Hydrogen as Fuel



Hydrogen atom

The most abundant energy vector in the universe, belonging to the family of Alkaline Metals, because it has 1 electron in the last layer, exists naturally in its molecular form.

In its most abundant isotope with one proton and one electron. At room temperature is a diatomic gas (combined with another hydrogen atom – H2), is flammable, colorless, odorless, tasteless, non-toxic -contudo asfixia-, is not corrosive -but reativo- highly water insoluble.

It is the second hardest substance to liquefy. Under atmospheric pressure this happens to 20,3K. It is the smallest element desidade when liquefied density is 1/14 of the density of water.

Hydrogen as fuel

The total energy released by combustion (LHV -P.C.I calorific value lower -Quantity of energy released in the form of thermal energy, in the oxidation of a fuel) per unit mass is the largest of all known fuels. For example, if a hydrogen burn grass will get 2.8 times more energy to burn the same mass of gasoline. This feature makes it the ideal propellants for rockets.

However, it is a fuel of low energy density per unit volume. For example, a liter of gasoline weighs 700g while a liter of liquefied hydrogen (temperature <20,3K) weighing ~ 71g. 350atm tablet weighs only ~ 30g.

These, among others, peculiar features make hydrogen as a fuel, have positive and negative aspects.


Positive aspects of hydrogen fuel

The main positive aspect of this fuel is that it produces energy without emitting carbon dioxide (CO2). Depending on the environment used, energy production is free of any pollutants. For example. If combustion of hydrogen occurs using air from the atmosphere, NOx production will occur. However, if low-temperature fuel cells (eg, PEMFC) are used, the production of electricity will have thermal and water by-products.

Negative aspects of hydrogen fuel

Hydrogen is not a primary fuel. This means that it is not available to be used directly. The problem is that there are more or less severe environmental impacts, as the method used to obtain it. The emission of CO2 is one of them. Another is that this process consumes energy. “Energy can neither be created nor destroyed, only transferred trasformada or” preached Joule, inspired by Antoine Lavoisier. This means that even with the high energy efficiency of fuel cells, we will have to expend more energy to fathered this form of fuel that will recover on its combustion.

Who saw some film of a rocket launch or the destination of the airship ‘Hindenburg’ know how it can be dangerous in an uncontrolled reaction. Of course, security codes transport and storage, as well as suitable recipient system tend to minimize this.

Another problem for its wide use is related to its logistics (transport, storage and distribution).

Eduardo Stefanelli

Engenheiro por profissão, professor por vocação

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