Types of Rocket Engines
All rocket engine produce thrust by accelerating a working fluid. But there are many different ways to produce the acceleration, and many different available working fluids.
The simplest rocket engine uses air as the working fluid, and pressure produced by a pump to accelerate the air. This type of ‘engine’ is used in a toy balloon or a stomp rocket. Since the weight of air is so small, this type of rocket engine does not produce much thrust. A bottle rocket uses water as the working fluid and pressurized air to accelerate the working fluid. The water is much heavier than air that the bottle rockets generate more thrust than stomp rockets.
Model rockets and most full scale rockets use chemical reaction rocket engines. Chemical rocket engines use the combustion of propellants to produce exhaust gases as the working fluid. The high pressures and temperatures of combustion are used to accelerate the exhaust gases through a rocket nozzle to produce thrust. Propellants are composed of fuel to be burned and an oxidizer, or source of oxygen, for combustion. Under normal temperature conditions, propellants do not burn, but require some source of heat, or igniter, to initiate combustion. Chemical rocket engines do not typically reply on the surrounding atmosphere as a source of oxygen. Thus, chemical rocket engines can be used in space, where there is no atmosphere present. (Most rockets that are sent to space use the chemical rocket engines, as they can be used in space).
There are two main types of chemical rocket engines; liquid rockets and solid rockets.
There are two main types of chemical rocket engines; liquid rockets and solid rockets.
In a liquid rocket, the fuel and the oxidizer are stored separately and pumped into the combustion chamber of the nozzle where the burning occurs. With a liquid rocket, you can stop the thrust by turning off the flow of fuel or oxidizer. Liquid rocket tend to be heavier and more complex because of the pumps used to move the fuel and oxidizer, and you usually load the fuel and the oxidizer into the rocket just before launch.
In a solid rocket, the fuel and the oxidizer are mixed together into a solid propellant which is packed into a cylinder. The propellant only burns on the surface. Once the burning start, it will proceed until all the propellant is consumed. With a solid rocket, you must destroy the casing to stop the engine. A solid rocket is much easier to handle and can sit for years before firing.
Another type of rocket engine is the nuclear thermal engine. In the nuclear thermal engine, a nuclear reactor provides a continuous source of heat which is used to accelerate the working fluid. The working fluid can be any gas which is heated as it is passed over through the reactor and exited through the nozzle. Nuclear thermal engines are being developed under Project Prometheus.
A new type of rocket engine is the electric engine, also known as an ion engine. The working fluid for an electric engine is composed of very many, but very small, charged particles called ions. The acceleration of the working fluid is produced by electrostatic forces, not by combustion. Ion engines produce very small amounts of thrust, but can produce thrust for a long period of time because the mass flow rates are very small.