## Valveless front end for a Dynajet

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Mike Everman
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### Valveless front end for a Dynajet

Thought I'd post this somewhere where it was more appropriate. I'd really love it if I had a D-jet to try this on!

To design a valveless intake for a Dynajet:
First, I would determine the current acoustic length of the intake, namely 2.84" (it's physical length is 2.2", the 25 deg angle and inlet acoustic correction of .3d is considered).
Then some for proper tuning, length must be added to the valveless intake because the DJ intake is cold all the time, and our valveless intake(s) will be cold half the time, for some new higher average temperature.

Let's say for grins that this average temp is 650c.
Sound speed at 5c is approx. 334m/sec (an estimate of the DJ intake average temp)
Sound speed at 650c is approx. 608m/sec

So, yeah, (608/334) is a factor of 1.82 times the original acoustic length.
Multiplied by 2.84(dj current intake acoustic length)=5.17" for the valveless equivalent intake length.

If my average temp estimate is off +/-50c, then the (acoustic) length is bounded by 5.03 and 5.31, so not super sensitive to our temperature guess.
All we need now is the intake dia, which should be about 20% of the cc area, or 1.1" dia, which nicely makes for a confinement ratio of .45, and a reasonable aspect ratio for a single intake of 4.7.

Ultimately, then, is it correct that the physical length of a valveless equivalent is twice the original?

5.17 was our valveless intake acoustic length. the dia is 1.1, so the physical length is approx. 5.17-(.3*1.1dia)=4.84
The original physical length of the DJ is 2.2, so the ratio is 2.2!
Considering the acoustic lengths involved, the ratio is 1.82.

That was fun, and yes, probably a bit sloppy!
Mike
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### Re: Valveless front end for a Dynajet

Well that 4.84"x1.1" dia checks out on my acoustic models!
Larry or Mark, want to try a valveless intake for your DynaJet or Bailey?
It's fun enough that I might make up a djet tube, but that's a few projects away...
Mike
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### Re: Valveless front end for a Dynajet

Hi Mike,

I can't wait to jump in the pulse jet adventure. Unfortunately I have problems with the time-space dimensions and \$ dimensions so I have to keep postponing the jump.

The plan that is waiting contains mainly having fun and making noise, but also includes studying the theory. Also I have this idea further on to make comparisions between valved and valveless based upon the same PJ's, meaning, building a modular PJ that can be set up valved or valveless.
Main reason is that in the end I would like to build a valved PJ with airlock's, no valves, like Bruno (dobar dan) discribes in his essay.

Of course (off course ) I will have to start with building the simple ones to get into the matter, I realize.
But since this topic might, by then, have dissappeared deeply under more and more new topics, i'd better ask you right now since you describe exactly what I would eventually like to build:
What are the other dimensions of the Dynajet you are talking about? Is this the Dynajet from the free plans? Or is is a DJ from Eric Becks calculator?

Thank's
Fedde (from that toilet producing country )

By the way, Eric, I found your calculator on a dvd (with free piston jet plans) that i purchased on Ebay, not sold by you.
Your scepticism is fuel for my brain.

ace_fedde
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### Re: Valveless front end for a Dynajet

Mike,
I was mistaken, the Dynajet isn't in the freeplans. Were you thinking about the Dynajet in the attachment?
Fedde
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milisavljevic
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### Re: Valveless front end for a Dynajet

Hola Mike!

This looks like a cool thread to be on right now - a valveless front end for the DynaJet. Woot!
Mike Everman wrote:I would determine the current acoustic length of the intake.
Say it ain't so, but did you forget to add on the end correction (only one) for the valve ports?
Mike Everman wrote:Let's say for grins that this average temp is 650c.
Fascinating choice, as 650 C (923 K) is over 20% higher than the maximum possible acoustic
temperature in any valveless pulsejet, with the induction pipe always operating much cooler.

I would speculate it is much lower, as the acoustic temperature in the DynaJet intake is less
than ambient. If I had to guess --and this is a guess-- I would put the temperature at ~300 C.*

A rough tolerance on my guess: 300 C (+15/-10).
Mike Everman wrote:All we need now is the intake dia, which should be about 20% of the cc area.
If I may, where is this coming from? The presumed "open area" of the valves on the DynaJet?

I would be interested to see how your intake length changes, if you should ever recalculate it.

Cheers,
M.

*The 300 C temperature refers to the proposed valveless intake, not the existing valved one.
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### Re: Valveless front end for a Dynajet

Well I did say it was sloppy!
Mike
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milisavljevic
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### Re: Valveless front end for a Dynajet

Maybe I can give it a go, then?
Mike Everman wrote:Well I did say it was sloppy!
Mmm-mmm-good: sloppy joes!

Cheers,
M.
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### Re: Valveless front end for a Dynajet

Since this is such a fun place to be, please do!
Mike
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milisavljevic
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### Re: Valveless front end for a Dynajet

Only if you bring the sloppy joes! It's raining Chinese dishes 365 days a year up here...

Bon appetit!
M.
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