Pedal To The Metal
I read about a fascinating alternate fuel source - metal powder, in this case, iron powder.
Since washing the FeO in hydrogen restores it to a useable state, I suppose a complete tank of iron dust wouldn't be necessary. If one knows the time to wash the oxide in hydrogen to restore it and how many cycles the engine makes in that time, all you'd have to do is carry enough iron dust, maybe 10% extra for variable factors, to run the engine long enough to have the earliest used iron cleaned and returned to the engine.
Then, all you'd need to carry would be the necessary hydrogen - a lot lighter than iron - to do the washing.
Since the exhaust is water - the same as a hydrogen fuel cell - you could dump it or condense it from vapor to liquid to use back at home. It should be pure water, no contaminents, so you could store it for consumption or just to water the yard.