NO formation mechanism of CH4/NH3 jet flames in hot co-flow under MILD-oxy condition: Effects of co-flow CO2 and H2O

•Revealing the chemical effects of CO2 and H2O on homogeneous fuel-NO mechanism.•CO2 favors the establishment of MILD regime by reducing the overall oxidation rate.•NO formation is both enhanced with the increasing contents of CO2 and H2O.•CO2 addition mainly facilitates the generation of NO via HNO as the intermediate.•Increasing H2O level evidently strengthens the route NH3 → NH2 → NH → N → NO.