Valveless front end for a Dynajet

Moderator: Mike Everman

Post Reply
Mike Everman
Posts: 4930
Joined: Fri Oct 31, 2003 7:25 am
Antipspambot question: 0
Location: santa barbara, CA
Contact:

Valveless front end for a Dynajet

Post by Mike Everman » Mon Dec 15, 2008 9:05 pm

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
__________________________
Follow my technical science blog at: http://mikeeverman.com/
Get alerts for the above on twitter at: http://twitter.com/mikeeverman

Mike Everman
Posts: 4930
Joined: Fri Oct 31, 2003 7:25 am
Antipspambot question: 0
Location: santa barbara, CA
Contact:

Re: Valveless front end for a Dynajet

Post by Mike Everman » Mon Dec 15, 2008 11:55 pm

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
__________________________
Follow my technical science blog at: http://mikeeverman.com/
Get alerts for the above on twitter at: http://twitter.com/mikeeverman

ace_fedde
Posts: 421
Joined: Mon Feb 16, 2009 9:26 pm
Antipspambot question: 0
Location: The Netherlands

Re: Valveless front end for a Dynajet

Post by ace_fedde » Sat Feb 21, 2009 8:04 pm

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.
I have been reading various sites, downloading plans etc. and lately I subscribed this forum.

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 :lol: )

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
Posts: 421
Joined: Mon Feb 16, 2009 9:26 pm
Antipspambot question: 0
Location: The Netherlands

Re: Valveless front end for a Dynajet

Post by ace_fedde » Sun Feb 22, 2009 10:32 am

Mike,
I was mistaken, the Dynajet isn't in the freeplans. Were you thinking about the Dynajet in the attachment?
Fedde
Attachments
DYNA_2.GIF
DYNA_1.GIF
Your scepticism is fuel for my brain.

milisavljevic
Posts: 855
Joined: Sat Oct 04, 2003 9:36 am
Antipspambot question: 125

Re: Valveless front end for a Dynajet

Post by milisavljevic » Sun Feb 22, 2009 11:23 am

Hola Mike!

This looks like a cool thread to be on right now - a valveless front end for the DynaJet. Woot! 8)
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.
no safe haven for merchant scum


for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

avast!
Cap'n M.

Mike Everman
Posts: 4930
Joined: Fri Oct 31, 2003 7:25 am
Antipspambot question: 0
Location: santa barbara, CA
Contact:

Re: Valveless front end for a Dynajet

Post by Mike Everman » Sun Feb 22, 2009 8:10 pm

Well I did say it was sloppy!
Mike
__________________________
Follow my technical science blog at: http://mikeeverman.com/
Get alerts for the above on twitter at: http://twitter.com/mikeeverman

milisavljevic
Posts: 855
Joined: Sat Oct 04, 2003 9:36 am
Antipspambot question: 125

Re: Valveless front end for a Dynajet

Post by milisavljevic » Mon Feb 23, 2009 2:35 am

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

Cheers,
M.
no safe haven for merchant scum


for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

avast!
Cap'n M.

Mike Everman
Posts: 4930
Joined: Fri Oct 31, 2003 7:25 am
Antipspambot question: 0
Location: santa barbara, CA
Contact:

Re: Valveless front end for a Dynajet

Post by Mike Everman » Mon Feb 23, 2009 2:46 am

Since this is such a fun place to be, please do!
Mike
__________________________
Follow my technical science blog at: http://mikeeverman.com/
Get alerts for the above on twitter at: http://twitter.com/mikeeverman

milisavljevic
Posts: 855
Joined: Sat Oct 04, 2003 9:36 am
Antipspambot question: 125

Re: Valveless front end for a Dynajet

Post by milisavljevic » Mon Feb 23, 2009 3:09 am

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

Bon appetit!
M.
no safe haven for merchant scum


for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

avast!
Cap'n M.

Post Reply