Pulse Jet engine - A new design concept

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Discussion Overview

The discussion centers around a new design concept for a pulse jet engine that incorporates a valve system to potentially enhance its efficiency and output. Participants explore the feasibility of this design, share personal experiences with pulse jets, and discuss various technical aspects related to jet engine performance, including airflow, combustion dynamics, and modeling challenges.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • One participant proposes adding a valve to a pulse jet design, suggesting it could significantly increase output.
  • Another participant questions the feasibility of a silent pulse jet, referencing personal experiences with noise levels in similar engines.
  • Concerns are raised about airflow restrictions caused by the proposed valve design, which could impact the engine's performance.
  • A participant suggests using iris shutters as a potential valve mechanism, citing their controllability and minimal aerodynamic impact.
  • Discussion includes the idea that valved pulse jets may be more efficient than valveless designs due to better management of fresh air intake and exhaust pressure.
  • Some participants express interest in conducting computational fluid dynamics (CFD) analysis to validate the proposed design but note challenges in modeling and simulation.
  • There are suggestions to explore multiple mesh simulations to simplify the modeling process for the combustion chamber.

Areas of Agreement / Disagreement

Participants express a range of opinions regarding the proposed valve design's feasibility and effectiveness. While some support the idea and suggest improvements, others raise concerns about potential complications and the need for further analysis. Overall, the discussion remains unresolved with multiple competing views on the design's viability.

Contextual Notes

Participants mention limitations in their understanding of CFD modeling and the complexities involved in simulating the proposed engine design. There are also references to existing technologies and applications of pulse jets, indicating that the discussion is grounded in ongoing research and development.

Who May Find This Useful

This discussion may be of interest to aerospace engineering students, researchers in jet propulsion technologies, and hobbyists exploring advanced engine designs.

  • #31
Phrak said:
The front valve is a ram--so needs additional thought. The shaft should be larger diameter and hollow for air cooling.

Shouldn't be to much worse than a petal valve, and doesn't have to bend, but thickness would need to be a consideration to balance weight and durability. Air cooling sounds interesting... Would help with the weight factor, too, I guess.
 
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  • #32
jarednjames said:
There we go, that's basically what I was going to describe, but I was going to try and explain the 'why' as well - hence waiting for tomorrow.

I'll be looking forward to that.
 
  • #33
Phrak said:
It may need a retention spring somewhere.

jarednjames said:
There we go, that's basically what I was going to describe...

Just a guess, but is this basically what you are referring to?
telepresence said:
The question is, will a sufficiently strong vacuum be able to form before the valves switch to intake position...
 
  • #34
aryanscarlet said:
However I am unclear abt the working.

basically something like this:
 

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  • #35
Very cool. What might happen with an 'S' shaped orifice?
 
  • #36
Got it guys! Sorry, mistook the ball mechanism! Now its clear. Glad people have pitched in ideas. Will keep posted on my work too.
 
  • #37
I made a small change to telepresence's idea. In this valving, the flow right after after combustion is straight thru the valve instead of a sudden reduction in area which causes fluid dynamic losses. Also with the smaller valve, when closed, due to smaller area of cross section of the ball, the pressure on the valve and also the hoops stress on the walls of the combustion chamber will be greater. Also when the valve is closed and combustion takes place, the convergent section will also be a part of the chamber and the hoops stress would be pronounced on the walls and the sharp area changes will produce turbulence during combustion and problems in flame stabilization.

The inlet could also be of the size of the second valve or even a normal v- shutter inlet would do.

Any contradictions or improvements guys?
 

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  • #38
it seems like that would reduce the power of the engine if you use the valve as part of the combustion chamber. I was seeing the combustion happening while both valves were closed to boost the pressure and ensure that the fuel burns while still inside the engine and not after it leaves. I could be wrong, though.
Also, remember that these valves are constantly spinning. the snapshot you have in that image would only be the case for an instant, certainly not long enough for the entire combustion and exhaust processes to take place.
 
  • #39
telepresence said:
it seems like that would reduce the power of the engine if you use the valve as part of the combustion chamber. I was seeing the combustion happening while both valves were closed to boost the pressure and ensure that the fuel burns while still inside the engine and not after it leaves. I could be wrong, though.

aryanscarlet's single valve design is along the lines of what I was thinking of. The dual ball valve system is just over complicating things and I don't see any real gain to be had by doing it. Not to mention increasing the chance of backfire / complete detonation.
Also, remember that these valves are constantly spinning. the snapshot you have in that image would only be the case for an instant, certainly not long enough for the entire combustion and exhaust processes to take place.

The 'snapshot' would be the midpoint of combustion - hopefully the point when the exhaust is being expelled to greatest advantage.

It wouldn't have to be there for the whole process, just enough to gain an advantage.
 
  • #40
No you guys have misunderstood me. I did not mean that the combustion will happen with one valve open. That is totally against the entire idea itself. I meant, when the valve is fully open, it must be coincident with the combustion chamber and not like telepresence's first diag. The combustion will happen when both valves are closed only. In the initial idea, the nozzle section that led to the ball valve would cause flame instabilities which can be avoided in the changed diag. Also the opening and closing is up to us to decide based on preliminary tests and optimization can be done. The valve can be left closed for a prolonged time also or reduced time also based on the size, thrust req etc. This can be done by a simple cam.
 
  • #41
aryanscarlet said:
Also when the valve is closed and combustion takes place...

Okay, my bad. Missed that little "and" connection there.
 
  • #42
jarednjames said:
There we go, that's basically what I was going to describe, but I was going to try and explain the 'why' as well - hence waiting for tomorrow.

I really would like to hear this.
 
  • #43
telepresence said:
I really would like to hear this.

Sorry, really busy.

During combustion, there is a force applied to the front "sail". This forces it closed, ensuring all exhaust is directed backwards.

Your biggest problem is that you are assuming the thrust acting on the "pyramid" section + suction created will be enough to force the "sail" to open. Remember, there will be air drawn in through the rear during this time which will act against the rear "pyramid" creating a force that will try to counteract the suction acting on the "sail". The net effect is likely to be that the front "sail" section will remain at least partially, if not fully closed. Efficiency will be lost.

RE Bolded: the force acting on the forward "sail" will be far in excess of the force on the rear "pyramid" so it will easily counteract any effects.

So you need a spring to force the rear "pyramid" valve closed and the forward "sail" valve open. That way, the combustion will act against the forward "sail" to close it and direct all exhaust out of the back. Once complete the spring will force the valve to switch and suction to occur from the front.
 
  • #44
jarednjames said:
Sorry, really busy.

Aren't we all... :smile:

Thanks for your response. I do see the need for a spring there.
 

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