Ignition?

[SNDM]

First of all let me introduce my project.

It is a low power copper hybrid.
(Low power because I have no idea to the strength of the copper. It is kitemarked, but other than that I don'tknow of any other ratings on it.
Looks pretty thin too.)

I need a way of igniting the Hydrogen/Oxygen mix.
I have basically an end cap in which to install the system.
It is 22mm dia size.

I was wondering what easy designs people used, which kept their launcher strong.

[SpudFarm]

i would be worried about DDT in a thin chamber like that..

and if it is short so DDT is no danger copper can take 4x no problem..

spark plug is the way to go

[MaxuS the 2nd]

The burst pressure of copper is over 1000psi.

I suggest you drill a hole in the end cap and using a bulkhead nut, clamp a spark plug into it.
If your chamber is too long though, it may cause DDT.

Edit: FFS spudfarm, that's the second post you've beaten me to in 30 seconds. I'm going to retire.

[SpudFarm]

haha:D i am evil

[DYI]

Firstly, I think you should immediately scrap the idea of using oxy/hydrogen in such a low diameter pipe. Copper tube failures are relatively benign, even if you set off high explosives in them, but you don't want to waste time and money building a launcher that might explode on the first shot.

Use a larger diameter copper pipe to start with, at least 50mm or so. Don't make it any more than 4 times as long as it is wide. Then, you can probably go up to at least 8x (the nX system means very little with hydrogen, as the fuel takes up so much volume).

For sparkplugs, most of my designs are some variation of two copper rods passing through a 1/2" to 1/4" bushing (threads give the epoxy better grip) filled with JBweld. These designs have only ever failed when exposed to pressure of over 5kpsi and a 2km/s shockwave, so they should be good for any reasonable low mix hybrid.

[SNDM]

The largest copper pipe I can get access to is 28mm.
Im having problems sourcing a union.
Im not willing to use a web order, so Im picking apart my local B&Q.

Are compression fittings alrights for this application?

[MaxuS the 2nd]

Im not willing to use a web order

Then you will not save much money.
B&Q, are you from the Uk?

[SNDM]

That I am.

The Far North, Scotland, as highway signs would tell me.

[mark.f]

Why not go with steel pipe? It'll be cheaper than copper of the same diameter (especially going into the 2" diameter range as DYI suggested), and you can install a spark plug by simply drilling a 1/2" hole and tapping with a 14 x 1.25 metric tap.

[MaxuS the 2nd]

That I am.

The Far North, Scotland, as highway signs would tell me.

Same, except I'm from the South East of England.