Jet Engine vs Rocket Engine
The jet and rocket engines are reaction engines based on Newton’s third law. Rocket engine is also a jet engine with few specific variations between the two. The thrust of the two is from the speed of the exhaust of the engine. The exhaust of a rocket engine reaches the speed of sonic near the throat of the nozzle, and the expansion in the nozzle further multiplies the speed, giving hypersonic exhaust jet. The jet engine uses air and fuel for combustion, and operates at subsonic or sonic speeds. Jet engine only works in atmosphere, whereas rockets can operate in vacuum and in atmosphere. Jet engines take oxygen for combustion from the atmosphere but rockets have their own oxygen.
A rocket engine, or simply “rocket,” is a kind of jet engine that uses only propellant mass, which produces pressurized gas for forming its high speed propulsive jet that is directed through a nozzle to produce thrust in Rocket engines. Most of them are internal combustion engines, and instead of using external materials to form the jet they use the exhaust from the IC engines. The highest exhaust velocities of jets are from the rocket engines.
The principal of operation of the rocket engine is divided into three main components, and differ slightly with the type of propellant used. First is the propellant combustion or heating, which produces exhaust gas, second is, passing it through a supersonic propelling nozzle, which helps to accelerate the exhaust gas to high speeds using the heat energy of gas itself. Then the engine is pushed in the opposite direction, as the reaction to the exhaust flow. This gives better thermodynamic efficiency based on high temperatures and pressures. It is because at high temperatures the sonic speed too is very high. Sonic velocity is roughly proportional to the square of the temperature of the exhaust.
The construction of the rocket engine depends on the type of propellant use. Many engines are internal combustion engines, which use propellant masses of mixture of fuel and oxidizing components, or a combination of solid and liquid, or gaseous propellants. The other type is heating the chemically inert reaction mass using a high energy power source via a heat exchanger.
Jet engine consists of many parts such as a fan, compressor, combustor, turbine, mixer, and nozzle. The availability and the arrangement of these parts together with the drive mechanism give different types of jet engines. Engine sucks the air and compress it in the compressor. Then the compressed and heated air is sent to the combustor and mix with fuel and burn. The exhaust is sent to the turbine to produce the thrust to drive the engine.
The available types of the jet engines are: ramjet, turbojet, turbofan, turboprop and turbo shaft. The principal of operation of all the engines are similar with the following exceptions. In turbofan, a portion of compressed air is directly fed to the turbine. Although it is not heated as the exhaust from the combustor, it carries a high mass of air and thus, contributes to a larger portion to the total thrust. In turboprop and turbofan, the thrust is produced by a propeller too. In turbo fan, the total thrust is produced by a propeller as we can see it in the helicopters.
Jet Engine vs Rocket Engine
- Rockets are used for spacecrafts and missiles.
- The use of jet is mainly in the transport industry and can be found with military aircrafts, aircrafts, high speed cars, boats and ships too. Other uses are in cruise missiles and unmanned aerial vehicles (UAV).
- Rocket engine is least energy efficient to jet.
- The Noise pollution is higher with rocket engines compared with jet engines.
- The jet engines are more complex to rocket engines.