Come on guys, don't assume he's an idiot immediately. It takes a special kind of stupid to research the topic and leave thinking that air/propane at 1X might rupture SCH40 steel. He's just taking a rather difficult approach to the problem. The steel pipe probably isn't sealed at all, and he probably unthreads the setup and checks the remaining gases after he pushes the ignition to see if combustion occurred. It's easy enough to tell whether a gas mix supports combustion with a match or something similar.
Achieving ignition under certain conditions is rather tricky, skyjive, and you've got one here - small diameter pipe, with ignition at one end and no supplementary oxidizer. The limits of combustion here are quite narrow, and they're obviously not being reached at the sparkplug. My first guess would be that the mix is lean near the ignition.
I'd suggest a shorter, larger diameter main pipe. Using clear tube, if possible, will obviously make the testing easier as you won't need to unthread and check the remaining gases after each test. Also, recheck your meter calculations, just to be sure.
It does not explode.
In the interests of accuracy, it should be noted that "explode" does not denote a detonation, or even a deflagration. In fact, the meaning of the word is so vague as to make it almost entirely useless. A balloon "explodes" when you stomp on it, a cloud of poorly mixed air/propane "explodes" when it is ignited (despite possibly taking a second or more to burn fully), and a barrel of ANFO "explodes" when initiated with a few kilos of secondary. When using the word "explode", you make no distinction whatsoever.
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
Guess it didn't work.
