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New Mini Hybrid

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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New Mini Hybrid

Unread postAuthor: Willdebeers » Sun Jul 17, 2011 9:41 am

After a long break from spudguns, I finally decided to do what I always wanted to do, and make a hybrid.

I haven't yet shot it, so was wondering weather to put this in the discussion or showcase. I decided the discussion as it is not yet finished.


Anyway, it is machined out of a solid aluminium rod. ID of the chamber is ~13mm. I expect to run it on 10-12x mixes.

Fuelling is what I am worried about, so it would be good to have some help with that. For burst discs, layers of tin foil seems to be working great.

And yes, this was heavily influenced by the HyGaC20 by Larda. I <3 that gun.

So without further ado, here are the pics:

The whole thing:
Image

The breach open:
Image

The Chamber:
Image

The burst disc holder:
Image

The gap is from the o-ring.
Image

Another pic showing the tee at the back:
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And another:
Image

6mm BB Barrel:
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Overview:
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Unread postAuthor: Mimikool » Sun Jul 17, 2011 9:58 am

Nice built ;)

You can use a meter to introduce the exactly amount of fuel. I thinks the propane have to occupy 4% of the mixture.

So build a pipe, which the volume is 4% of the chamber volume, and you put in the meter (the pipe) the same pressure as the final mixture. If you want 10x, you put 10bar of propane before open the ball vavle.

The propan becomes a liquid at 7bar, so you multiply the meter volume by 2 and divide the pressure by 2 ;) to have the same amount of fuel.

Then you insert the air ;)

What's your ignition?
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Unread postAuthor: Willdebeers » Sun Jul 17, 2011 10:02 am

Mimikool wrote:Nice built ;)

You can use a meter to introduce the exactly amount of fuel. I thinks the propane have to occupy 4% of the mixture.

So build a pipe, which the volume is 4% of the chamber volume, and you put in the meter (the pipe) the same pressure as the final mixture. If you want 10x, you put 10bar of propane before open the ball vavle.

The propan becomes a liquid at 7bar, so you multiply the meter volume by 2 and divide the pressure by 2 ;) to have the same amount of fuel.

Then you insert the air ;)

What's your ignition?


My ignition is a peizo, nothing special. Stunguns & other HV circuits are illegal in the UK, so not much luck there. My spark gap is <1mm so I should be good there.

Even if I had 2 1/4" ball valves connected with a close nipple, it would still not be 4%, so I may need to do a little maths to get the correct mix.
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Unread postAuthor: Mimikool » Sun Jul 17, 2011 10:10 am

When you increase the pressure, the spark lenght decrease, a simple piezo not be sufficient i think.

Yes, it must find the compromise pressure/volume to have the right amount of fuel.
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Unread postAuthor: ramses » Sun Jul 17, 2011 10:18 am

Willdebeers wrote:
Mimikool wrote:Nice built ;)

You can use a meter to introduce the exactly amount of fuel. I thinks the propane have to occupy 4% of the mixture.

So build a pipe, which the volume is 4% of the chamber volume, and you put in the meter (the pipe) the same pressure as the final mixture. If you want 10x, you put 10bar of propane before open the ball vavle.

The propan becomes a liquid at 7bar, so you multiply the meter volume by 2 and divide the pressure by 2 ;) to have the same amount of fuel.

Then you insert the air ;)

What's your ignition?


My ignition is a peizo, nothing special. Stunguns & other HV circuits are illegal in the UK, so not much luck there. My spark gap is <1mm so I should be good there.

Even if I had 2 1/4" ball valves connected with a close nipple, it would still not be 4%, so I may need to do a little maths to get the correct mix.


Personally, I would make the meter something substantially more than 4% of the chamber volume. That way, you're not limited by propane's vapor pressure. (even then, you could fill the meter multiple times).

As far as ignition goes, try to find an automotive ignition coil, and rig that up with either a disposable camera or a 12V battery. It's be a shame to see something this well built ignited with a mere piezo (and then you can go to higher mixes).
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Unread postAuthor: Willdebeers » Sun Jul 17, 2011 10:22 am

ramses wrote:
Willdebeers wrote:
Mimikool wrote:Nice built ;)

You can use a meter to introduce the exactly amount of fuel. I thinks the propane have to occupy 4% of the mixture.

So build a pipe, which the volume is 4% of the chamber volume, and you put in the meter (the pipe) the same pressure as the final mixture. If you want 10x, you put 10bar of propane before open the ball vavle.

The propan becomes a liquid at 7bar, so you multiply the meter volume by 2 and divide the pressure by 2 ;) to have the same amount of fuel.

Then you insert the air ;)

What's your ignition?


My ignition is a peizo, nothing special. Stunguns & other HV circuits are illegal in the UK, so not much luck there. My spark gap is <1mm so I should be good there.

Even if I had 2 1/4" ball valves connected with a close nipple, it would still not be 4%, so I may need to do a little maths to get the correct mix.


Personally, I would make the meter something substantially more than 4% of the chamber volume. That way, you're not limited by propane's vapor pressure. (even then, you could fill the meter multiple times).

As far as ignition goes, try to find an automotive ignition coil, and rig that up with either a disposable camera or a 12V battery. It's be a shame to see something this well built ignited with a mere piezo (and then you can go to higher mixes).


That seems like a massive hassle, and the peizo can produce a 3/4" spark as it is. It will probably easily deal with a 10x mix with a 0.5mm spark gap.
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Unread postAuthor: saefroch » Sun Jul 17, 2011 10:45 am

JSR has had piezo ignition up to 28X I think, 10X won't be a problem.
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Unread postAuthor: Willdebeers » Sun Jul 17, 2011 11:42 am

saefroch wrote:JSR has had piezo ignition up to 28X I think, 10X won't be a problem.


JSR made a 28x mix hybrid!?

Was it made out of epoxy :P
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Unread postAuthor: spudamine » Sun Jul 17, 2011 12:44 pm

Stunguns & other HV circuits are illegal in the UK


Stun guns yes, other HV circuits no. I haven't seen the police raiding any Tesla coil conventions yet and they would probably be more interested in what it was attached to :lol:
But yes JSR has proved much higher mixes can be ignited with a piezo so you should be ok (and yes it was actually made from epoxy)
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 17, 2011 12:54 pm

saefroch wrote:JSR has had piezo ignition up to 28X I think, 10X won't be a problem.


With a paper thin spark gap, I could only get 16-17x maximum to ignite with a piezo.

You can buy oven ignitors like this one that run off a 9V DC battery that will be good well above 30x

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JSR made a 28x mix hybrid!?

Was it made out of epoxy


Oh ye of little faith... ;)
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Unread postAuthor: Willdebeers » Sun Jul 17, 2011 1:22 pm

jackssmirkingrevenge wrote:
saefroch wrote:JSR has had piezo ignition up to 28X I think, 10X won't be a problem.


With a paper thin spark gap, I could only get 16-17x maximum to ignite with a piezo.

You can buy oven ignitors like this one that run off a 9V DC battery that will be good well above 30x

Image

JSR made a 28x mix hybrid!?

Was it made out of epoxy


Oh ye of little faith... ;)



You seem to be quite well known for your...ermm... "less successful" projects. ;)

Thanks for the advice. I may pick up one of those igniters, but for now, with low mix tests, a peizo is fine.
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 17, 2011 1:30 pm

Willdebeers wrote:You seem to be quite well known for your...ermm... "less successful" projects. ;)


It's the fact that I tend to post the vast majority of my projects, whether they work or not, that others might at least learn from my failures.
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Unread postAuthor: Willdebeers » Sun Jul 17, 2011 2:10 pm

jackssmirkingrevenge wrote:
Willdebeers wrote:You seem to be quite well known for your...ermm... "less successful" projects. ;)


It's the fact that I tend to post the vast majority of my projects, whether they work or not, that others might at least learn from my failures.


I dare not ask how many litres of epoxy you have used! :shock:

How many projects have you tried? I have seen some of them and they seem very impressive. One question I have is how can you set such complicated structures in epoxy? Some of the valve designs seem ludicrous, yet you still manage to pull it off.
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 17, 2011 2:44 pm

Willdebeers wrote:I dare not ask how many litres of epoxy you have used! :shock:


Since I started messing with epoxy just over 10 years ago, about 15 litres.

How many projects have you tried?


Lots!

I have seen some of them and they seem very impressive. One question I have is how can you set such complicated structures in epoxy? Some of the valve designs seem ludicrous, yet you still manage to pull it off.


Experience, getting a good casting technique, patience, and the willingness to start over if you mess up.

Anyway,times have changed ;)

Back to the subject of this thread, have you considered starting off with syringe metering? It's less complicated to set up than manometric metering and reliable if done right.

From another thread:

[youtube]http://www.youtube.com/watch?v=0nM603eOQU4[/youtube]

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 10mL chamber using butane to say 5x, the calculation is as follows:

3/100 x (10+1.75) x 5 = 1.76mL of butane

Had we not considered the pump dead volume, the result would have been 1.5mL of fuel, an error of 15% which would most likely prevent ignition. If it were a 100mL chamber on the other hand, the error would have been of 1.5%, and likely the mix would have still ignited.

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

(mix number - 1) x 14.7

In the case of our 5x mix, the calculation is as follows:

(5-1) x 14.7 = 59 psi

If your gauge can read bar, simply pressurise to (mix number - 1) bar, so 4 bar in this case.
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Unread postAuthor: Willdebeers » Sun Jul 17, 2011 3:57 pm

jackssmirkingrevenge wrote:
Willdebeers wrote:I dare not ask how many litres of epoxy you have used! :shock:


Since I started messing with epoxy just over 10 years ago, about 15 litres.

How many projects have you tried?


Lots!

I have seen some of them and they seem very impressive. One question I have is how can you set such complicated structures in epoxy? Some of the valve designs seem ludicrous, yet you still manage to pull it off.


Experience, getting a good casting technique, patience, and the willingness to start over if you mess up.

Anyway,times have changed ;)

Back to the subject of this thread, have you considered starting off with syringe metering? It's less complicated to set up than manometric metering and reliable if done right.

From another thread:

[youtube]http://www.youtube.com/watch?v=0nM603eOQU4[/youtube]

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 10mL chamber using butane to say 5x, the calculation is as follows:

3/100 x (10+1.75) x 5 = 1.76mL of butane

Had we not considered the pump dead volume, the result would have been 1.5mL of fuel, an error of 15% which would most likely prevent ignition. If it were a 100mL chamber on the other hand, the error would have been of 1.5%, and likely the mix would have still ignited.

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

(mix number - 1) x 14.7

In the case of our 5x mix, the calculation is as follows:

(5-1) x 14.7 = 59 psi

If your gauge can read bar, simply pressurise to (mix number - 1) bar, so 4 bar in this case.


Thanks for the help :)

I filled the chamber with water to get the size, and it came to ~12cm3.

I was going to use a dual ball valve setup, but syringe metering seems very nice indeed. I happen to have a 5ml syringe, which I was messing around with. I hope to use this at maybe a 50x mix, seeing as it is 7mm thick metal.
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