origonal ???

[paul fellows]

i am fairly new to pulse jets and have been looking for some one to tell me why acoustic resonanses are so important, people kept saying that it was important but were vauge about the how and why. so i went forward basing my thought on kadenacy wich made sence.
thanks to crazycorkey who put me on to this site
http://jetzilla.com/topic_003_01.html
i think mayby acoustics do make sence
any way at any point i have talked about acoustic cancilling before the 17/3/10 is unfortunatly nonsence
sorry

[paul fellows]

here are 2 possibles for silencers for bench testing pulse jets!

1) take 2 circles of scrap metal (you could even use wood if it is kept wet ) with a radius of the same length as the exhaust pipe, make an hole in the centre of both large enough for the jet to come through unimpeded, place them together level with the end of the exhaust pipe, start the jet, move the circle that is furthest back backwards until it is at the same frequency as the jet. this will not interfere with the jet for bench testing . but it would be murder on the aerodynamics and power to weight ratio if you try to fly it
the way that this will lesson the sound of the pulses ( but not the noise of the jet ) is that once tuned the sound of the pulses will be coming from the circumference of the circle, so the sound from the point closet to you will be exactly out of phase with the sound coming from the point furthest from you, and these should cancel each other out. there will be two point ,'top' and 'bottom' , from which the sound dose not cancel at all. and between these two extremes there will be various degrees of cancelling.
of cause if you place your head at the centre of the circle you will hear the sound from all point at the same time

2)this aplyes to any type of jet. take several circles of thin workable metal, 5 or 6 times the diameter of the exhaust pipe, and cut a hole about 2 pipe diameters in the middle of them, split them in to two equal piles. Bend the disks in one pile over a solid sphere such that they form part of a spherical surface. Do the same with the other pile but use a sphere of a different size. Stack them 'dome' side up one at a time from alternate piles. Fasten them together and pack the out side gaps with wet rags or other non-combustible sound absorbing material (rock wool ).

[paul fellows]

Something from the weird and wonderful world of microwaves.

A signal (wave ) passing down one of two parallel conduits will produce a similar signal in the other conduit travelling in the same direction if they are connected by two holes a quarter of a wave length apart.

Could this be a pulse jet compressor?

[paul fellows]

the simplest possible pulse jet !!!
it consists of two concentric cylinders; one of them open to act as the exhaust, and the other one closed to act as a quarter wave resonator. And a cone to direct the moving air on to the top edge of the inner cylinder!
That's it. That and a way to fuel the system!

Its operation is basically that of a Galton whistle or even an old fashion police whistle scaled up.

Air flowing in hits the sharpened edge of the top of the inner cylinder and must flow ether into the central space or the outer space. and the system starts resonating. Forcing the air to flow; into the centre, down the outside, into the centre, down the outside, into the centre, down the outside, and so on!
If the whistle is to simple an example think of a recorder an edge tone with a length of pipe.
For those who want to go really fast look up the Hartmann generator it is about the same thing but without the cone, but would only work at high speed.

[paul fellows]

To any one injecting water or steam or thinking about doing so to get more thrust

you might like to think about this.
make emulsion of cooking oil, or similar, with water and inject that. at the temperature of a running pulse jet this mixture will be broken down to carbon monoxide and hydrogen . If there is not to much oxygen present This is known as the water gas.

A lot of the 'exhaust' of the Saturn 5 rocket was hydrogen from deliberate incomplete burning of its fuel. The reason for that was that hydrogen can be accelerated to a higher speed.

And a higher exhaust velocity equals more thrust!

Warning
hydrogen flames are hard to see! but are hot!

[tufty]

And a higher exhaust velocity equals more thrust!

No, higher massflow equals more thrust.

[WebPilot]

 If you pay attention to your units, Paul, you won't say things like this in the future:

And a higher exhaust velocity equals more thrust!

 The units of velocity, m/sec, are NOT units of thrust, Newton or kg∙ m / sec²

• momentum is defined as mass × velocity
• impulse (thrust × time) is the change in momentum.
• average thrust is the total impulse ÷ duration

 In the mks system of units, the unit for impulse is the Newton· second

 Please read Model Rocket Engine Facts, for more info.

 This all stems from Newton's Law,

        F = dp/dt = d(m · v)/dt

  where thrust is defined as the time rate of change in momentum.

[paul fellows]

 If you pay attention to your units, Paul, you won't say things like this in the future:

And a higher exhaust velocity equals more thrust!

so i got the units wrong?
the point i was making was that nasa like to have a lot of hydorgen in there exhaust,
and that by using the 'water gas reaction' excess fuel+steem+heat. it aught to be posible to do the same

[tufty]

 If you pay attention to your units, Paul, you won't say things like this in the future:

And a higher exhaust velocity equals more thrust!

so i got the units wrong?

No.

[paul fellows]

i don't want to argue maths, as i will loose evey time
but
here is a formula that i do understand!

half mass times velocity squaired
1/2 m V 2

that is the formula for the kinetic energy that as been given by a jet to the gas molicules coming out of the tail pipe, and the same must be acting on the jet.
so for two jets both with the same mass of exhaust, the one with the highest exhaust speed must experince the largest Newtonian reaction as a result of the higher kinetic energy of its exhaust gasses.

is there anyone out there with a jet that they can put more fuel into than it can normaly burn, and witch they can inject steem into. can i begg you to prove me right by ,
starting with the jet at full throttel
slowly add both excess fuel and steem
use the throttel and the steem valves to get the mixture about right
gradualy add more fuel and steem, being carefull not to cool the jet to below 1000 degrees
do you get a cool looking after burner type flame? that will be the hydrogen!
more importantly do you get more power out then you would have if you had just injected that amount of steem?

[paul fellows]

over on the rocket part of the site they want low mass products for there exhaust
also i found this on wikipedia
The thrust from a jet engine is determined by the velocity of exhaust gases measured relative to the engine.

The velocity of the exhaust gas as it leaves a jet engine is :[1]



where

is the specific enthalpy of the gas leaving the turbine and entering the propelling nozzle
is the specific enthalpy of the gas after it has left the propelling nozzle

that has not copyd well the page is http://en.wikipedia.org/wiki/Jet_engine_performance

[Thor]

To any one injecting water or steam or thinking about doing so to get more thrust
A lot of the 'exhaust' of the Saturn 5 rocket was hydrogen from deliberate incomplete burning of its fuel. The reason for that was that hydrogen can be accelerated to a higher speed.

Rubbish Paul.
That is poor engine efficiency.Do some thorough research you will see where you are wrong.

i don't want to argue maths, as i will loose evey time
but
here is a formula that i do understand!

half mass times velocity squaired
1/2 m V 2

that is the formula for the kinetic energy that as been given by a jet to the gas molicules coming out of the tail pipe, and the same must be acting on the jet.
so for two jets both with the same mass of exhaust, the one with the highest exhaust speed must experince the largest Newtonian reaction as a result of the higher kinetic energy of its exhaust gasses.

Paul with all due respect.[Bolded] If that is your argument than quit using terms allocated to fields where they do not belong.
As for the rest.You have the system completely mixed up.
Kinetic energy brought on to the medium being accelerated does not equate to the increase in thrust but rather it is but one factor that is part of the cycle efficiency of a engine.

Research first and foremost, posting latter is my advice to you.

[paul fellows]

well Thor
your style of dealing with people is rather abrupt.
and i personaly im not inclined to put a hole lot of creadance in some one who hides behind the sudoname of some one who dose that to goats

[tufty]

Thor may be "abrupt", and what he does with goats is his own business. However, he's absolutely right.

Research first and foremost, posting latter is my advice to you.

The answer to why you're wrong has been posted at least twice in this thread, once (again rather abruptly) on the 26 March by myself, and then again, with significantly more detail, by WebPilot on the same day.

[paul fellows]

sorry
i was a bit to cross with thor
it is just i have been trying to get some one to help me understand pulse jet theory and geting not a lot of suport.
so when thor critizised me for not doing enough reseaserch, when he had not thought enough about the sudoname he was hiding behind, i felt slighted.
for the record what the mythical pagan god Thor did with goats is, he had two of them pull him around in a cart.
yes Thor is a two goat power god