The pressure has nothing to do with the energy density. That is in the specific substance itself....basically, yea I know. By your thinking it would not burn if not under more pressure then 200psi.
I am not trying to be difficult as well, I am trying to learn here, I will freely admit if I am in error, and it is real possible that I am, I want the facts.
So if you had hydrogen in an open tank at a no pressure over normal, I am under the understanding that the hydrogen will rise, and the gas can be captured and used as a fuel.
I saw a video, hay it is on the interwebs so it must be true right? (part of what I am trying to learn fact from fiction) and he had one of those stainless steel hydrogen generators stuck in water, put power to it, and the water starts to bubble, we did this 40 years ago in science class in high school. This guy however had some kind of collector that would vent the hydrogen gas into an engine with (I guess called a mixer) used for LP with some changes to it he did not go into, and the engine ran. I understand this "mixer" thingy to be basically a carb for LP.
In my mind in Mrs. Blake in 8th grade science could make it go woosh with just a positive and neg cables run to it (I don't remember the voltage she used) that woosh sure seemed like gasoline vapor and that is really what you are trying to do with normal gas to make it burn, and any idiot (ME) that has ever been stupid enough to start a fire with gas knows it is the vapor that is the real worry.
We can take this to another thread if you want, I really do want to learn about this.
Here is the link to the Jay Leno video I was talking about.....time sure does fly, this was 14 years ago. I am sure a thing or two has been learned from the tape of that video.