# What can I use as a fuel for an engine with carbon dioxide as the oxidizer?

On Mars carbon dioxide is abundant. It is plausible to utilize a fuel in an engine that can use carbon dioxide as an oxidizer? I know this is a strange inquiry, but could a engine be made to use $$\ce{CO2}$$ in the martian atmosphere the same way most engines consume $$\ce{O2}$$ on Earth?

Usually when we say something "burns", it's being oxidized. In the case of carbon dioxide only the oxygen can be oxidized, by displacing it as the element; that requires fluorine or a sufficiently powerful fluorinating agent.

Carbon dioxide supports combustion, acting as the oxidizer instead of being oxidized, with some active metals such as magnesium. Thus

$\ce{2 Mg + CO_2 -> 2 MgO + C}$

Such reactivity is why special reagents are needed to extinguish burning active metals.