Liquid Rocket Engine

Liquid Rocket Engine ##
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A liquid-propellant rocket or a liquid rocket is a rocket
engine that uses propellants in liquid form. Liquids are
desirable because their reasonably high density allows the
volume of the propellant tanks to be relatively low, and it is
possible to use lightweight centrifugal turbopumps to pump
the propellant from the tanks into the combustion chamber,
which means that the propellants can be kept under low
pressure. This permits the use of low-mass propellant tanks,
resulting in a high mass ratio for the rocket.
An inert gas stored in a tank at a high pressure is
sometimes used instead of pumps in simpler small engines
to force the propellants into the combustion chamber. These
engines may have a lower mass ratio, but are usually more
reliable 186,187 and are therefore used widely in satellites
for orbit maintenance.