The principle of jet propulsion is based on Newton secondlaw and third law of motion Momentum is imparted to a mass of fluid in such a mannerthat reaction of the imparted momentum gives propulsiveforce This is done by expanding the gas which is at highertemperature and pressure through the nozzle so that thegas with increased velocity in form of jet comes out intothe atmosphere and its reaction in the opposite directiongive propulsive force
In turboprop engines, a portion of the engines thrust is produced byspinning a propeller, rather than relying solely on high-speed jetexhaust
Thrust force is generated by expelling mass (initially stored in thespacecraft) from the spacecraft at high velocity
They consist of three sections; an inlet to compress incomingair, a combustor to inject and combust fuel, and a nozzle toexpel the hot gases and produce thrust
Ramjets require a relatively high speed to efficiently compressthe oncoming air, so ramjets cannot operate at a standstill andthey are most efficient at supersonic speeds A key trait of ramjet engines is that combustion is done atsubsonic speeds. The supersonic incoming air is dramaticallyslowed through the inlet, where it is then combusted at the muchslower, subsonic, speeds The faster the incoming air is, however, the less efficient itbecomes to slow it to subsonic speeds. Therefore ramjet enginesare limited to approximately Mach 5
•They consist of an inlet, a combustor, and a nozzle•Scramjets do not slow the oncoming airflow to subsonic speedsfor combustion, they use supersonic combustion instead
•A turbojet engine is a gas turbine engine that works by compressingair with an inlet and a compressor (axial, centrifugal, or both),mixing fuel with the compressed air, burning the mixture inthe combustor, and then passing the hot, high pressure air through aturbine and a nozzle•The compressor is powered by the turbine, which extracts energyfrom the expanding gas passing through it. The engine convertsinternal energy in the fuel to kinetic energy in the exhaust,producing thrust.
A water jet, or pump jet, is a marine propulsion system thatutilizes a jet of water. The mechanical arrangement may be aducted propeller with nozzle, or a centrifugal compressor andnozzle.
A pulse jet engine (or pulsejet) is a type of jet engine in whichcombustion occurs in pulses. Pulsejet engines can be made withfew or no moving parts and are capable of running statically
It uses the gas generator core (compressor, combustor, turbine) toconvert internal energy in fuel to kinetic energy in the exhaust
Turbofans differ from turbojets in that they have an additionalcomponent, a fan Like the compressor, the fan is powered by the turbine section ofthe engine Unlike the turbojet, some of the flow accelerated by thefan bypasses the gas generator core of the engine and isexhausted through a nozzle Turbofans are generally more efficient than turbojets at subsonicspeeds, but they have a larger frontal area which generates moredrag
propulsive efficiency : how much of the energy of the jet ends upin the vehicle body rather than being carried away as kineticenergy of the jet
For jet engines: For rockets: Where v = velocity at which engine is movingve = exhaust velocity
Propulsion Performance is determined by ‘Specific Impulses’which permits an objective and comparative evaluation of thrustengines and propulsion systems of different designs and withdifferent propellants The most useful parameter for determining thrust engine (orthruster) performance is Thruster-specific ImpulseIsp = F / moThe Isp is defined as the impulse delivered per unit mass ofpropellant