How to fuel a hybrid with a shock pump

[daccel]

This is my attempt to encourage more small hybrid development!

See the prototype thread for background discussion.

Cost: Shock pump - $15, butane torch - $10, misc tubes you likely have on hand - $0, 25x hybrid fuel source - priceless 8).

Assuming your shock pump is a floating o-ring type like this one, then we need to direct the fuel/air from the torch in to the top of the pump at the rod guide.

To do this, drill a hole as indicated in the diagram. Then glue a rubber washer that fits snugly on the rod, onto the rod guide. Apply a bit of oil to the rod to make for easy pumping and prevent the washer from pulling off from friction.

Replace the handle with a shorter one that doesn't come down over the body of the pump.

Drill holes as indicated in the two reservoir tubes. Glue all these tubes together using the small ones to connect them.

Crimp the top tube to fit the plastic hose clip, or more logically find a tube that fits.

Tape the torch tip to the top (just realized it's bottom in the labeled diagram) tube and secure everything in place with abundant use of electrical tape, or your more professional method of choice.

The nice thing with this is that while you need to make things airtight, they don't need to hold any pressure. All the pressurized action happens in the pre-built pump and downstream.

So, anyone have any pneumatic piston cannons or pen guns they want to insert a spark gap into?

DISCLAIMER: This has the potential to easily reach very high mixes. Know your pressure ratings.

[jonnyboy]

Well I have to say I don't understand the assembly at all.

How did you figure out 25x?

[daccel]

Fair enough, my explanations can be lacking at times.

Here are a few intermediate pictures, hopefully they help.

Do you get the basic things you're trying to do here, though - create a U shaped path for fuel/air mixture with an outlet to the pump in the middle, and a sliding seal on the pump rod to divert the intake to the U?

Let me know if you have any specific questions.

25x is based on the pressure the pump can reach and the mix calculator in HGDT. And that's slightly conservative.

[SpudBlaster15]

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[psycix]

How are you so sure that the amount of fuel injected is exactly the right amount?

[daccel]

Spudblaster, yes that is how it works.

I was initially concerned about the danger of shock heating too, but after some discussion here, I thought I would go ahead.

In fact, to keep my conscience clear for when someone else makes one, I just now tried slamming the pump closed as hard and as fast as I could, and I'm still here typing this. I'm no elite athlete, but I think the risk is minimal. That being said, perhaps don't pump with the handle pointed at your face.

psycix, I have no idea what percent of butane it is mixing at. But I have yet to have the mix not ignite with this system. My understanding of butane and propane was that they only ignited within a fairly narrow range, so it must be close. I don't know how a lean or rich mix right on the margins of combustibility effects burn rate or peak pressure, but I can't imagine it completely defeats the power of hybrids.

I don't claim this to be the ultimate fueling method, and a cannon probably won't be quite as efficient using it. But since fueling challenges seem to be a stumbling block to people entering the hybrid field, I thought this would help.

Here is a video of two consecutive tests in a sealed chamber. The flash you see is through the clear epoxy used to hold the spark gap in. I don't have a cannon to demonstrate with, because I am limited to my apartment at the moment, and I don't think my neighbours would be amused. Hopefully getting a truck soon though, and can head out to some remote testing grounds!

[youtube][/youtube]

[daccel]

Here is an alternative. I ran out of butane, so decided to try my propane torch.

The same idea applies - fill reservoir with a/f and divert to pump intake.

Takes a few minutes to find the sweet spot in terms of flow where it is mixing at the right %, but then seems to do so reliably.

Edit: I had some trouble with the washer that seals the rod coming unglued and also not sealing well enough because it wasn't a tight enough fit. So this would be an area to double check for future reference. Replaced and now it's working again.

[Lockednloaded]

I know, I know, don't kick up dead topics, but I'm really interested in this setup...

I have figured out it works with a venturi system to get a proper fuel mix, but how do you calculate the mix number?

[jackssmirkingrevenge]

Fascinating, I had completely missed this, though this was well before I caught the hybrid bug

From what I gather the mix number is simply determined by the pressure to which you pump the chamber, but the fact that a correct fuel concentration is being achieved seems more by accident than design.

I think the syringe method is simpler and more accurate for single shots, but if you're looking to make a pump action hybrid with on board fuel supply, this might be just the ticket!

[jackssmirkingrevenge]

edit: retrospective double post

[Lockednloaded]

The syringe method is much more accurate, but this would be perfect for shortening time between firing. I think the ghetto venturi device could be replaced with a standard propane torch head, correct?

[jackssmirkingrevenge]

I think the ghetto venturi device could be replaced with a standard propane torch head, correct?

The basic idea is similar to this one I had played with for the hybrid cartridge, but in daccel's case it's a multistroke



As long as you're feeding a 1x mix (concentration based on pump and chamber volume) into the pump cylinder, you'll always have the correct fuel concentration no matter what pressure you chose to pump to.

[Lockednloaded]

I think I'll try the Utube venture setup because I don't have a propane torch head atm, I have this exact same shock pump, and the best this is the mode doesnt damage the pump enough to make it unusable. I'll need an ignitor to test this, I already have a small burst disk hybrid as a testing model, but my ignitor dyed on me, so it may be a few days before I can get a new one

[Crna Legija]

do you need the U?, you can just use a hose right

[Lockednloaded]

The U is a simple venturi system, which is the heart of this system.