Pang -
There is no such thing as a flame that burns up CO2. CO2 is the
most 'burnt up' form that a carbon-based molecule can end up in. The
scientific way of saying this is that it is the most 'oxidized' form
possible. Flames work by converting molecules with carbon in them into
CO2 and other molecules.
If it doesn't have enough oxygen, a flame might not be able to turn
the molecule all the way into CO2 - sometimes it produces what we call
'intermediates', or molecules that are more burnt up than they used to
be, but less burnt up than CO2 (like the molecules in soot). Luminous
flames are less efficient than non-luminous ones, so they are more
likely to produce these intermediates. But no flame can burn up CO2.
-Tamara
(published on 10/22/2007)