The characteristics of NOx reduction in O2/CO2 combustion were investigated experimentally and numerically. Experiments showed that the exhaust CO concentration in O2/CO2 combustion was almost twice as much as that in air combustion. This was because high CO2 concentration enhanced the reaction (CO2 + H → CO + OH). A mass of OH radicals led to the oxidation of NH3 and HCN. The sum of the nitrogen-species in O2/CO2 combustion was less than that in air combustion. It meant that NO formation suppression effect was high in O2/CO2 combustion. N2 conversion ratio became an effective guide to show NO formation suppression effect quantitatively. Calculations showed that N2 conversion ratio was high in O2/CO2 combustion and the unique NO reduction scheme caused by high CO2 concentration. This scheme proceeded under high CO and OH concentration. It was shown that O2/CO2 combustion was suited for reducing nitrogen-oxide due to the unique NO reduction scheme.

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