[Objective

]

Ammonia(NH

3

)

as an economically viable zero-carbon fuel and an attractive hydrogen carrier

can effectively broaden the flammability limits and improve emission characteristics when blended with hydrogen(H

2

). However

in practical high-pressure combustion devices such as gas turbines

the nitric oxide(NO) formation characteristics of NH

3

-H

2

flames exhibit significant differences compared with those under atmospheric pressure conditions. In particular

the compression of the reaction zone at elevated pressure makes it difficult to directly compare combustion characteristics in physical space. [Methods

]

To address this issue

this study employs ANSYS

Chemkin to conduct numerical simulations of high-pressure NH

3

-H

2

counterflow diffusion flames. Based on mixture fraction space

the effects of pressure(0.1 and 1.0 MPa) and the NH

3

blending ratio(0 to 60%) on flame structure

NO mole fraction

and NO formation characteristics are investigated. The adopted flame model and kinetic mechanism were first validated against available experimental data

and the key reactions controlling NO formation were further identified based on the rate of production(ROP) analysis. [Results

]

The results indicate that mixture fraction can effectively characterize the structure and combustion characteristics of NH

3

-H

2

diffusion flames. Compared with physical space

the temperature distributions of NH

3

-H

2

flames under different pressure conditions exhibit good consistency in mixture fraction space. As the NH

3

blending ratio increases

the peak temperature exhibits a monotonically decreasing trend

whereas increasing pressure significantly raises the peak temperature and compresses the reaction zone. NH

3

blending alters the primary NO formation region

shifting it from thermalNO dominance in pure H

2

flames to fuel-NO dominance in flames with NH

3

blending ratios larger than 20%. At 0.1 MPa

the NO peak increases monotonically with the NH

3

blending ratio

and reactions R39(N+OH=NO+H) and R179(HNO+H=NO+H

2

) dominate NO formation. At 1.0 MPa

the NO peak exhibits a non-monotonic trend

first decreasing and then increasing. The contribution of reaction R180(HNO+ OH=NO+H_2O) to NO formation is enhanced. The reduction effect of NH

3

pyrolysis products on NO is significantly promoted

whereas the mutual conversion processes among NO

x

species have a relatively limited impact on NO formation. [Conclusion

]

This study reveals the effects of pressure and NH

3

blending ratio on the structure and NO formation characteristics of high

-pressure NH

3

-H

2

counterflow diffusion flames

and identifies the dominant pathways and key reactions involved in NO formation. These findings can provide theoretical guidance for the application and emission control of NH

3

-H

2

fuels in high-pressure combustion devices.