Odd thoughts on how it works

decook1110 · Post by **decook1110** » Sat Mar 20, 2004 1:32 am

On a side note while Luc is struggling with his 130R I thought I would fire up a discussion on the pressure jet in general. I'm going to through some thoughts out there and get some feedback. As a disclaimer I am not a vibrations or acoustical expert.

I think the acoustical tuning on the G-8-2 is strictly a bandaid to stabilize the flamefront, I don't believe it does anything to the engine cycle which would increase either its thrust or efficiency. What I mean is that if the engine had a stable flame front without all the harmonics lining up and all the tuning issues and noise, it would still make the same thrust. By definition a pressure jet uses the dynamic pressure from the velocity of the incoming gases to build pressure in the combustion chamber, fuel and air are burned at this higher pressure and then the pressure is used to accelerate the now hotter and lower density gasses to a higher velocity (than the incoming gasses had) leading to thrust. The higher the pressure in the combuster, the better this system works and the higher the efficiency. The best pressure ratio I came up with for this system was 1.2 which is why this cycle is a dead end for a propulsion system on an aircraft compared to a turbo jet which at worst has a pressure ratio of 6.

If my theory is correct, we could do away with all of the tuning issues and have the same thrust if we could stabilize the flame front some other way. Back when I was looking into these engines and reading all that I could get my hands on, I came across a paper at University of Michigan Ann Arbor on combustion stability of propane in ducts. I keep trying to find it again, but I lost it. Anyway its point was that as the inlet impedence when up, it was harder and harder to stabilize the flamefront. The G-8-2 has the flame front right past the mouth of the 3rd stage, you don't get much higher impedence than that.

Well do you agree or disagree that the tuning and noise only add to stability and not to thrust directly?

This also leaves two possible options for why Lucs engine won't perform. 1 is not enough average velocity of the incoming gasses to overcome the pressure increase in the combustion chamber (the nozzle momentum transferred to the air flowing into the 3rd stage not enough) or as your vibration analysis seems to show, another vibration from maybe the coils throwing off the tuning and causing flamefront instability. Mr. Wheeling found this on his airplanes, he could never get the engines to both operate at the same time near each other.

Dave

Viv · Post by **Viv** » Sat Mar 20, 2004 12:18 pm

I am still learning about this engine Dave, I only started on it a couple of months ago when Luc came on to the forum and asked for help, previosly I had ignored it but since I realised it has a nimber of attractions for the amatuer.

The biggest problem is all the disinformation that people with vested interests in it have promoted, smoke and mirrors, they make varios claims about how it works but when you check out the basic physics you find its pure fiction.

I admire your attempt to boil it down to basics and start again, and I for one will help as much as I can.

Your last comment regarding Mr Wheeler is the critical proof that the engine has resonant acoustics present, pulse jets engines also do this as a matter of record.

I agree the acoustics are used to stabilise the flame front, but I would not discount any additional compression that results.

Any high power flame front will produce noise on a broad spectrum, it will not be white noise as that has an even amplitude, any engine structure will have a number of frequencys that it will resonate at, the noise power from the flame front will make the engine structure resonate strongly at those prefured frequencys.

So you cant have a flame front with out a god awful amount of noise energy being produced, Eugenes genius was to use it to help his engine along, also you cant have that much noise energy in a structure with out the structure being driven in to resonance (when its simple tubes that is).

The pressure jet is built like a violine, each and every part has its own particular note that it resonates too when struck, all of these parts together give the rich tone of the finished instrument.

Viv

Raymond G · Post by **Raymond G** » Sat Mar 20, 2004 9:08 pm

Dave, Viv,

Getting at the physics of these engines has been a long quest for me. If you model them simply as a ramjet, with a fuel jet induced airflow, then they are pretty easy to analize, and I agree with Dave's assesment of a max pressure ratio of 1.2:1 (I get 1.26:1 with a 165 psi, 1200 F resevoir). But I am not convinced that this model is correct. I believe that the resonances of the various tubes act to sonically 'supercharge' the flow.
We know that these tubes act as resonators. We also know that in a resonating tube, we get a peak wave (and peak pressure and min velocity) in the middle of the tube and that the pressure rise is proportional to the acoustic energy (i.e. dBa). Since the pressure jet is quite loud, it is not unreasonable to assume that the pressure rise from the acoustics is significant and may even be larger than the modest pressure rise from the fuel jet KE. This mechanism could result in significant thrust and SFC improvements over the simple induced ram jet model I mentioned above.

Regards,
Raymond

Mark · Post by **Mark** » Sun Mar 21, 2004 12:55 am

http://www.zex.com/information/products ... amplifier/

Here's a pressure jet theme for an oxidizer.
Mark

Mark · Post by **Mark** » Sun Mar 21, 2004 12:59 am

Banana Breath Amplifier http://www.exair.com/airamplifier/aa_applications.htm

Mark · Post by **Mark** » Sun Mar 21, 2004 1:04 am

http://www.vaccon.com/air.html#how

http://www.vaccon.com/air.html

Just some food for thought, nothing earth shaking but interesting to some extent.

Andrew Parker · Post by **Andrew Parker** » Sun Mar 21, 2004 9:11 am

I can't help but think about the Gluhareff pressure jet when I look at the Bodine patent illustrations (US2731795). He proposed a side ported pulsejet with the intake tube tuned to fool the main tube into treating the port as a solid wall. I have always wondered if you could take the gluey and remove the first and second stage tubes, leaving the 1/4 wave tube at the side port. You would need a blower, or a valve, to induce the flow through the side port into the main tube and you would have to probably change the fuel injector set up in order to maintain the proper stoichometric(?) mix.

I hope that Luc didn't destroy his creation in a fit of rage. It should make a great test bed for a number of variations on the theme, even if it has to sit in storage for awhile.

Andrew Parker

Graham C. Williams · Post by **Graham C. Williams** » Sat Apr 10, 2004 6:55 pm

Hi.
A lot of you have spoken about a 'stable flame front' or similar in connection with this motor. Can someone tell me why you should have a stable flame front, what is the purpose of a stable flame front? In what sense are you using the term?
This motor is a non-steady combustor. Non-steady combustors are designed to utilise combustion instabilities. It seems to me that for best combustion you want a highly unstable flame front, highly distorted in a turbulent flow.

Graham.

Graham C. Williams · Post by **Graham C. Williams** » Sat Apr 10, 2004 10:35 pm

Another question.
Why has the motor got the pointy front? Not the facile answer please.

Graham.

decook1110 · Post by **decook1110** » Wed Apr 14, 2004 3:49 am

That is the debate on these engines. It is my opinion that the engines is a 'steady' burner that has continuous combustion similar to a turbojet. It uses the dynamic pressure of the incoming propane and air to create its pressure ratio and generate thrust. The reason all the acoustic fiddeling is neccessary is because the high impedence (short 3rd stage) intake makes for unstable burning with propane. Somehow the acoustic tuning has caused the flame front to stabilize when it wouldn't other wise and makes the whole contraption work. That is what Gene did that was inovative. The shape of the nose doesn't have to be pointed except for external aerodynamic reasons. the volume of the nose probably has an effect, but not the shape. I believe that was covered in the

luc · Post by **luc** » Wed Apr 14, 2004 1:18 pm

Hi Guys,

Reading the forum this morning, I got interested in Graham questions. Soo ... here are my answer ... Graham.

Another question.
Why has the motor got the pointy front? Not the facile answer please.

That an easy one ... Graham. The cone is a dissonant resonator. One of the feature of a dissonant resonator, is that it inhibit the possibility of chock by his ever changing section. Now as you all know, chock is a high pressure area and a waist of energy. It also produce alot of heat. I also beleive that it ack like a Radar dish, where it focus the high and low pressure area.

Mannnn .... Master Viv will sure be proud of is young Padawan ... He he he.

As for the flame front stability ... I will refrain my self in posting on that. I know the answer, but it is too soon for that. In the other forum, I have made you guys a promise ... A promise that I will keep. But not now ... I can't for now.

Cya,

Luc

www.pulse-jets.com

Odd thoughts on how it works

Odd thoughts on how it works

Flame Front

Why?

Steady Combustion

Flame front and cone