Represented by Eng. ALI F. ALI jet engine Arab academy for science and technology
How does a jet engine work
A jet engine is an engine that accelerates and discharges a fast moving jet of fluid to generate thrust in accordance with Newton 's third law of motion . This broad definition of jet engines includes turbojets , turbofans , rockets and ramjets and water jets , but in common usage, the term generally refers to a gas turbine used to produce a jet of high speed exhaust gases for special propulsive purposes.
The basic components (parts) of a jet (air-breathing) engine are the : inlet, compressor or fan, combustor (burner), a turbine (engine) and an exit nozzle. Some engines may not have all these parts. The figure below shows a jet engine with these components
The inlet is where the air goes into the engine. The inlet slows the air flow into the compressor. The compressor works better when the air flow coming in is slow. The inlet is made differently if the airplane is going to fly faster than the speed of sound
The compressor takes air in and squeezes it. The same thing happens to the air you blow into a balloon. When the air under pressure goes out of the balloon it causes thrust (push). When the air leaves the compressor it is mixed with fuel (gas) and burned. The gases move at high speed, just like coming out of a balloon.
As the air comes into the combustor it is mixed with fuel and burned. The right amount of air and gas must be mixed and burned to get the most thrust. The gases become very, very hot. The engineer must make sure the combustor is made of metals that will not bend or break when there is high heat. The hot gases that come out go to the turbine to increase thrust and to run the compressor .
A turbine is also called an engine. This engine or turbine runs the compressor. The hot gases move very fast out of the combustor through the turbine and out into the air as thrust.
Sometimes an "afterburner" is added after the turbine. The afterburner heats up the gases again to get more thrust. The amount of heat is important. Too much heat can bend or break parts in the turbine.
All the heated gases finally come out the back end of the jet engine through a nozzle. The nozzle is designed a special way to help the hot gases move even faster. This creates more thrust. The nozzle must be made of the kind of metals that won't melt or bend under high heat.
How does a jet engine work
jet engine uses a gas turbine to drive a fan that sucks in air, mixes it with burning fuel, and then blasts the expanded air-gas mixture out the back . Because every action has an equal and opposite reaction, as the air streams backward the engine is forced forward .
There are a large number of different types of jet engines, all of which get propulsion from a high speed exhaust jet.
Disadvantages Advantages Description Type Can be less efficient than a propeller, more vulnerable to debris Can run in shallow water, powerful, less harmful to wildlife Squirts water out the back of a boat Water jet
Heavy, inefficient and underpowered Can run in shallow water, powerful, less harmful to wildlife Most primitive airbreathing jet engine. Essentially a supercharged piston engine with a jet exhaust . thermojet Basic design, misses many improvements in efficiency and power Simplicity of design Generic term for simple turbine engine turbojet
Greater complexity (additional ducting, usually multiple shafts), large diameter engine, need to contain heavy blades. More subject to FOD and ice damage. Top speed is limited due to the potential for shockwaves to damage engine Quieter due to greater mass flow and lower total exhaust speed, more efficient for a useful range of subsonic airspeeds for same reason, cooler exhaust temperature First stage compressor greatly enlarged to provide bypass airflow around engine core turbofan Needs lots of propellant- very low specific impulse - typically 100-450 seconds. Extreme thermal stresses of combustion chamber can make reuse harder. Typically requires carrying oxidiser onboard which increases risks . Very few moving parts, Mach 0 to Mach 25+, efficient at very high speed (> Mach 10.0 or so), thrust/weight ratio over 100, no complex air inlet, high compression ratio, very high speed exhaust, good cost/thrust ratio, works best exoatmospheric which is kinder on vehicle structure at high speed . Carries all propellants onboard, emits jet for propulsion roket
Limited top speed (aeroplanes), somewhat noisy, complex transmission High efficiency at lower subsonic airspeeds(300 knots plus), high shaft power to weight Strictly not a jet at all — a gas turbine engine is used as powerplant to drive (propeller) shaft TURBOPROP Development of propfan engines has been very limited, typically more noisy than turbofans, complexity Higher fuel efficiency, potentially less noisy than turbofans, could lead to higher-speed commercial aircraft, popular in the 1980s during fuel shortages Turboprop engine drives one or more propellers. Similar to a turbofan without the fan cowling . PROPFAN
Noisy, inefficient (low compression ratio), works poorly on a large scale, valves on valved designs wear out quickly Very simple design, commonly used on model aircraft Air is compressed and combusted intermittently instead of continuously. Some designs use valves . PULSJET Extremely noisy, parts subject to extreme mechanical fatigue, hard to start detonation, not practical for current use Maximum theoretical engine efficiency Similar to a pulsejet, but combustion occurs as a detonation instead of a deflagration , may or may not need valves PULS DETONATION ENGINE
Still in development stages, must have a very high initial speed to function (Mach >6), cooling difficulties, very poor thrust/weight ratio (~2), extreme aerodynamic complexity, airframe difficulties, testing difficulties/expense Few mechanical parts, can operate at very high Mach numbers ( Mach 8 to 15) with good efficiencies  Similar to a ramjet without a diffuser; airflow through the entire engine remains supersonic SCRAMJET
Airspeed limited to same range as turbojet engine, carrying oxidizer like LOX can be dangerous Very close to existing designs, operates in very high altitude, wide range of altitude and airspeed A turbojet where an additional oxidizer such as oxygen is added to the airstream to increase max altitude TURBOROKET Exists only at the lab protoyping stage. Examples include RB545 , SABRE , ATREX Easily tested on ground. Very high thrust/weight ratios are possible (~14) together with good fuel efficiency over a wide range of airspeeds, mach 0-5.5+; this combination of efficiencies may permit launching to orbit, single stage , Intake air is chilled to very low temperatures at inlet before passing through a ramjet or turbojet engine PRECOOLEDJET