What is Jet engine: Definition and 74 Discussions

A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion airbreathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.
Airbreathing jet engines typically feature a rotating air compressor powered by a turbine, with the leftover power providing thrust through the propelling nozzle—this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines. They give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high speed applications (ramjets and scramjets) use the ram effect of the vehicle's speed instead of a mechanical compressor.
The thrust of a typical jetliner engine went from 5,000 lbf (22,000 N) (de Havilland Ghost turbojet) in the 1950s to 115,000 lbf (510,000 N) (General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in the late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where previously a similar journey would have required multiple fuel stops.

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  1. A

    Pulse Jet engine - A new design concept

    I`ve had a new idea in designing a pulse jet by adding a valve in it... According to my intuition and logically this increases the output many folds and I`ve given sufficient reasons for suggesting it. I have a powerpoint of my idea that I have made and I request any of you to please go through...
  2. V

    Jet Engine Mass Flow Rate calculation

    hi how to find air mass flow rate in jet engine? we are using thrust/Isp equation to find the mass flow rate for rocket equation. is that any formula available for finding the mass flow rate in jet engine
  3. V

    Jet Engine Compressed air Pressure for various altitude and velocity

    HI In Jet Engine, i want to know that the compressed air prssure changes before it enters into the combustion chamber from the compressor in various altitude and velocity or it is consatnt for altitude and velocity?
  4. C

    How Is Thrust Calculated for a Jet Engine in a Lab Test?

    Homework Statement A jet engine is being tested in the laboratory and it is found to consume 20 kg of air per second while using 0.2 kg of fuel per second. Given that the exit velocity of the gases is 500 m s-1, calculate the thrust generated by the engine. Homework Equations F = M(V-U)...
  5. G

    Determining the Dimensions of a Pulse Jet Engine: A Scientific Approach

    If you were to design a pulse jet engine where would you start? How do you determine the diameter and length of the tail pipe? How do you determine the diameter and length of the combustion chamber? How do you determine the area of the air intake valve system? How do you determine...
  6. G

    How Can I Calculate Pulse Jet Engine Dimensions Using Air as Oxidizer?

    Does anyone know any Forumulas or how to calculate the dimensions of a pulse jet engine? I have already built several PULSE JET engines that run by scaling up an existing hobby engine to a larger size. Problem is the scaled up models run but maybe they could run better. I can not find any...
  7. P

    Jet Engine Inlet Distortion

    (This is a homework/lab assignment but thought it better suits in this category) Hi, This is a scaled model and I am given the pressure tap locations on each rakes. Also given is the pressure data. Inlet distortion formula is given by: Pdist = (Pmax - Pmin)/Pavg Question is to find...
  8. P

    Jet Engine Thrust in Atmosphere vs Space

    A rocket flying in the atmosphere and flying in the outer space. In which conditions does it have stronger thrust? Provided every parameter is the same, even the air drag is considered negligible (in fact it's big).
  9. A

    How Does Thermodynamics Apply to Jet Engine Functionality?

    Homework Statement http://img183.imageshack.us/img183/3628/jetlf0.jpg http://img393.imageshack.us/img393/1759/jet2iu4.jpg Homework Equations The Attempt at a Solution H = U + pV is the enthalpy, and hence the enthalpy per unit mass is h = U/m + pV/m which I have...
  10. M

    Jet Engine: Turbine Blades and Temperature

    Hey! I am trying to find some figures on the environmental conditions a turbine blade in a Jet Engine would have to withstand, and the materials that are necessary to prevent the blade from failing. I have taken the example of the 'Trent Engine' or so I think it is called. I have read that...
  11. B

    Jet Engines and the Forces They Create - Confirmed?

    last year i did a jet engine workshop n one of the instructor there told us that both the engines on an aircraft(ofcourse an aircraft with an engine on each wing or maybe more on each) are run in same direction(i mean same sense of rotation) n this induces a transeverse force of the aircraft...
  12. P

    Jet engine thermodynamic non sequitur.

    Hi all, This has been bugging me all day, so I thought I'd seek the help and advice of the internet. When a plane is stationary, you’d have to say that its jet engines are doing no useful work. The engines apply a static force on the airframe and could be said to be running at zero...
  13. P

    Jet Engine Doubt: How Does Temp & Pressure Affect Efficiency?

    A Jet Engine doubt... Hi folks... My aerospace propulsion professor taught me that, in the combustion chamber of a jet engine, during combustion, the pressure instead of increasing, decreases. I have 2 questions. 1) Is it true? 2) If yes, how? How and in what way does temperature, and...
  14. S

    Temperature of the back of a turbine jet engine (or something like that)

    can anybody please tell me the temperature (degrees Celsius please.) there is at the back of a normal turbine jet engine (or something like that:-p )?? i couldn't find it on wikipedia or something like that:frown: so i ask it here:approve:
  15. B

    Calculate Jet Engine Thrust for 800 kg Jet Takeoff with 4 m/s^-2 Acceleration

    Homework Statement Calculate the engine thrust required to produce an acceleration of 4 m/s^-2 in a jet of mass 800 kg as it takes off along the runway. The air resistance is 500 N Appreciate if anyone can check if I have used the correct equation, and my answer. Homework Equations F - R...
  16. J

    Understanding Airflow and Pressure Changes in Jet Engine Design

    Hello, I'm Arman, new user here. I'm a jet-engine designer and I'm really interested in building and running different types of jet engines. I have quetion now: Some amount of air enters a cone shaped pipe with a minimum diameter of 6 cm and a maximum diameter of 10 cm, and a length of 7 cm...
  17. K

    Can a Jet Engine Work Without Air?

    OK I have question about the way jet engine works. I am only 16 and haven't got into any of this stuff in hs yet. my buddy and I were having a disscusion about the way a jet and rockets work and got stump by something. I looked up online how they both work and heard of people refferring to a...
  18. S

    Building a Small Jet Engine: Experiences & Parts

    Has anyone here ever built a small Jet engine? Just generally interested in how you did it and from what parts thanks
  19. Integral

    What to do with a used helicopter jet engine?

    For those with a strong death wish only.
  20. A

    Jet Engine Intakes: Why the Squashed, Flat Design?

    I half remember that jet engine intakes were circular a few years ago. Now they have a squashed appearance with the bottom part quite flat. This isn't new as the first German jet at the end of World War II had the same shape but it seems relatively new on airline jet engines. So, why are...
  21. S

    Hot Air in Jet Engines: Fuel Burn and CO2 Formation

    When fuel is burnt in the jet engine, what is the major component of the hot gases thrown out of the back - the CO2 formed (I know CO2 is not the only component but it is the major one) from the fuel or the air entering the jet as a whole? In other words, does the heat of the burning fuel...
  22. P

    Calculating Jet Engine Output of an Airplane

    The jet engine of an airplane takes in 100 kg of air per second, which is burned with 4.2 kg of fuel per second. The burned gases leave the plane at a speed of 550 m/s (relative to the plane). If the plane is traveling 270 m/s. (a) Determine the thrust due to ejected fuel. This...
  23. Clausius2

    Revolutionizing Jet Engine Design: A New Idea to Increase Efficiency?

    What do you think of this?. I was a brainwave when I sat on the toilet :smile: . A typical jet engine compresses the air when it comes into the compressor, burns it with fuel, and expands it in the turbine. Approximating there is no difference of static pressure between the entrance and the...
  24. N

    Noise reduction in a jet engine

    I am in the process of writing a report on the Physics of Jet engines and I have come across a problem I cannot comprehend. In the exhaust of many jet engines they allow the atmospheric air to mix with the air from the engine to reduce exhaust noise. From what I understand this allows the...
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