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Hybrid ThorJack

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 12:19 pm

5x:
Air: 4.53 bar
bp: 1.5 bar
manometer reading: 1.5-1 = 0.5
feasible ...
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 1:17 pm

vidéo :

[youtube]http://www.youtube.com/watch?v=N11a-WnW1oE[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 15, 2012 2:30 pm

Two questions:

- are you purging the meter with fuel before hooking it up?

- when you hook up the meter to the chamber and open the valve, does the pressure on the manometer go up to the correct one for the mix? For example for 5x the pressure on the meter manometer should go up to 4 bar once you open the valve from the chamber.
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 2:35 pm

yes to purge

I did not notice ...

My French friends tell me that my mix is not good, it takes at least 6% and not 3.5% ... :shock:
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Unread postAuthor: MrCrowley » Thu Mar 15, 2012 2:37 pm

Have you tried physically shaking the cannon to get the fuel to mix inside the chamber? I have to do this on my smaller hybrid.

Edit: I would also suggest a spark gap smaller than 1mm. Mine must be about 0.2mm.
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 2:43 pm

Not physically ...

I made a flah ignition, so even with 1mm arc will
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 15, 2012 2:45 pm

MrCrowley wrote:Have you tried physically shaking the cannon to get the fuel to mix inside the chamber? I have to do this on my smaller hybrid.


I don't think that is necessary, the rush of air once the valve to the meter is opened should ensure a homogenous mix.

My French friends tell me that my mix is not good, it takes at least 6% and not 3.5%


I use a similar mix of propane/butane gas and work with 3.5%.

Combusion limits for propane is 2.4% to 9.5%

Combusion limits for butane is 1.9% to 8.4%

One test you can try is as follows:

Take a standard mix, say 6x.

Use the amount of fuel calculated for this mix, but use the air pressure for 7x.

If that doesn't work, try it again using the fuel for 6x but air pressure for 5x.

If either of these works, then your mixes are off.

After a misfire, do you fill the chamber with air again and vent before trying again?

Also, how accurate is the manometer on your fuel meter? If you calculare 0.6 bar, can you actually read that?
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 2:53 pm

ok for 3.5%
after the misfire I opened the chamber with the valve, I did not renew the air ...

My pressure gauge is graduated to 0.1bar
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Unread postAuthor: MrCrowley » Thu Mar 15, 2012 3:00 pm

jackssmirkingrevenge wrote:I don't think that is necessary, the rush of air once the valve to the meter is opened should ensure a homogenous mix.
I would have thought the same and I even got in to the habit of 'pre-charging' the meter with air (after fueling) to about 140PSI then opening the ball valve to the chamber and hoping the rush of air would mix the fuel up.

Perhaps given time, it will mix if just left on the ground but on two occasions I've tried to fire the gun unsuccessfully for about 40 seconds before shaking it around and getting ignition straight away.

ramses also had problems with mixing using his manometric meter, though I never have in Mjollnir.

Well there can really only be three problems here:
a) leaking
b) ignition
c) fuel

Leaking is pretty obvious to find and fix, Petitlu seems confident about the ignition and manometric fuelling is difficult to screw up. To restate JSR's question; how accurate is your fuel setup? Your fuel gauge shouldn't read any more than 30PSI and should have an accuracy of about 1.5% or less. When you come to adding the air for a 10x mix, do you add 132PSI on top of what is already in the chamber, so final pressure should be about 137PSI (or something like that, I'm not sure about butane)?

Something that may be worth checking: what is your local barometric pressure? Here it ranges from about 980-1030 (I think), which isn't much really only about 0.7PSI difference but it could be significant depending on elevation (though I think France is reasonably flat?).

Maybe I've forgotten something but I'm in a rush this morning, hopefully you'll have this sorted out before I'm back from uni :P
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Last edited by MrCrowley on Thu Mar 15, 2012 3:03 pm, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 15, 2012 3:01 pm

Petitlu wrote:after the misfire I opened the chamber with the valve, I did not renew the air...


Defintiely something you have to do, otherwise the unburned gas remains in the chamber so your mix will always be off.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 15, 2012 3:04 pm

This is how I suggested fuelling, see also attached diagram:

let's say you want to fill it to 10x.

let's say the chamber is 200cc (up to valve 1) and the total area in blue (including chamber, pipes, connections up to valve 2) is 250cc

a) connect the air supply (6 to 4)

b) open valve 1 and fill with air.

to calculate the correct pressure, you need a final pressure of 9 bar in the chamber (pressure = mix number - 1, in our case it is 10 - 1 = 9)

this means that pressure to fill the chamber is (total volume / chamber volume x final pressure )

in our case, this is ( 250 / 200 x 9 ) = 11.25 bar

c) close valve 1 and remove the air supply.

d) open valves 2 and 3 and purge the meter for a few seconds, then close valve 3.

e) connect the fuel supply ( 5 to 4 )

f) open valve 3

g) fill with fuel (valve 3 open, valve 2 open, valve 1 closed) to the correct pressure, calculated as follows:

First, we find the volume of fuel we need at 1 bar, this is (3.5 / 100 x mix number x total volume)

in our case, this is (3.5 / 100 x 10 x 250) = 87.5cc

The pressure we need to fill to is (volume needed / meter system volume x 1 bar)

in our case, this is (87.5 / 50 x 1 ) = 1.75 bar

be careful that this is *absolute* pressure; most manometers are reading 1 bar when the needle actually marks 0, so in this case you would fill to 0.75 bar.

h) close valve 2

i) open valve 1 and allow the pressure to equalise

j) close valve 1

k) disconnect the fuel system

l) you're ready to fire :D
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 3:13 pm

my chamber is 205cc (bottle + hose + connector)
meter 27CC
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Unread postAuthor: Petitlu » Thu Mar 15, 2012 5:38 pm

I did my lighting flash with two capacitors! I tried also in the room and it works well, the piezo is a ridiculous side ...

I will do other tests is required and there that it works!
It is on there will be no worries ignition already
So I'll be shooting at 3.5% and if its not working I am a 6% to see ...
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 16, 2012 12:06 am

Petitlu wrote:So I'll be shooting at 3.5% and if its not working I am a 6% to see ...


Try this:

One test you can try is as follows:

Take a standard mix, say 6x.

Use the amount of fuel calculated for this mix, but use the air pressure for 7x.

If that doesn't work, try it again using the fuel for 6x but air pressure for 5x.

If either of these works, then your mixes are off.


This gives you a slightly high and slightly low mix compared to what you are currently doing, to see if your calculations or metering are off.
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Unread postAuthor: Petitlu » Fri Mar 16, 2012 1:42 am

ok thank you!
I am testing by first air as you told me to do?

BBQ ignition or flash, I have two ..
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