OK.  I made a new version of my fusion cannon that uses CO2 as the source gas  its harder to ignite and i needed to supply 2x as much CO2 as was needed for HYGN.  however the resulting reaction produces a great deal of HOT OXYG under high pressure.  very nice for the cannon or a rocket engine.  you can inject nitro or gas in near the nozzle and get a very nice flame thrower/rocket engine effect.  id:1717000

Build a titanium frame around your fusion chamber.  Otherwise you are trying to pressurize the entire TPT environment, and will need lots of pumps (plus all that runaway pressure makes things messy).  Cray usage allows you to set tmp (range), heat and type of material to fuse.  All that is left is to provide gravity and pressure with prolly an auxilary heater to start up, sandwichlizard did a good save with lots of different heaters. Simplest for this use is prolly ARAY with temp set to max; heating a pixel wide strip of vacuum with BRAY. This in turn heats your fusion chamber.  Again, see SandwichLizard's heater builds or you will find an example in the last save I include below. Also remember that with CRAY the fusable substance can also contribute heat and can be injected at proper temp greatly simplifying the whole procedure.

Here are some fusion builds: 

This is small O2 fusion one step up from CO2. Change the Cray's ctype to CO2 and it will fuse as setup.

This is hydrogen fusion with four pixel elements.

This is better build of same idea; not as small.

This is how I use a (two really) very fast O2 fusion generator to make lots of hot metal to hurl at bunkers.

*** Everything I post is free to copy (if it's deemed worthy).