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How exactly does a Hybrid work?

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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How exactly does a Hybrid work?

Unread postAuthor: HaiThar » Thu Sep 20, 2007 6:02 pm

I can't help but wonder how a Hybrid works exactly... I know it uses a combination of pneumatic and combustion systems, but as to how it actually fires, I am still perplexed....

Just a general idea would be GREATLY appreciated...

Thanks in advance...

I'z total :newb:
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Unread postAuthor: JDP12 » Thu Sep 20, 2007 6:08 pm

search... http://www.spudfiles.com/spud_wiki/inde ... rid_cannon

basically, for a 2x mix, you inject twice as much of fuel, and have twice as much of air in chamber... then ignite, use a burst disk... see some of the posts in this section.. there is one i think it's by some french dude, and see mine concerning air amount.

use a flyback ignitor for your spark if i were you
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Unread postAuthor: HaiThar » Thu Sep 20, 2007 6:10 pm

I'm not going to be building one any time soon... >_>...I'm still in the proccess of building my first pneumatic...

But thanks for the help! :D
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Unread postAuthor: noname » Thu Sep 20, 2007 9:29 pm

The easiest way for me to understand it, is that a normal combustions uses 4.2% propane. In a hybrid, you inject multiple amounts of propane. This brings the propane percentage compared to air much too high, and wouldn't ignite. So you ad compressed air until the percentage is back down to 4.2%.
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Unread postAuthor: paaiyan » Thu Sep 20, 2007 9:36 pm

The same ratio of air to fuel, but at higher than normal pressures. Ignition is pretty much the same as a regular cannon, though ignitors can become more demanding for higher pressures. The higher the pressure in the cannon, the more gas there is per unit volume, opbviously, this poses a problem for ignition as gasses are insulators. Therefore, higher pressures require higher voltages to get a good spark, that's where the stun guns and such come in.
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Unread postAuthor: psycix » Fri Sep 21, 2007 6:59 am

The idea behind a hybrid is to raise the pressure a few times to a few bar along with the multiplied amount of fuel in it and THEN igniting it.
This means a pressurised mixture explodes, raising pressure even more.
This causes the burst disk to break (the burst disc must be able to handle the initial amount of pressure) and the gun goes BOOM :)
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Unread postAuthor: jimmy101 » Fri Sep 21, 2007 11:08 am

Another way to think of a hybrid:

Goal: A "pneumatic" gun that operates at very high pressures, much higher than the typical compressor can generate.

1. Compressed mixtures or propane plus air can easily produce much higher pressures than your typical compressor. More fuel + oxidizer in the chamber creates more energy and pressure.

2. But, how do you keep the spud in the barrel after you've pressurized the chamber? Any pressure above just a couple PSI will pop the spud out of the barrel. You would like to charge the chamber to 30, 45, 60 PSIG (2x,3x,4x…) to get some serious pressure in the chamber. But the spud won't stay in the barrel with anywhere near that much pressure behind it, and the fuel hasn't even been ignited yet!

3. So, you need a valve to keep the pressure off the spud until you are ready to fire.

4. Cool, build a pneumatic gun. Instead of compressed air pump in fuel and air to raise the chamber pressure to say 2 ATM (2x) or more.

5. Ignite the mixture. You get high pressure in the chamber. A 2x mix should be in the vicinity of 200 PSIG at the pressure peak.

6. Now trigger your valve to apply the pressure you created in the chamber to the spud to launch it out the barrel.

7. The spud plops out of the barrel moving very slowly. WTF?

8. You created high pressure in the chamber by using the energy of combustion to heat the gases to a very high temperature. Ball park temp. of ~4000F. The energy in the chamber is really almost all in the heat, though you do have 2x, 3x ... worth of pressure from the initial pressurization of the fuel + air. Gases have a very low heat capacity and loose heat very quickly. In the couple seconds between igniting the fuel and opening the valve all of the energy in the gases has been lost as heat transferred to the chamber walls. You just can't open the valve soon enough after ignition to keep heat loss to an acceptable level.

9. Solution: A burst disk. You can think of a burst disk as an automatic valve. It will automatically open when the pressure behind it exceeds it's rupture pressure. So, you no longer have a delay between combustion and your manual triggering of the valve. You have nearly zero delay between the time when the chamber reaches high pressure and the automatic opening of the valve.

10. Ta da. You have a hybrid. Some of the energy comes from just operating the chamber at elevated pressure before combustion (2x,3x...). Some of the energy comes from the higher fuel + air charge in the chamber. To actually get it to work, you need a valve that opens automatically since manual control of the valve is much to slow. The issue isn't slow versus fast opening of the valve, the issue is the time delay between ignition and the opening of the valve.

11. A burst disk has the added advantage of being a very fast operating valve which usually has a large bore. So a burst disk is not only an automatic valve, it is also usually a very efficient valve.

12. One problem with a burst disk as a valve is that it needs to be replaced for each shot. Another problem is coming up with a suitable material for the burst disk. If it ruptures at too low of pressure you really don't get much out of the gun. If it ruptures at too high a pressure the gun won't fire the spud.
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Unread postAuthor: spanerman » Fri Sep 21, 2007 11:25 am

Great post!!!!

i tryed a coke can burst disc at 2x yesterday....was like a sloight pop then hssssssssssss, was pretty kool :)
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Unread postAuthor: Lentamentalisk » Sat Oct 06, 2007 9:25 pm

why not use a QEV with the pilot side just connected to the pump, but no trigger? then as soon as the goods set fire, the pressure in the chamber will be greater than that in the pilot area, which opens the valve and dumps the chamber.
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Unread postAuthor: noname » Sun Oct 07, 2007 12:00 am

That was an extremely vague explanation, but I think you're talking about how the first hybrid worked.
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Unread postAuthor: Rogue » Sun Nov 04, 2007 5:22 pm

jimmy101 wrote:Another way to think of a hybrid:

Goal: A "pneumatic" gun that operates at very high pressures, much higher than the typical compressor can generate.

1. Compressed mixtures or propane plus air can easily produce much higher pressures than your typical compressor. More fuel + oxidizer in the chamber creates more energy and pressure.

2. But, how do you keep the spud in the barrel after you've pressurized the chamber? Any pressure above just a couple PSI will pop the spud out of the barrel. You would like to charge the chamber to 30, 45, 60 PSIG (2x,3x,4x…) to get some serious pressure in the chamber. But the spud won't stay in the barrel with anywhere near that much pressure behind it, and the fuel hasn't even been ignited yet!

3. So, you need a valve to keep the pressure off the spud until you are ready to fire.

4. Cool, build a pneumatic gun. Instead of compressed air pump in fuel and air to raise the chamber pressure to say 2 ATM (2x) or more.

5. Ignite the mixture. You get high pressure in the chamber. A 2x mix should be in the vicinity of 200 PSIG at the pressure peak.

6. Now trigger your valve to apply the pressure you created in the chamber to the spud to launch it out the barrel.

7. The spud plops out of the barrel moving very slowly. WTF?

8. You created high pressure in the chamber by using the energy of combustion to heat the gases to a very high temperature. Ball park temp. of ~4000F. The energy in the chamber is really almost all in the heat, though you do have 2x, 3x ... worth of pressure from the initial pressurization of the fuel + air. Gases have a very low heat capacity and loose heat very quickly. In the couple seconds between igniting the fuel and opening the valve all of the energy in the gases has been lost as heat transferred to the chamber walls. You just can't open the valve soon enough after ignition to keep heat loss to an acceptable level.

9. Solution: A burst disk. You can think of a burst disk as an automatic valve. It will automatically open when the pressure behind it exceeds it's rupture pressure. So, you no longer have a delay between combustion and your manual triggering of the valve. You have nearly zero delay between the time when the chamber reaches high pressure and the automatic opening of the valve.

10. Ta da. You have a hybrid. Some of the energy comes from just operating the chamber at elevated pressure before combustion (2x,3x...). Some of the energy comes from the higher fuel + air charge in the chamber. To actually get it to work, you need a valve that opens automatically since manual control of the valve is much to slow. The issue isn't slow versus fast opening of the valve, the issue is the time delay between ignition and the opening of the valve.

11. A burst disk has the added advantage of being a very fast operating valve which usually has a large bore. So a burst disk is not only an automatic valve, it is also usually a very efficient valve.

12. One problem with a burst disk as a valve is that it needs to be replaced for each shot. Another problem is coming up with a suitable material for the burst disk. If it ruptures at too low of pressure you really don't get much out of the gun. If it ruptures at too high a pressure the gun won't fire the spud.


...WOW! thanks jimmy! that just completely explained it to me. thanks



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