That’s what I was thinking. Replace the oxygen with whatever is on the atmosphere and add oxidizer.
If I could, I might be able to do a little science experiment regarding this.
Where we use a mini turbojet engine used by hobby aircraft modellers, and duct hydrogen/methane into the intake, and feed oxidiser into the fuel feed, of course we have optimize the engine fuel control software for this scenario.
Jet engines usually burn "air rich", otherwise the excess unburnt fuel would coke up the innards. So you gotta "flip" the programming on its head, easier said than done, as different oxidisers have different stoichiometric ratios (you might find this out by referring to the US Army Propellant Handbook, however most of them cater to solid or liquid rocket engines, not gas-gas) you have to consider to find the perfect mix.
The hardware I'll need for this experiment will be very expensive, so maybe it's best for NASA to try.