PyroJoes Recipe for Beginners

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PyroJoe
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 7:32 pm

I somewhat have accepted the idea that ignition occurs typically in the back of the engine and works its way forward, probably with a slight pressure wave ahead of it. The incoming air charge starts to pile up against the forward moving front until intake flow slows.
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 7:41 pm

Eventually the intake flow will stop when events have changed the parameters at the chamber port.
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 8:02 pm

Now with the intake port having a sharp edge it creates congestion in the intake/head port, while the port leading into the tail is at a very low angle. This creates a bias for the most of the flow created by the deflagration event to flow through the tail port.

The density of the gas trapped in the tail is lighter than the intake so the path of least resistance again tends to be the tail port.

The 0.88 caliber intake also adds to the effect, so there is a buildup of all three parameters biasing towards the tail, radius, gas density and cogestion of the intake.

One can see how this would limit the effects of intake leak and allow marginal performance from an engine without an augmentor.
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 8:16 pm

Occasionally I have reported of a side wall intake leak, This is when the intake is in close proximity to the sidewall of the chamber, and what is happening is part of the intake is flowing freely without congestion. A few engines wont even sustain operation with this type of leak.

Although a side leak works good for driving a tailpipe. I think the effect can well be seen in GRIMS draft engine, along with many back-enders whos tail is offset to the side of the chamber, and the intake has plenty of congestion from the headplate.
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 8:33 pm

For something like a sphere is more difficult. It would require the transition from chamber to tail to have some radius to it, so the flow would be biased to the tail without congestion(blue). The intake/chamber port would need to be sharp on the inside to aid in valving (red).
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Re: PyroJoes Recipe for Beginners

Post by ganuganu » Sat Apr 21, 2012 11:39 am

Pulsejet animation made by me yesterday. i think it makes a better understanding.
http://www.truploader.com/view/522862

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Re: PyroJoes Recipe for Beginners

Post by Storm » Sun Apr 22, 2012 10:29 am

Ganuganu, is this idea that the velocity of the exhaust gas is faster than the intake gas true?

Also your animation explains no aerodynamic "valving" as PyroJoe was pointing out.

Thankyou PyroJoe it is very easy to understand, I was thinking of using a concept to create a vortex to increase valving which has been noted by others before but I've not heard of any results. Where Logan side ports are offset to the perimeter, now your drawings indicate the opposite outcome would be acheived with linea engines but I still wonder if the vortex momentum would continue during the explosion and overcome the sidewall effect.

Image
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Re: PyroJoes Recipe for Beginners

Post by ganuganu » Sun Apr 22, 2012 3:15 pm

Storm wrote:Ganuganu, is this idea that the velocity of the exhaust gas is faster than the intake gas true?

Also your animation explains no aerodynamic "valving" as PyroJoe was pointing out.

Thankyou PyroJoe it is very easy to understand, I was thinking of using a concept to create a vortex to increase valving which has been noted by others before but I've not heard of any results. Where Logan side ports are offset to the perimeter, now your drawings indicate the opposite outcome would be acheived with linea engines but I still wonder if the vortex momentum would continue during the explosion and overcome the sidewall effect.

Image
iam not about to explain the aerodynamic valving, just to make understand the working inside the engine. There is no good animation in the net so only i did it. :)

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Re: PyroJoes Recipe for Beginners

Post by Storm » Sun Apr 22, 2012 4:53 pm

Ok so does the exhausting gas through the tail move at a higher velocity than the exhausting gas through the intake as in ganuganus animation?

I thought this one by Eric Beck was very good!
http://www.youtube.com/watch?v=cFK2B6txOL8
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Mon Apr 23, 2012 2:10 pm

From what I've read, speed of sound does increase as the temperature of a gas is increased. Also the gas composition can affect the speed.

Even if the gas speed of the exhaust is twice as fast as the intake, you can see that the intake will allow the escape long before the exhaust reaches the end of the tailpipe. Thats where the intake leak occurs.

ganuganu, thats a neat illustration. If it is easy to create the illustrations, show the exhaust speed slightly higher than intake speed, and add augmentors. That would be a interesting to watch.

I am not sure if vortex will add anything to the valving. I think the flame front won't have much problem propagating through and building the pressure. My thoughts are as the pressure is increased, the vortex wont have as much affect as the aerodynamic valving. I think the flame front can travel sideways through a vortex formation, if that makes sense.

With what you have drawn there, I agree that the outcome is near opposite, the intake port is stretched around the perimeter so the congestion is less, and the tail pipe is sharp, so it produces more congestion. It becomes more difficult to start and the fill ratio will decrease. It may be possible to offset the intake slightly more centered, and put a good radius on the tail pipe. That would help.

The radius of the intake could be reduced to below the 0.88 caliber but be aware the frequency and fill ratio will suffer as that radius is reduced.

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Re: PyroJoes Recipe for Beginners

Post by metiz » Sat Jun 23, 2012 3:28 pm

Thought this was interesting. I ran the triple intake at a friends house. He had some NOx lying around and we decided to inject it into an intake when the engine was running. The engine's pitch goes up, does that mean it's running leaner? We never got the engine up to full throttle due to an early abort. The "what the hell are you doing" kind. Anyway, with NOx injection, the maximum throttle should go up right? http://www.youtube.com/watch?v=9gQRvX1gTvg
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Re: PyroJoes Recipe for Beginners

Post by InventorZeke » Fri Nov 22, 2013 9:54 pm

This is an incredible guide! With just the desired intake diameter I was able to in five minutes calculate all other values without having to half-assedly scale a random design.

I have a question that may seem odd as it is counterintuitive. The intake diameter I require is 2"; dividing by 0.88 for a caliber of 2.72" and intake length of 6".

Let's say that I want to put a thin (.25") baffle in the middle of the tube constricting it to an I.D. of 1.75" just at that point. Since 1.75/2.72 is .77 and within the 0.75-0.88 range, am I correct in assuming it will still function properly?

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Re: PyroJoes Recipe for Beginners

Post by RC Man » Fri Nov 22, 2013 10:39 pm

InventorZeke,
There are just a few people left in here, from the last couple a years.

Have ya ran a Valveless PJ yet?
If so, than ya know,. its a test and tune thing here. I myself have tried a venturi in the intake, to get the airspeed up, to suck gas up the intake tube faster.
If ya just put a reduction in the intake, you could get higher speed through the intake, But testing, is everything here.

I put a PJ together today, just to check PyroJoes calculations, and it ran, but with my gas supply, and my regulator, it didnt make much thrust. (Regulated gas regulators dont work for what we need)
Tomorrow, I will build a unregulated fitting and go for it all...... PJ Pumper.

Airspeed, and atomization of the gas is what we need to get a PJ Motor up to specs.

Just my 2ct.

Frank

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Re: PyroJoes Recipe for Beginners

Post by InventorZeke » Sat Nov 23, 2013 8:39 pm

RC Man, I have never so much as seen a pulse jet in person; I have however spent numerous hours researching all I can find on both valved and valveless of all designs.

While a simple venturi would imaginably increase velocity, I'm thinking that the baffle may create some cool toroidal vortices.

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Re: PyroJoes Recipe for Beginners

Post by RC Man » Thu Nov 28, 2013 9:31 pm

toroidal vortices, What a cool name for a smoke ring, lol

Where are ya from ? InventorZeke ?

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