Hydrogen as fuel

[JABN]

Would it be a good idea to use hydrogen as a fuel for a cannon and if so like what percentage of hydrogen should there be in the CC.

[saefroch]

Stoichiometry gives you an estimate of a 2:1 ratio of Hydrogen:Oxygen. Given that air is ~20% oxygen, that's a 2:5 Hydrogen:Air ratio, so your chamber is about 28.5% hydrogen, as opposed to 4.2% for propane. I believe there has also been some modeling done with hydrogen as compared to propane, using a program called Gaseq, which have shown using hydrogen as a fuel will be less effective (less expansion, I assume) than propane at atmospheric pressure.

So no, there is no reason to use hydrogen in an atmospheric pressure combustion.

With even just one year of high-school chemistry education, you can produce the numbers I just did.