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Hybrid Fueling Question

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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Hybrid Fueling Question

Unread postAuthor: chaos » Sat Jun 23, 2007 8:32 pm

Ok so im gonna build a hybrid but i dont want to really build a fuel meter at the moment. so can i just spray pump and pray? or shoul i go the extra mile and make the meter?
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Unread postAuthor: VH_man » Sat Jun 23, 2007 8:35 pm

umm, ive never tried it, but from what it seems like it wouldnt be a good idea. from my understanding you need precise volumes, mixtures, and pressures to make the cannon actually fire.

make the meter.
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Unread postAuthor: hi » Sat Jun 23, 2007 8:58 pm

it would be VERY diffculy, but possible, maybe for Christmas God will let you take a shot with it, but dont expect it to work the first 1000000 tries.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: chaos » Sat Jun 23, 2007 9:00 pm

ok kool thanx guys, one more question... how big should i make the meter if say im using a 1' X 3" chamber?

thats all i need and i can start building
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Unread postAuthor: spudthug » Sat Jun 23, 2007 9:13 pm

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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: chaos » Sat Jun 23, 2007 9:17 pm

thanks mate i almost forgot about that tool
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Unread postAuthor: spudthug » Sat Jun 23, 2007 9:19 pm

hehe ur welcome.. if u need any help with it ill do it for u but it is really easy so i think u should be able to :wink: u should psot it on my site as well whe nur done :wink:
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: dongfang » Sun Jun 24, 2007 5:47 am

Make an athmosperic pressure fuel meter:

1) Get a transparent bottle, big enough to hold the max amound of fuel you will need.

2) Measure 100 ml of water, pour it in bottle, cap it, it turn upside down, mark the surface line on outside of bottle. Turn bottle back to cap upwards, and write 100 at your line.

3) Repeat for 200, 300, ... etc ml until bottle is full.

4) Drill a small hole in bottom of bottle and through cap. Fit a thin hose through the cap (its end must not stick down in the bottle -- all the contents of the bottle must be able to exit through it)

5) Get some transparent container that can contain the bottle vertically, and has 2-3-4 times the volume of it. Make a fixture that holds the bottle right side up, install in container. Fill with water.

6) That´s it! You can now inject xxx ml of gas into the bottle, and it will displace the water by the same amount. The weight of the water will even pump the gas back out of the bottle, into whatever you connect the hose to. OK if that´s the cannon´s chamber, place the inlet LOW and also a small vent valve HIGH in the opposite end. Then, you will almost completely avoid sending the part of the gas through your chamber of out in the air. (propane is heavy).

This gas meter can be made highly accurate, and it costs peanuts.

The transparent container is not really necessary - you may use another piece of hose as a level indicator, and put it on the outside of the container. See my "Sonic bla bla - it´s feasible" thread in combustion forum. There is a photo. BUT use thicker hose for the level meter - I always get annoying bubbles in that small hose so I need to take it off to have them blown out.

Regards
Soren

Oh, and for your hybrid: First inject, say, 4 * 0.043 * V litres of gas. Then inflate to 4 bar. 4 is the ratio (charge pressure) and 0.043 is the mix ratio for profane, opps propane, as far as I remember.
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Unread postAuthor: noname » Sun Jun 24, 2007 11:36 am

The funnest way to make a hybrid is useing spray and pray. You spray in a bunch of propane, then get a very small volume pump. Pump once, click the igniter, pump one more time, click again, etc. You'd be surprised at how well it actually works. You just need a pump small enough to raise it like .5 psi per pump. I's also somewhat scary, because you never know when it'll shoot, but that makes it more fun!
Yes, I've done this. It was a tiny hairspray hybrid.
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Unread postAuthor: trae08 » Sun Jun 24, 2007 11:53 am

completly off topic but chaos i think that carp b gone video is pretty messed up
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Unread postAuthor: jimmy101 » Sun Jun 24, 2007 3:56 pm

dongfang wrote:Make an athmosperic pressure fuel meter:
...

6) That´s it! You can now inject xxx ml of gas into the bottle, and it will displace the water by the same amount. The weight of the water will even pump the gas back out of the bottle, into whatever you connect the hose to. OK if that´s the cannon´s chamber, place the inlet LOW and also a small vent valve HIGH in the opposite end. Then, you will almost completely avoid sending the part of the gas through your chamber of out in the air. (propane is heavy).

This gas meter can be made highly accurate, and it costs peanuts.


A minor nitpick. To get the gas in the bottle to be at atmospheric pressure the water level in the bottle needs to be the same as the water level outside the bottle. (We'll ignore the small amount of water vapor that'll be in the propane.) To get 100ml you need to raise the bottle until the 100ml marks is at the same level as the water in the large tub. Fill with gas to the mark. Then fully submerge the bottle to get the water pressure to pump the gas back out of the bottle.

The pressure in the bottle is 0.0361 PSI high for every inch (0.433 psi/ft) that the water level in the bottle is below the water level on the outside of the bottle.

Wouldn't want that 1/2% error per inch of depth messing you up. :D
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Unread postAuthor: dongfang » Mon Jun 25, 2007 4:24 am

Hi Jimmy,

That's right, the water will compress the gas a little.

(in Metric, we say 1 bar is 10m water column ... so there will be about 1% more pressure for each 10cm = 10m/100 of gas column in the water bath. Easy huh ;)?

Of course one could compensate for that when calibrating the thing .. or, more sanely, just ignore it ;)

Soren
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