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Continuous Fuel/Air Supply Idea

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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Continuous Fuel/Air Supply Idea

Unread postAuthor: skyjive » Wed Oct 13, 2010 10:30 pm

Having skimmed though others' ideas, I think certain similar ideas have been proposed, but since I'm new to combustions I'll ask about my specific idea anyway.

Image

You have supply lines from pressurized air and propane tanks running through regulators set to a common pressure (say 20 psi) into a mixing tank, which then feeds the chamber when required. Additionally, a needle valve is included in the propane feed line, so after some experimenting you could get the relative flow rates to give you a close to stochiometric mix. The advantage of this system would be that the mixing chamber would automatically refill with a perfect fuel air mixture whenever pressure dropped below regulator pressure.

Is this feasible?

Has anyone come up with another way of providing a continuous fuel/air supply (analogous to that provided to an internal combustion engine)?
All the ways I've read about seem to just be one at a time static solutions.
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Unread postAuthor: Technician1002 » Thu Oct 14, 2010 12:23 am

It is feasible. You will want 2 regulators. One for air and one for fuel. You will want two metering orifices so the flow rate of both air and fuel can be controlled and in the proper portions. You don't need a "Mixing Tank". A simple T with the fuel air mixing as it flows will do nicely. This is the same way a soft drink soda fountain works. The 6:1 water syrup ratio is mixed right at the dispense nozzle as it fills your cup.
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Unread postAuthor: Moonbogg » Thu Oct 14, 2010 12:41 am

Yeah I think it will work. I had the idea but went an easier route becuase I didn't have the will to go through with it. Like tech said, managing flow is important as well as pressure. You can have a constant flow going to the combustion chamber, with greater flow for air than fuel. They will both stop flowing when the regulators kick in to stop the flow. Its a matter of managing the race to fill the chamber between the air and fuel. But once you get it down, you can have a really nice semi auto piston hybrid.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 14, 2010 12:54 am

Technician1002 wrote:The 6:1 water syrup ratio is mixed right at the dispense nozzle as it fills your cup.


Make it 7:1, stingy bastards... did you know that when serving with ice, the ratio is meant to be even lower, but it often conveniently forgotten :roll:
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Unread postAuthor: Technician1002 » Thu Oct 14, 2010 12:56 am

You will want to use "Precision" regulators for both air and fuel. A cheap plastic air tool regulator is not going to cut it.

If you don't need a high delivery pressure for a hybrid, a pair of BBQ propane regulators would work fine.

The syrup water ratio is for the liquid dispensed at the nozzle Melted ice is not compensated for.
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Unread postAuthor: D_Hall » Thu Oct 14, 2010 9:59 am

Yes, the concept works. We've a (roughly) 10X hybrid at the office that works with a system essentially identical to that.
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Unread postAuthor: POLAND_SPUD » Thu Oct 14, 2010 1:46 pm

Make it 7:1, stingy bastards... did you know that when serving with ice, the ratio is meant to be even lower, but it often conveniently forgotten
lol who cares.. it's just a soft drink, right? :wink:

Not a bad idea but I guess it would be better and simpler to use a 3 way to fill the chamber first with regged down propane and then with air.
Ohh jsr before you ask - I am working on my hybrid as we speak :D
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Unread postAuthor: Heimo » Thu Oct 14, 2010 2:32 pm

POLAND_SPUD wrote:I am working on my hybrid as we speak :D


seeing is believing...
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I took the liberty

Unread postAuthor: Technician1002 » Thu Oct 14, 2010 3:27 pm

I took the liberty to update the drawing. Flow meters are recommended for the gas and air for easy setup. Another option is to use it to fill a 2 liter pop bottle inverted with water in a tank. The rate to fill the bottle with air or fuel can be calculated by the time it takes to empty the bottle of water.

Both regulators should be set to the same pressure.

Flow regulators used for welding have a pressure regulator, needle flow valve and flow meter all in one convenient unit. One for air and one for fuel an you are all set. If metering a different gas than the meter is built for, you will need to compensate for the different gas density and scale the reading accordingly.

Pressure regulator with fixed pressure set, needle flow valve and flow meter in one nice unit.

EDIT: The regulator shown is fixed at a working pressure of 3.5 bar.
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Fuel metering.
fuelmixing.png (18.29 KiB) Viewed 932 times
Last edited by Technician1002 on Thu Oct 14, 2010 5:52 pm, edited 1 time in total.
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Unread postAuthor: Lockednloaded » Thu Oct 14, 2010 5:07 pm

the regulator will not fare well with such low flow propane, you'll need an expansion volume before the regulator
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Unread postAuthor: Technician1002 » Thu Oct 14, 2010 5:50 pm

For low flow I've never had a problem. This includes Coleman Propane lanterns, stoves, small heaters, etc. Only high flow applications need a vaporizer ahead of the regulator such as forklifts, large heaters, floor polishers, etc..

Edit, I picked up these for a future full auto Gumball Machine Gun. It will be used to deliver air and fuel for a timed duration for each shot to purge and charge the chamber.
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Flowmeter.JPG
Flowmeters. The yellow tube is calibrated for 2.0 SCFH of air at standard temprature and pressure.

The other one does not specify the gas, but it is marked at 6.5 full scale with a heavier ball and fatter tube. I'll check it later with air and a pop bottle.
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