SpudFiles

ok so i was thinking about building a combustion launcher from some 3/4 pvc and a 2 liter soda bottle. I just want it to shoot paintballs at a fairly low velocity (below 300 fps). I have all my plans and shit worked out and i was wondering what you guys would think about me trying direct injection on this bad boy?

I would do the crack lighter trick to amp up the fuel injection so it wouldn't take forever

What exactly do you mean by "direct injection"?

I have all my plans and crap worked out and i was wondering what you guys would think about me trying direct injection on this bad boy?

I would do the crack lighter trick to amp up the fuel injection so it wouldn't take forever

WTF does this mean

I take it a "Crack lighter" is one of those jet cigarette lighters?

Edit: Drugs are bad mmmmk... Don't take drugs mmmmmmmkkk.

like a barb is screwed into the chamber and the hose is run off to the fuel source (lighter in this case) and when you push the button it pumps the fuel into the chamber instead of having to spray shit into the chamber by unscrewing everything

How does one propose to implement the exchange of dead air for new air?

you need to greatly elaborate on your question and description

a ball valve between the barrel and chamber that opens to the air so you can vent the chamber. dude I'm not retarded i know that if you don't vent then any unburned gas will make the fuel mix too rich and it won't ignite

"direct injection" is the best way to ensure an optimal fuel mix. Of course with a vent of some sort

F.E.A.R._Sniper wrote:a ball valve between the barrel and chamber that opens to the air so you can vent the chamber. dude I'm not retarded i know that if you don't vent then any unburned gas will make the fuel mix too rich and it won't ignite

I did not call you retarded That aside are you sure that one ball valve will suffice? Maybe two would be better as you could provide an air flow to really make sure that you have fresh air in the chamber. That said if the barrel extended into the chamber i suppose one valve would be enough.

yeah the barrel will go back into the chamber a little bit.

it is actually built like this.

take the bottle and lay it on its side. then stick a short piece of 3/4 down the neck of the bottle and make JSR happy and epoxy it into the neck. on the other end put a tee on there. on the direct opposite side of the chamber place a small section of 3/4 with the ball valve on the other end. from the top of the tee you have enough 3/4 to clear the chamber and then you mount a 90 on there to make the barrel run paralel (sp?) with the chamber. then fire it off some!!!

People think that i'm weird when i "suck" on my cannons, i think you may fall into that catagory! What? it's the best way to ensure a good fuel load!

into the "I suck on my cannons" category?

"What? it's the best way to ensure a good fuel load!" Thats what the fine print said in Novacastrian's post if you didnt read it.

Yes, direct injection from a butane lighter will work fine. Just need a piece of hose with a suitable ID to fit onto the nozzle of the lighter. I've had good luck using the insulation stripped off a piece of 20G wire.
(from here)
You can just drill a small hole in the chamber and glue the end of the hose into it. Doesn't have to be all that strong since the force on the junction is going to be pretty small.

You don't need a valve between the chamber and barrel. You can just inject fuel after the ammo is loaded.

Venting will be a PITA. If you have a compressor, or a can of compressed air, you can use that to flush out the chamber between shots by pumping air in through the muzzle. You could just stomp on the bottle a few times to exchange the combustion products for fresh air but that will weaken the bottle pretty quickly.

Might want to put a few packing peanuts in the chamber so you can shake the chamber to get the fuel and air to mix.

This method of fueling is very sensitive to the ambient temperature. The pressure in a butane lighter, and hence the flow rate, is very sensitive to temperature. At 80F the lighter is pressurized to about 2.5 ATM, at 40F it is only about 1.2 ATM.