SpudFiles

Hi!
I am new here and i want to build my first hybrid cannon.
I have a question about mixes. I want to use propane as a fuel but i don't know the ratio of it to air. For example if i want 10x atmospheric mix how much air and propane i have to add?
Also i want to know why nobody (at least i did not seen it on internet) not using mixes more than 11x? Is it too dangerous or there is any other problems with higher pressure?

Welcome to the forum!

Regarding fueling hybrids, I recommend looking here: http://www.spudfiles.com/hybrid-cannons/topic13602.html

My preferred method is using syringe injection, though this is only practical for smaller chambers:

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For a hybrid mix, just multiply the resulting fuel volume by whatever mix number you want to achieve.

It's important that you consider the dead space after the check valve of your pump to be part of the chamber volume when making your calculations, especially for small chambers.

The calculation is as follows:

(ideal fuel % / 100) x (chamber + pump dead volume) x mix number


In the case of this Beto shock pump, the dead volume is 1.75mL. For a 50mL chamber using propane to say 10x, the calculation is as follows:

4.2/100 x (50+1.75) x 10 = 21.7mL of propane

After the fuel is injected, all you have to do is pressurize with your pump to the following pressure (assuming you're using psi):

(mix number - 1) x 14.7

In the case of our 10x mix, the calculation is as follows:

(10-1) x 14.7 = 132 psi

If your gauge can read bar, simply pressurize to (mix number - 1) bar, so 9 bar in this case.

Also i want to know why nobody (at least i did not seen it on internet) not using mixes more than 11x? Is it too dangerous or there is any other problems with higher pressure?

It is not dangerous as long as your chamber and barrel are strong enough to take it.

Here is a rather long thread tracing my personal development of smaller hybrids up to 28x.

Up to 16x or so a simple piezo ignitor can suffice, more than that and you need more powerful ignition.

Thank you for answer!

Consider downloading Hybrid Gun Design Tool to simulate your launcher before building, it will help to optimize the design as well as making sure that the materials you select are up to the task of safely containing the pressures generated.

I already downloaded it) One more question i have. I just found out that there is no clear propane in Russia, it is all mix of propane(60%) and butane(40%). Maybe it is every where like that, i don't know. Anyway, the question is: will the proportions for propane that i read in hybrid fueling thread work for propane and butane mix? If not, please, tell me ratio of propane(60%) and butane(40%) mix to air.

And won't it be better if i will use an oxygen instead of air?

Here is the chamber that i want to use. 19.2 inches long, 2" diameter, 60.3 in³ volume. I think it's gonna be a mighty cannon. HGDT expects 722 ft/s with 3.9 oz 1.25" projectile(steel ball) at 7x mix.

The explosive limit of butane is 1.8 to 8.4%, while for propane it's 2.9 to 9.5%, so they are in a very similar range. Aim for approximately 4% for the best performance.

And won't it be better if i will use an oxygen instead of air?

Better for performance, yes, but extremely dangerous. I highly recommend not messing with oxygen.

Here is the chamber that i want to use. 19.2 inches long, 2" diameter, 60.3 in³ volume. I think it's gonna be a mighty cannon. HGDT expects 722 ft/s with 3.9 oz 1.25" projectile(steel ball) at 7x mix.

That looks like it will take the strain, what's the material and wall thickness?

For a tank that size my syringe method is a little impractical as you need to inject almost 3 liters of fuel at atmospheric pressure for a 7x mix! Manometric metering would be more feasible.

Also with a muzzle energy of almost 2000 ft lbs, make sure you have a safe place to shoot that ball because it's going to go some distance...

Chamber is steel with about 2.5mm wall thickness. Earlier on i made an air rifle with 1/2" diameter and 18" long steel chamber(approximately the same wall thickness) that i've been pumping up to over 200 bar and it holds absolutely fine. In case with my hybrid, HGDT predicts maximum pressure of 100 bar at 10x mix. I probably will not do more than 9x mix because my compressor can't generate more than 8 bar pressure so i think it is pretty safe.

Yes, i am gonna use a manometric metering.

I have a safe place for testing and plenty of thick wood for making a strong backstop.

What about oxygen, i still want to try it(yes, i am crazy). If i will, i will probably make a distance ignition to not be near the cannon if something happens or wil try it on lower mixes first. Anyway, if i will do those experiments, i will do them after succesfull testing with normal propane/air mix.

What about oxygen

Here are some scary pictures of airguns that were filled with oxygen to convince you:









Note that no attempt was made to have ignition here, it was simply the fact that an oxygen-rich environment made it easy for the lubricant to burn, violently.

If you still want to play with oxygen, read through this thread: http://www.spudfiles.com/hybrid-cannon- ... 15524.html

I first tested the cannon with oxy-propane up to 40x and then with air-propane up to 190x.
When i used oxy-propane i tried to replace all the air in the chamber with oxygen before adding the fuel to increase the power, but instead of that i got a really bad shoot and i am almost certain that i got DDT.
Because when i recovered the steel projectile i noticed that a piece of the brass burst disk had embedded itself almost a half mm into the back of the projectile.
Even at 190x with air-propane i haven't got this problem , so i think its the Nitrogen in the air that's prevent DDT from happening

No reason to put yourself in unnecessary danger for no performance benefit.

Well, you probably right. Thank you for advice!

Vadim wrote:Well, you probably right. Thank you for advice!

Я могу помочь.Я уже делал гибриды,даже не один,увлекался этим. Напиши https://vk.com/id111087416

I had thought about enriching the mixture of my hybrid with a bit of oxygen only, not everything, but after seeing this and seeing something else on the web, I do not think I tried it