Can you really build an engine that runs on air?

Question

HOW?

Answer 1

It can't run on air, because air does not have any significant carbon or hydrogen content. Air is not a fuel. However, all engines use air in the combustion process, together with some other fuel.

Answer 2

AIR? if you mean Hydrogen, then the answer is yes.

Answer 3

you can make one that runs from compressed air, if that's what you mean.

Plain old uncompressed air? no

Answer 4

Is the question can someone build an engine OR can an engine be built that is fuelled by air? The theory exists that an engine can be fuelled with  hydrogen. The oxygen  is a catalyst for combustion.