Numerical study of hydrogen peroxide enhancement of ammonia premixed flames

NH₃ is considered a promising alternative for hydrocarbon-based fuels. However, NH₃/air combustion has many challenges, including a high ignition temperature and low flame speed. Hydrogen peroxide can be used to overcome these defects. The effects of hydrogen peroxide on the NH₃/air premixed flames are numerically investigated using a detailed chemical mechanism. When using hydrogen peroxide to replace partial air, the laminar burning velocity and adiabatic flame temperature are substantially increased. For higher replacement of hydrogen peroxide, the laminar burning velocity is dominated by hydrogen peroxide reactions related to OH. In addition, addition of hydrogen peroxide increases the species concentration and enhances reaction rates. The dominant reactions for species reaction rates are shifted, especially for OH and H₂O. H₂O is mainly formed from the reaction of hydrogen peroxide attacked with radical OH after the amount of added hydrogen peroxide exceeds 40%. As for NO emissions, it also increases due to the presence of NH₃ and the higher flame temperature. Since hydrogen peroxide can substantially increase the combustion speed of NH₃, thereby extending the flammability limit, it is feasible to control NO emissions by adjusting the replacement percentage of hydrogen peroxide and operating at a lower equivalence ratio.