Wanted: plans for a 10-20Lb valveless PJ

Moderator: Mike Everman

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Sat Nov 22, 2014 7:35 pm

I am looking for plans for a valveless pulsejet capable of 10-20 pounds of thrust. I would have use some of the other plans available on this site, but it needs to have only one intake, which must be forwards facing, no bends, no thrust augmenter. Should be as compact as possible and built for speed.

Some of you might be wondering why I would want an engine that is one of the least efficient at producing static thrust, it's simple: I am going to mod the shit out of it, and the experimental mods I plan on doing require a forwards facing intake, no valves, no augmenter, and are much easier to apply to a straight engine. Once I get the results from the experiments I will post them, seeing as getting any information about the mods I plan to try is like trying to find a specific needle in a pile of decoy needles when the needle may not even exist yet.


I would use PyroJoe's recipe for beginners, but I tried that design, the test engine doesn't even need to be clamped down because it doesn't have enough thrust to push itself off of it's test stand. It is made of .019" steel, a 4" CC, and a single GRIMjector, which considering the amount of flame that the intake would spit out when I turned the tank upside down was delivering all the fuel the engine can take. Even with the cone transition to the exhaust pipe and a flared intake it still had almost no thrust.

metiz
Posts: 1515
Joined: Fri Apr 21, 2006 6:34 pm
Antipspambot question: 125
Location: Netherlands

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by metiz » Sat Nov 22, 2014 11:59 pm

You know you can just slap the intake of an existing engine on the front right?
Quantify the world.

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Mon Nov 24, 2014 11:30 pm

metiz wrote:You know you can just slap the intake of an existing engine on the front right?
No, the reverse facing intake designs either don't even try to use aerodynamic valving* (like the lockwood), or have a design that pretty much demands that the intake is placed where it is (like the FWE).

*Aerodynamic valving basically uses engine geometry to reduce the amount of blow-back from the intake without choking the engine. Lack of aerodynamic valving means there is a larger than normal thrust penalty for facing the intake forwards, the Lockwood supposibly gets ~40% of it's thrust from the intake, which would represent an 80% loss in thrust because aerodynamic valving is completely ignored, or even discouraged in it's design.

metiz
Posts: 1515
Joined: Fri Apr 21, 2006 6:34 pm
Antipspambot question: 125
Location: Netherlands

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by metiz » Tue Nov 25, 2014 10:29 am

lovot wrote:Some of you might be wondering why I would want an engine that is one of the least efficient at producing static thrust
Using your own words, apparently, thrust and efficiency don't matter, hence the suggestion.
Quantify the world.

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Tue Nov 25, 2014 11:55 pm

metiz wrote:
lovot wrote:Some of you might be wondering why I would want an engine that is one of the least efficient at producing static thrust
Using your own words, apparently, thrust and efficiency don't matter, hence the suggestion.
There is a difference between "I know the design limitations, and am prepared to accept them" and "I don't care if I take close to the maximum possible thrust and efficiency penalties"

sockmonkey
Posts: 58
Joined: Tue Mar 10, 2009 2:29 am

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by sockmonkey » Wed Nov 26, 2014 4:59 am

At least it should provide some useful data.

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Wed Nov 26, 2014 11:58 pm

I thought that there had to be someone here who knows how to make good valveless straight engines. Seems I was mistaken. I guess it's back to designing my own engines, which hasn't been successful in the past. I guess if I experiment enough I might make something functional.

tufty
Posts: 843
Joined: Wed Dec 24, 2003 12:12 pm
Antipspambot question: 0
Location: France
Contact:

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by tufty » Thu Nov 27, 2014 5:24 pm

You want a straight valveless? Escopette / Escopeta

viewtopic.php?f=3&t=627

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Fri Nov 28, 2014 3:28 am

tufty wrote:You want a straight valveless? Escopette / Escopeta

viewtopic.php?f=3&t=627
Thanks, I actually tried looking for some Escopette stuff, and couldn't find much about it except that it was a successful engine, not much information about thrust, efficiency or maximum operating speed. The Escoppette seems to be around 8' long, which is pretty large. Any idea how I would go about scaling it down to something more manageable, like 4' minus the intake horn?

tufty
Posts: 843
Joined: Wed Dec 24, 2003 12:12 pm
Antipspambot question: 0
Location: France
Contact:

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by tufty » Fri Nov 28, 2014 5:24 pm

lovot wrote:
tufty wrote:You want a straight valveless? Escopette / Escopeta

viewtopic.php?f=3&t=627
Thanks, I actually tried looking for some Escopette stuff, and couldn't find much about it except that it was a successful engine, not much information about thrust, efficiency or maximum operating speed. The Escoppette seems to be around 8' long, which is pretty large. Any idea how I would go about scaling it down to something more manageable, like 4' minus the intake horn?
It's probably the best documented engine out there. Look harder.

FWIW, 10-15 Kg thrust, 1.6-1.8Kg/KgF/Hr, operates up to about Mach 0.7

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Sat Nov 29, 2014 12:48 am

tufty wrote:
lovot wrote:
tufty wrote:You want a straight valveless? Escopette / Escopeta

viewtopic.php?f=3&t=627
Thanks, I actually tried looking for some Escopette stuff, and couldn't find much about it except that it was a successful engine, not much information about thrust, efficiency or maximum operating speed. The Escoppette seems to be around 8' long, which is pretty large. Any idea how I would go about scaling it down to something more manageable, like 4' minus the intake horn?
It's probably the best documented engine out there. Look harder.

FWIW, 10-15 Kg thrust, 1.6-1.8Kg/KgF/Hr, operates up to about Mach 0.7
Thanks, any idea how to scale it down to around half it's current length? if not I will try to scale it by halving all of the lengths and cross sectional areas. Not sure if it would even run with that scaling method.

tufty
Posts: 843
Joined: Wed Dec 24, 2003 12:12 pm
Antipspambot question: 0
Location: France
Contact:

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by tufty » Sat Nov 29, 2014 9:52 pm

scaling, especially downwards, is generally a bad idea.

here's another set of escopette dimensions

Image

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Sun Nov 30, 2014 7:11 am

tufty wrote:scaling, especially downwards, is generally a bad idea.

here's another set of escopette dimensions

Image
I know scaling is a bad idea, but I don't have much choice. 4' is the upper limit for a test engine, otherwise the engine uses so much of my limited metal supplies and fuel that problems arise. I am not made of money. One thing potentially improving my chances of successfully scaling the engine and it still work is I'm scaling the cross sectional area of each piece instead of scaling the diameter linearly, which should result in the same cross sectional area to length ratio as the original, and hopefully work the same except with double the frequency. Again, I have no idea if this will work, but the lack of small straight engines that do not contain mechanical valves, but still have passable efficiency drives me to do things that probably won't work, and hope I get lucky. I'm sure such engines exist, but finding them is somewhat difficult, which is why I wanted to draw upon the knowledge the members of this forum posses to find such an engine. That didn't go as planned, so now I have a good engine design that's way too big, and my options are either scale it, and pray it works, or use my n00b powers to somehow invent a new PJ type that meets my requirements. My n00b powers have managed to make one Ramjet*, and two bricks when I was trying for a PJ. The odds aren't in favor of my n00b powers, so scaling it is.

*The ramjet requires a lot of ram air to work (a fairly powerful air compressor (it's 1.5 or 2.5HP, or something, and unlike shop vacs, air compressors actually have accurate HP measurements) going at full blast right before the compressor cone), but once it has enough it seems to be pretty powerful for it's size, or at least make an impressive amount of noise for something that's less than 2 feet long. That was my very first attempt at making a pulsejet. IDK, maybe i'll see what I can do with it later when I have have more resources.

tufty
Posts: 843
Joined: Wed Dec 24, 2003 12:12 pm
Antipspambot question: 0
Location: France
Contact:

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by tufty » Sun Nov 30, 2014 8:03 am

If you scale the escopette, it becomes something else, and any ideas of the original being easy to start, running consistently, producing x thrust, running at y Hz, etc, go straight out of the window.

Frequency is determined by the length of the engine and the speed of sound at running temperature. Combine that with the combustion speed of the fuel mix, and you have a major impact on how and when combustion occurs. The higher the frequency, the less time your fuel has to burn, making it harder to tie the two together. Likewise, as frequency goes up, you have less time to *mix* fuel and air, making injector design and placement more critical.

That's just the impact of modifying *one* variable. After that, you have relative lengths of inlet to combustion chamber to exhaust, form of combustion chamber and exhaust, how the inlet enters the chamber...

There's a wealth of information on this site regarding pulse-jet design, some of which might even be close to accurate. I'd be looking at the (stickied) PyroJoe's recipes thread, and searching the site for the "Hinote Criteria".

In theory, it should be possible to take a design from "muzzle" to "breech" loading and vice versa (Mike "chinesed" some of his kazoo engines, IIRC, so that's another thing to search for); it should be possible to go from the Chinese design (Eric's version is probably / currently considered to be the best) and move the intake to the front, but I'm not sure how the lengths work on that. A "trombone" intake might be worthwhile...

Pyro also did a linear FWE, then folded it radically. So they work with a muzzle loader configuration, too.

I'd probably use Eric Beck's fabulous Pulsejet Engine Calculator, double check against the Hinote Criteria and PyroJoe's stuff, and then say "the hell with it, TLAR".

lovot
Posts: 19
Joined: Wed May 07, 2014 6:29 pm
Antipspambot question: 125

Re: Wanted: plans for a 10-20Lb valveless PJ

Post by lovot » Sun Nov 30, 2014 8:01 pm

tufty wrote:If you scale the escopette, it becomes something else, and any ideas of the original being easy to start, running consistently, producing x thrust, running at y Hz, etc, go straight out of the window.

Frequency is determined by the length of the engine and the speed of sound at running temperature. Combine that with the combustion speed of the fuel mix, and you have a major impact on how and when combustion occurs. The higher the frequency, the less time your fuel has to burn, making it harder to tie the two together. Likewise, as frequency goes up, you have less time to *mix* fuel and air, making injector design and placement more critical.

That's just the impact of modifying *one* variable. After that, you have relative lengths of inlet to combustion chamber to exhaust, form of combustion chamber and exhaust, how the inlet enters the chamber...

There's a wealth of information on this site regarding pulse-jet design, some of which might even be close to accurate. I'd be looking at the (stickied) PyroJoe's recipes thread, and searching the site for the "Hinote Criteria".

In theory, it should be possible to take a design from "muzzle" to "breech" loading and vice versa (Mike "chinesed" some of his kazoo engines, IIRC, so that's another thing to search for); it should be possible to go from the Chinese design (Eric's version is probably / currently considered to be the best) and move the intake to the front, but I'm not sure how the lengths work on that. A "trombone" intake might be worthwhile...

Pyro also did a linear FWE, then folded it radically. So they work with a muzzle loader configuration, too.

I'd probably use Eric Beck's fabulous Pulsejet Engine Calculator, double check against the Hinote Criteria and PyroJoe's stuff, and then say "the hell with it, TLAR".
A low frequency engine with good mixing would be great, and going from PyroJoe's thread, tail expansion significantly increases the operating frequency, which could be useful on very large engines that operate at a very low frequency, but might be harmful to a small engine when using fuels that have trouble burning quickly and need more mixing time. I can see why down-scaling the Escopette in particular would be a problem because it uses the most tail expansion I have seen thus far.

Any links to converted engines would be great, like I said the only design stuff I have found that actually works is from PyroJoe, and while the advice is sound, and the resulting engine works, it has some serious efficiency issues. I found the calculator you directed me to a while back, but it only has valved designs, which don't use quite the same design as valveless PJs, and most likely aren't compatible. I tried searching for Hinote Criteria on the forums, but while it was mentioned repeatedly, it was never really explained. I saw a thread about converting the FWE to a straight piped engine, but the OP hadn't figured it out at the time: viewtopic.php?f=3&t=5546, the thread was abandoned before the OP tried any of the suggestions, so I won't ever know if it ever ran.

Post Reply