There is nothing wrong with it as a fuel. My knee-jerk opinion is that it would be better off in larger motors, and that because the flame speed is low. I'm searching for a table, but generally I would compare autoignition temperatures, flame speeds, stoichiometric mix. Yes, it does have a high energy density.
The tiniest motors need hydrogen or acetylene because they run it at such a high frequency, and so need A high flame speed.
In bigger motors a fast flame speed my just lead to detonation.