SCRAM JET ENGINE

BY

K.LOKESH

15311A0349

MECH-A

SNIST.

JET ENGINE

A jet engine is a reaction engine discharging afastmoving jet that generates thrust by jet propulsion.

CLASSIFIED AS:

》Airbreathing jet engines :

turbojets, turbofans, ramjets, and pulse jets and

》Non-Airbreathing jet engines :

rocket engines.

》In general,jet engines are combustion engine.

》These typically feature a rotating aircompressor powered by a turbine, with the leftover power providing thrust via a propelling nozzle — this process is known as the Brayton thermodynamic cycle.

Air is compressed by the compressors and fuel is

injected for combustion and high speed jet is

produced.

The key to a practical jet engine was the gas turbine, used to extract energy from the engine itself to drive the compressor.

RAM JET》A Ramjet, sometimes referred to as a flying stovepipe or an athodyd(an abbreviation of aero thermodynamic duct), is a form of airbreathing jet engine that uses the engine's forward motion to compress incoming air without an axial compressor.

It uses subsonic flow of air for combustion.

》Ramjets cannot produce thrust at zero airspeed, they cannot move an aircraft from a standstill.

》A ramjet-powered vehicle,therefore, requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust.

Subsonic, Supersonic & Hypersonic Flight

where M is mach number

u is flow velocity of vehicle

M=u/c c is speed of sound in surrounding

mediumIf M <0.8, subsonic

0.8<M <1.2,transonic

1.2 <M <5.0, supersonic

5.0<M <10.0,hypersonic

10.0 <M <25.0, high hypersonic

M> 25, Rentry speed.

SCRAM JET

》A Scram(supersonic combusting ramjet) is a variant ofa ramjet airbreathing jet engine in which combustion takes place in supersonic airflow.

》As in ramjets, a scramjet relies on high vehicle speed toforcefully compress the incoming air before combustion (hence ramjet).

》but a ramjet decelerates the air to subsonic velocities before combustion, while airflow in a scramjet is supersonic throughout theentire engine.

》This allows the scramjet to operate efficiently at extremely high speeds.

DESIGN PRINCIPLES

The scramjet is composed of three basic components:

◆a converging inlet, where incoming air is compressed;

◆a combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat; and

◆a diverging nozzle, where the heated air is accelerated to produce thrust.

》Unlike a typical jet engine, such as a turbojet or turbofan engine, a scramjet does not use rotating, fan-like components to compress the air; rather, the achievable speed of the aircraft moving through the atmosphere causes the air to compress within the inlet.

》Therefore no moving parts are needed in a scramjet.

》Scramjet engines operate on the same principles as ramjets, but do not decelerate the flow to subsonic velocities.

》Rather, a scramjet combustor is supersonic: the inlet decelerates the flow to a lower Mach number for combustion, after which it is accelerated to an even higher Mach number through the nozzle.

》This deceleration, which is produced by a normal shock, creates

a total pressure loss which limits the upper operating point of a

ramjet engine.

》Depending on the fuel, the kinetic energy of the air and the

potential combustion heat release will be equal at around Mach

8.

VEHICLE PERFORMANCE

specific

impulse is

change in

momentum per

unit of

propellant .

OVERALL ENGINE EFFICIENCY

ADVANTAGES

1. Does not have to carry oxygen.

2. No rotating parts makes it easier to manufacture than a turbojet.

3. Has a higher specific impulse (change in momentum per unit of propellant) than a rocket engine; could provide between 1000 and 4000seconds, while a rocket typically provides around 450 seconds or less.

4. Higher speed could mean cheaper access to outer space in the future.

Disadvantages

1. Difficult / expensive testing and development.

2. Very high initial propulsion requirements.

THANK YOU!