Engines Machines
A rocket engine is a type of jet engine that uses only stored rocket propellant mass for forming its high-speed propulsive jet. Rocket engines are reaction engines, obtaining thrust in accordance with Newton's third law. Most rocket engines are internal combustion engines, although non-combusting forms (such as cold gas thrusters) also exist. Vehicles propelled by rocket engines are commonly called rockets. Since they need no external material to form their jet, rocket engines can perform in a vacuum and thus can be used to propel spacecraft and ballistic missiles.
Compared to other types of jet engines, rocket engines are by far the lightest, and have the highest thrust, but are the least propellant-efficient (they have the lowest specific impulse). The ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket engines become more efficient at high velocities, due to greater propulsive efficiency and the Oberth effect. Since they do not require an atmosphere, they are well suited for uses at very high altitudes and in space
Rocket engines become more efficient at high velocities, due to the Oberth effect.
Compared to other types of jet engines, rocket engines are by far the lightest, and have the highest thrust, but are the least propellant-efficient (they have the lowest specific impulse). The ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket engines become more efficient at high velocities, due to greater propulsive efficiency and the Oberth effect. Since they do not require an atmosphere, they are well suited for uses at very high altitudes and in spaceRocket engines become more efficient at high velocities, due to the Oberth effect.
Rocket engines produce thrust by the expulsion of an exhaust fluid that has been accelerated to high speed through a propelling nozzle. The fluid is usually a gas created by high pressure (150-to-2,900-pound-per-square-inch (10 to 200 bar)) combustion of solid or liquid propellants, consisting of fuel and oxidiser components, within a combustion chamber. As the gases expand through the nozzle, they are accelerated to very high (supersonic) speed, and the reaction to this pushes the engine in the opposite direction. Combustion is most frequently used for practical rockets, as high temperatures and pressures are desirable for the best performance.
A model rocketry alternative to combustion is the water rocket, which uses water pressurized by compressed air, carbon dioxide, nitrogen, or any other readily available, inert gas. Rocket technology can combine very high thrust (meganewtons), very high exhaust speeds and very high thrust/weight ratios (>100) simultaneously as well as being able to operate outside the atmosphere, and while permitting the use of low pressure and hence lightweight tanks and structure. More details
