Chemical propulsion

Chemical propulsion

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The chemical propulsion engine is the most used in rockets. The chemical process that feeds it is the combustion of propellants.

While the propellant of a jet aircraft is composed of a single chemical component, the fuel that is burned by the oxygen that the engine extracts from the air, the propellant that feeds the engine of a rocket must have, in addition to the fuel, also an oxidant or oxidizer, that is, a chemical compound necessary to burn the fuel, because the rocket must fly mostly in the vacuum of space, where there is no oxygen.

Chemical propulsion rockets can be of two types: solid propellant and liquid propellant.

In solid propellant rockets, the fuel and the oxidant are mixed together in the form of a compact and solidified powder that accumulates in the combustion chamber by adhering perfectly to the walls and leaving a central cylindrical hole. One of the most commonly used combinations for solid propellants is the mixture of polyurethane, a plastic fuel, with ammonium perchlorate as an oxidant; although other mixtures are also used.

Liquid propellant rockets carry fuel and oxidant in two separate tanks. The two liquids are sent by means of a pump to the combustion chamber where, upon contact, they develop the chemical process that gives rise to a powerful flow of gaseous particles. One of the most commonly used combinations for liquid propellant rockets is that of liquid hydrogen (fuel) with liquid oxygen (oxidizer). Of this type were the engines of Saturn V, which took the Americans to the Moon.

A characteristic that differentiates solid propulsion rockets from chemical propulsion rockets is that, in the former, combustion and, therefore, thrust, lasts until the propellant exhausts; however in seconds it is possible to block it, interrupting the feed flow of the liquid propellant contained in the tanks, by means of a valve.

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