Very little of the released carbon is actually consumed in the combustion reaction because flame temperature seldom reaches the vaporization point of carbon. Most of it combines with oxygen to form CO2 and passes out the vent. Carbon which cools before it can combine with oxygen to form CO2 passes out the vent as visible smoke. The intense yellow color of an oil flame is largely caused by incandescent carbon particles. Complete Combustion is achieved when all the fuel is burned using the minimal amount of air above the theoretical amount of air needed to burn the fuel.
Complete combustion is always our goal.
With complete combustion, the fuel is burned at the highest combustion efficiency with low pollution. Incomplete Combustion occurs when all the fuel is not burned, which results in the formation of soot and smoke.