Carbon Dioxide is a pollutinggas which mainly occurs as a waste product in certain petrochemical or material refinement processes. Although it is used as a coolant in the ZIRNOX, which uses up to 16000 mB of it.
Currently, the only use for CO2 is as a coolant for the aforementioned ZIRNOX. More is not necessarily better, and some trial and error will be needed on the part of the player to determine the ideal amount for a particular fuel load.