High levels of oxygen can cause otherwise inflammable materials to spontaneously ignite.
CO2 chokes (retards) the flame in relatively small amounts , the two together would ???
There would need to be some happy medium
In effect you are building a rocket or welder the two gases are moderately expensive and onboard production would be $$$ and heavy, likely power intensive as welll.
That said because people are considered too incompetent to fill a water bottle on a car engineers are working on recovering water from exhaust to direct inject at various points during combustion to improve fuel economy and emissions.
https://journals.sagepub.com/doi/abs...68087420933124
https://www.greencarcongress.com/201...-20101015.html