2004-02-14 - Pulsejet History Well and Truly Made

[Bruno Ogorelec]

Ville, I have been told that those dimensions are not correct. I don't know anything about it myself. Maybe the wrong dimensions have been the reason for the traditionally poor performance.

[Mike Everman]

Ha, you're dreaming. I already have 15 engines and 15 propane tanks!!!

Said Goliath to David! I'm pretty sure that's exactly what he said.

[Bruno Ogorelec]

Milisavljevic,

Do you have plans to publish your mathematical model in a journal somewhere? Do you have plans to use it commercially?

I would like to access it, if it becomes public property. Covering of attendant costs goes without saying.

Alternatively, if the model will remain proprietary, I would be willing to pay for the service of calculation of parameters for a design or two of my own. Do you care to make a quote?

I am not talking of anything urgent -- your own pace will probably be OK if it isn't truly glacial. (Though, the recent data indicate that even the glacial pace has accelerated a lot of late. Maybe it's all those new pulsejets generating a lot of heat....)

[Mark]

Ville and all,
I had forgetton how long the Chinese was in proportion to its width. Looks like the tail end is 2 inches wide on the one Ville just posted but look at the length, 32.625 inches long. For comparisons, we should try to figure the volume it is handling as compared to a Dynajet or something of known values.
It might be almost like comparing 2 pulsejets linked end to end. I don't know, I just know there are gains and trade-offs lurking about.
Mark

[Mark]

I was looking at my little Tigerjet made in Japan. It has an exhaust tube diameter of .866 of an inch. The combustion chamber is 1.732 wide. If you put 2 Tigers end to end, I bet that would approximate the volume of the Chinese pulsejet diagram Ville posted. Anyway, two Tigers would produce 4.5 pounds of static thrust, 2.25 pounds each of course. The Tigerjet is 18.875 inches of combustion length. The whole jet weighs 5.25 oz the schematic says.
If you add on the length of the little side tube of the Chinese, it also would be about the same length as 2 Tigers. I am listing these figures so I can get some idea of how the Chinese compares to typical pulsejets and how it differs. If any of you have any more hard information or ideas...
Mark

[Mark]

I am curious who has a chinese pulsejet and what did they measure for thrust and fuel consumption? Who is the source??? It says 3.3 lbf of thrust, could someone explain that for a simpleton like me.
Mark

c'on guys!
I thought you had a better memory!
first of all, I measured around 1.5 kg of thurst.

I could never measure the fuel compsumtion.
and wont be able to do it till I get my vac cleaner repaired.
Pablo

Pablo,
Was that a total thrust, (1.5 kg), or a thrust per square inch of tailpipe area or mean, (average) cross-sectional area thrust of the whole duct? Was your chinese 2 inches in diameter at the tail pipe?
Thanks,
Mark

[pablo]

total.
basically, it was 2", but it wasnt internal, since I just did 2" * 3.1416
I measured it once welded, and I got 2" external, and since I used 0.5mm black iron, its dia is 1 mm less.

Pablo

[Ray(in England)]

Bruno,
I'm asking you this because Milisavljevic is probably absent now.
So, are the implications of his new formulae as revolutionary as they appear?.

That is to say,will we be able to just bang in a thrust needed, and all dimensions will come out the other end,guarenteed to pulse perfectly?.

How do u think this can work for designs as different
as the Lockwood (U-bend,as I think of it), and the Chinese shown on the recently posted image here.
I know he said he will be soon testing the formulae on a larger scale chinese p.j.,so we don't yet know if it can be scaled up to work at any reasonable (max.ca.2000 N.) thrust needed.

Do u think a single Lockwood or chinese can give enough thrust for a 2000kg. total mass aeroplane?.
I assume it would need about four practically sized such p.js.

Thanks ,Ray.

[Bruno Ogorelec]

are the implications of his new formulae as revolutionary as they appear?. That is to say, will we be able to just bang in a thrust needed, and all dimensions will come out the other end, guarenteed to pulse perfectly?

Well, M. has had his set of equations for some time now and tinkered with it and perfected it. The short answer to your question is, yes, that is indeed what you can do with them. Within reason. Yes, it is revolutionary, as previously such a thing was not possible. By the way, his equations also show the power of acoustics in the pulsejet. If acoustical laws were incidental to the functioning, rather than central, the equations would not work.

we don't yet know if it can be scaled up to work at any reasonable (max.ca.2000 N.) thrust needed.

No, I think we don’t know. As I commented elsewhere, with large volumes you may start running into combustion stability problems. With turbojets, this has long been a problem and the designers went for a series of small combustors rather than a single big one. The same may happen here. We’ll see.

Do u think a single Lockwood or chinese can give enough thrust for a 2000kg. total mass aeroplane?.I assume it would need about four practically sized such p.js.

On paper, yes, but in practice a greater number of small engines may be better. For a small single-seater, maybe two engines of 100 lbs thrust each?

[Ray(in England)]

Thanks for that rapid, and informative reply,Bruno.
I recall reading(altho. my memory may be wrong) that an aeroplane needs at least 10% of its mass in Newtons in thrust in Newtons to take-off.
Can that be correct?.
So a 2000kg. 'plane(ca.20000N.) needs at least 2000 N. thrust.
Which is ca.440lbsf.?.
Ray.

[Mark]

total.
basically, it was 2", but it wasnt internal, since I just did 2" * 3.1416
I measured it once welded, and I got 2" external, and since I used 0.5mm black iron, its dia is 1 mm less.

Pablo

Pablo, what is 2" * 3.1416? The area of a circle is pi times the radius squared. Just confirm what the total thrust was for your jet, not per square inch or anything, just the total thrust so I can be sure of that number.
Wouldn't it be interesting if someone could make a hilariously long chain of Chinese pulsejets somehow, with only one exhaust tail pipe and several side ports directed rearward up and down the length, the whole enchalada resonatating and firing like some laser beam of pulsating energy. I would name it the Grasshopper, because that's how they breathe, with little holes in a straight line on both sides of their bodies, and not through their mouths.
Thanks,
Mark

[pablo]

sorry, that is what I did to calculate the width of the piece of iron to make the cilinder,

so its diameter is 49.8 mm (1 " - 1 mm)
for 1.5 kg
it is not a big difference in that part, but in the intake, wich is less than 1", It becomes a big difference, I wonder how it would have worked if I had cut the iron to get the measures right.
Pablo

[mk]

Pablo,
by the way, what kind of fuel do you use? And have you added a needle scew to the atomizer pipe outflow ending to adjust fuel flow, if you are using liquid fuel?

Plays the exact intake length a big role or can I lengthen or shorten it within 1/2" or 1"?

[pablo]

nope, since I use a propane cilinder. I wanted to try liquid fuel, but my vac cleaner is dead now, so I cant start it.
Pablo

[mk]

Do you use a vaporizer or do you just let it flow 90° to the airflow? I tried starting my Chinese type pj with propane and a vaporizer without success. But the temperatures where pretty low those days...