Whether it’s two-strokes or four, one cylinder or eight, the majority of the motors we use today are powered by the internal combustion of gas and air. Mixing gas and oxygen is not the only means to create the energy required to propel an aircraft. In fact, sometimes it’s the least effective option.
In the typical vehicle engine, power is created from the cylinders. Each cylinder has a shaft with a piston that goes down to draw in gasoline and air. The gas is triggered after the plug stops. Energy and the heat in the explosion drive the piston back down. Once the piston is pushed, it pushes against the pole, which moves the crankshaft. This technique works so well that it’s been replicated millions of times in everything from chainsaws to Ford F-150s.
Spaceships do not work the way vehicles work on the Earth
However, this ordinary way of generating energy relies on oxygen within the air. In the space, the reason nobody can hear you shout is, there’s no air (or oxygen).
Unlike a truck that has air available which can be drawn by it from its environment to carry its oxidizer, vehicles with rocket motors need to carry their fuel and propellant with them.
The Propellants come in two forms – composite and homogenous. In both types, the oxidizer and the fuel are stored when they are ignited, and electricity gets produced. Solid propellants are unique because fuel and the oxidizer exist as a single chemical jointly, or as nitrocellulose with nitroglycerine in them.
In case of solid propellants, the fuel and the oxidizer are separate materials which get mixed to form a powdery or a crystallized mix. It often contains ammonium nitrate or chlorate, or potassium chlorate (as the oxidizer), and some sort of a strong hydrocarbon fuel (like plastic or asphalt ).
There are three kinds of propulsion: cryogenic, petroleum-based and hypergolic. Until thrust is necessary, all three of those propulsion methods store fuels and their oxidizers individually. When rockets loaded with fuel and a liquid propellant are triggered, a little of each (fuel and oxidizer) is pushed into the combustion chamber, where they mix and burst, and as a result, they produce the essential power.
Petroleum-based liquid fuels, as the name suggests, mix a petroleum product (such as kerosene) with dissolved oxygen, which, being highly-concentrated, leaves an efficient and effective fuel. This method was used in Soyuz, in addition to the stages of IB Saturn I and V.
Highly effective but difficult to keep stored for the extended time period due to the need to maintain cold (hydrogen remains a liquid at -423F, and oxygen in -297F), cryogenic propellants are used only in limited applications. However, those include the critical engines of the Space Shuttles and specific phases of the Delta IV and a few of the Saturn rockets.
With both cryogenic and petroleum-based fuels, some ignition is needed either through chemical pyrotechnic or electrical means. Standard hypergolic fuels consist of various types of hydrazine (including unsymmetrical dimethylhydrazine and monomethylhydrazine), while nitrogen tetroxide is more often used as the oxidizer.
Liquid at room temperature fuel is easy to store, which makes them highly desirable for numerous applications in Maneuvering System.