PyroJoes Recipe for Beginners

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PyroJoe
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Wed Mar 07, 2012 8:33 pm

Looking good, those elbows look better that way. :wink:

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Re: PyroJoes Recipe for Beginners

Post by metiz » Wed Mar 07, 2012 9:27 pm

The cc volume on both engines look crazy small, are they the right volume or should the cc's compensate for the shorter choke cone
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Wed Mar 07, 2012 10:15 pm

Remember it is three engines stuffed into 1.

That does look correct. I think you will understand more when you throttle the tiny 50 to full glow.8)

I would guess the steep angle on that choke cone makes it look short.

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Re: PyroJoes Recipe for Beginners

Post by metiz » Thu Mar 08, 2012 7:57 pm

I've got a friend that wants a scaled down version of (GRIM)Joe's snorkler. I calculated the diameter of the cc, asuming it was round, and it's way bigger than you'd expect from the caliber method. The caliber method dictates a cc at about 82mm, the actual cc is close to 140. Is there a reliable method for scaling this engine (and keeping the no air start feature?)

I think 2/3rds of the original size would be ideal. That would make it about waist-high
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Thu Mar 08, 2012 11:33 pm

It should scale down 2/3 ok, the CC is somewhat relaxed. It is slightly more fussy than the caliber method with a matching intake to tail ratio, getting the injector correct to have the entire range takes some effort.

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Re: PyroJoes Recipe for Beginners

Post by ganuganu » Fri Mar 09, 2012 1:41 pm

PyroJoe wrote:Attached is a scale down of the big one to have a 50mm tailpipe. (I say give the steep cone a try)
From what I have seen, valvers by default are typically 3 blended bodies. Our valveless ones have some catching up to do.

The good news here is we don't have to worry about pressure crushing the valves, or the core gas turning them to liquid metal. We can leverage up the pressure and temperature beyond the point valves would fail.
is this an Helmholtz combustor type? your CC and choke lengths differ greatly from other designs.

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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Mar 09, 2012 2:13 pm

It is close to some existing designs, with the exception of intake to tail diameter ratio, and length of course. I say its in good company.
Attachments
Kentfield.jpg

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Re: PyroJoes Recipe for Beginners

Post by metiz » Thu Mar 29, 2012 9:42 pm

Build it in about 5 hours, don't know when I'll test.
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100_2992.jpg
100_2990.jpg
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Re: PyroJoes Recipe for Beginners

Post by ganuganu » Fri Mar 30, 2012 2:22 am

wow metiz engine looks great and i should say you have got a good welding experience.

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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Mar 30, 2012 4:18 pm

Looking great. I have built several of these blended ones in linear form, curious to know how it does with the backward intakes. Mine typically start at low amplitude and build as more fuel is added.

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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 6:00 pm

Over the next few posts I will attempt to explain "aerodynamic valving". This is my own thoughts on the matter and not comprehensive of all designs. As seen in the Lockwoods and many other designs, valveless pulse jets can run without much need for the effect. On occasion I violate the concept myself to check the robustness and stability of a design.

From what I have seen the advantages appear during the starting process, and when trying to achieve high fill ratios of the combustor with air fuel mixture. In many cases throttle range can also be increased.

Also engines that have no air entrainment from a fuel source or ram air may require the effect for sustained running. Otherwise a air hose or leaf blower may be required to keep an engine running that lacks the affect.

A good concept to look at before beginning is coefficients of flow for orfices.

You can somewhat see that as the entrance into a pipe or orfice becomes smooth and spread the flow is able to gradually enter the pipe or port without much resistance or turbulence or "self choking effect".
Attachments
orifice.JPG
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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 6:25 pm

If an intake port or pipe has a sharp edge, it creates a condition in that some of the air around the port has to enter the port at an angle that is very near perpendicular to the axis of the port (shown here in red). The inertia of the gas doesn't allow the gas to quickly turn the corner/edge, and the outer flow intrudes far into the center of flow in the port. This creates a congestion of flow in the port.
Attachments
CHOKE1.jpg

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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 6:39 pm

If we look at a intake that has a gradual radius that forces the side air to enter at a low angle, then the flow can proceed without much resistance or congestion. Nice and smooth.

This is why most members on the forum will instruct to "flare" the intake pipe to avoid problems during in flow into the engine. At times I will lightly sand the flare to insure no rough burrs or tool marks. Slippery as frog sweat.
Attachments
nonchoke.jpg
Last edited by PyroJoe on Fri Apr 20, 2012 9:08 pm, edited 2 times in total.

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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 6:52 pm

After a good in flow at the entrance has been achieved the flow will enter into the combustion chamber. Here (marked by red circles)I like to use a sharp edge that allows the intake flow to cleanly shear away from the intake port and continue deep into the chamber.

Notice here that the intake air temperature should be near cool ambient levels, and has high density compared to the gas that would probably be in the tail at the moment. Some offer that this aids in the intake valving to some extent, as well I think it does to some value.
Attachments
shear.jpg

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Re: PyroJoes Recipe for Beginners

Post by PyroJoe » Fri Apr 20, 2012 7:25 pm

Eventually the tail will start to achieve a flow into the chamber, not sure of when or if this is near accurate. The long slow cone allows the in flow from the tailpipe to enter without obstruction, very smoothly.
Attachments
meet.jpg

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