Astrophysicist Ethan Siegel notes that the combustion would require some oxygen to oxidize the reactants. Moreover, most of the energy produced would turn into heat, not momentum, he says. So the acceleration would be slower than predicted.

Incidentally, NASA has been well aware of the explosive power of flatus for some time now. Back in 1969, researchers at the University of California – Berkeley sought ways to minimize the fire hazard presented by farting onboard spacecraft by feeding subjects diets designed to minimize the output of bodily gases.