Deflagration to Detonation Transition. It is what occurs when the normal deflagration of a fuel transits into the detonation of that fuel, or the burning of the fuel above the speed of sound. This produces a very high pressure spike.
It is most likely to happen in high mixes, but certain things can make it more likely to happen even in low mixes, even as low as 1 ATM, (though very, very unlikely unless you have a 50 foot long chamber).
"Run-up time" is the distance inside of a pipe filled with a fuel/air, fuel/oxidizer mix required until the transition occurs. This is the time it takes the fuel burning to accelerate to where DDT occurs. Just so you know, decreasing run-up time = bad.
Run-up time is decreased by a few things...
1.) Pipe diameter: as pipe diameter goes down, the run-up time decreases.
2.) Turbulence: turbulence along the flame front shortens run-up time.
3.) The mix: reactivity in these areas are judged by flame-front cell size. Propane is a stable fuel, relatively compared to stuff like ethylene and acetylene. So, basically, don't use sh** like that.
4.) The mix 2: Obviously, as your mix becomes more compressed or rich in oxygen/fuel, (enriched mixes), the run-up time is decreased.
5.) The mix 3: lean mixes shorten run-up time, because the initial speed of the combustion is increased.
DDT is a real threat in hybrid cannons, but many people forget that it is dangerous any where where you have a fuel/air mixture with sufficient distance to accelerate the combustion. DDT has been recorded to have happened, (but I forgot the link
), in a 1 atm setting in an open situation with natural gas. I believe an oil rig...
EDIT: and onto construction and safety precautions. All pipe and fittings, SHOULD, be SCH 80 PVC with an ASTM rating. Rated for fluid pressure. Don't just trust an NSF rating, get the ASTM rating.
Solvent welding should be done PROPERLY. Use a PROPER sized applicator and proper techniques and wait 24-72 hours for the joints to cure.
Threaded joints are bad. Reduce to a minimum. Also, don't drill and tap any more holes than you have to.
<font>DO NOT BREECH A 4X/4X ATM MIX!!!</font>