%, while conventional batteries can reach 90%. Improvements are to be hoped for, but not to the point of competing directly with the batteries at this level.

However, this does not mean that liquid nitrogen is not a serious competitor for nickel-hydding metal batteries or lithium-ion batteries, which are used in hybrid cars in particular. Indeed, the density of energy storage is the same, and it is much easier and faster to redo a full of liquid nitrogen, even at -200 degrees Celsius, than to recharge batteries or batteries. Above all, liquid nitrogen storage systems can last for decades, while the battery life is only a few years.

Over time, prices may well be competitive. So, will we be rolling with liquid nitrogen tomorrow? It is likely that some of us will.

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