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

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Discussion Overview

The discussion revolves around a proposed modification to jet engine design aimed at increasing efficiency by replacing the turbine with an external fan. Participants explore the implications of this idea, including its feasibility during takeoff and operation in steady flight conditions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant proposes a design where the turbine is replaced by a larger coaxial fan around the compressor, suggesting this could enhance efficiency by eliminating velocity losses associated with the turbine.
  • Another participant questions the practicality of this design, noting that the engine would require forward motion to operate effectively, raising concerns about takeoff capabilities.
  • A subsequent reply acknowledges the need for a complementary booster engine to initiate operation, especially when stationary, indicating that additional power sources may be necessary.
  • Some participants mention existing jet engine types, such as ramjets and SCRAMjets, which rely on forward motion and are typically integrated with conventional engines to achieve the required speed for operation.
  • Another participant reflects on the SR-71 Blackbird as an example of a hybrid engine that adjusts its operation based on flying conditions, suggesting that the proposed design might face significant drawbacks despite potential benefits.
  • One participant expresses interest in creating a miniature jet engine prototype, indicating a desire to experiment with the concept practically.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of the proposed jet engine modification, particularly regarding its operation during takeoff and the necessity of additional power sources. The discussion remains unresolved with multiple competing perspectives on the practicality of the idea.

Contextual Notes

Participants highlight limitations related to the need for forward motion in certain jet engine types and the potential challenges of implementing the proposed design in real-world scenarios. The discussion includes assumptions about engine operation that remain unexamined.

Who May Find This Useful

Individuals interested in jet engine design, aerospace engineering, and experimental propulsion systems may find this discussion relevant.

Clausius2
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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 nozzle, and neglecting the mass flow of fuel, the integral momentum equation yields:

[tex]F=\frac{dm_a}{dt}(U_2-U_1)[/tex]

is the force applied to the engine structure.

2=flow conditions behind of the engine
1=flow conditions in front of the engine.

Watching the Turbomachinery equations, one can guess that a compressor accelerates the absolute flow: the blades acts on compressing the relative flow, increasing the static and total pressure, decreasing relative velocity to the blade, and increasing the absolute velocity respect to the stator. We can say that behind the compressor the velocity is the largest (but it will have a lot of swirl). By contrast, the turbine deccelerates the flow, but it provides the energy of rotation to the compressor. So that, we are paying a lost of velocity to gain efficiency on the consumption of energy.

The question is: remove only the turbine and put around the compressor fairing a larger fan coaxially (I mean, like the turbofan engines). In flight conditions, the external fan will provide energy to the compressor. Additionally, the combustion chamber will provide with more enthalpy to the flow. So that we have a maximum [tex]U_2[/tex], without losts of velocity in the turbine.

What do you think?.
 
Last edited:
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Clausius2 said:
What do you think?.
How do you takeoff if the engine requires you to be moving to power itself?
 
russ_watters said:
How do you takeoff if the engine requires you to be moving to power itself?

Good reply russ, but now the air turbine engine needs a complementary booster engine, don't it?. When the plane is stopped, no air flows inside the engine, so theorically no power is supplied by the turbine to the compressor. But in fact it takes off. I don't know very much about jet engine mechanics, but some complementary booster system is neccesary in all jet engines, also in my "dreamt" engine.
 
An extra source of power is required to start a jet engine, but once it is turning it can suck in air through the front, into the compressor and out through the turbine which keeps the engine running (even when stationary). If the turbine was effectively external, that is not in the accelerated airflow, then it could not sustain itself on the ground without quite significant forward movement
 
There are jet engines that cannot function without forward motion (ramjets and SCRAMjets), and these work by being built into other, more conventional engines. The conventional jet engine pushes the vehicle up to the required speed, and then switches over to a different operating mode.
 
i would like to ask the question, do you think it's possible for someone to make a model- working jet engine rocket? id put in my idea but i don't know how to put in pix

Adam
 
I was not intending to init a discussion about engine boosting. Take it as in steady and cruise flight.
 
LURCH said:
There are jet engines that cannot function without forward motion (ramjets and SCRAMjets), and these work by being built into other, more conventional engines. The conventional jet engine pushes the vehicle up to the required speed, and then switches over to a different operating mode.
True, Thr SR-71 Blackbird is a good example of this.
 
Arsonade said:
i would like to ask the question, do you think it's possible for someone to make a model- working jet engine rocket? id put in my idea but i don't know how to put in pix

Adam
A few years back, there was an article in RC modeler about a guy who built a working turbo-jet engine for an RC plane. So yes, it is possible (though not easy).
True, Thr SR-71 Blackbird is a good example of this.
The SR-71 engine is actually a turbo-ramjet hybrid that works just fine at low speed. The main thing that differentiated it from an ordinary turbojet is an inlet cone that moved to focus the shock-wave on the inside of the inlet. It didn't so much "switch modes" as continually adjust for its current flying conditions.
I was not intending to init a discussion about engine boosting. Take it as in steady and cruise flight.
It would probably work, but I think the drawbacks are too big.
 
  • #10
my idea was more trying to actually make a miniture jet engine prototype into an actual rocket, i think I've figured it out and I am going to try it

Adam
 

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