Numerical Study on the Premixed Oxygen-Enriched Ammonia Combustion

In recent years, ammonia attracts much attention from researchers as a carbon-free energy carrier, but low reactivity hinders the direct use of ammonia in combustion applications. In this study, several essential combustion properties were numerically studied to explore the possibility of using oxygen enrichment to enhance ammonia combustion. Fuel lean and rich oxygen-enriched ammonia flame was simulated by planar flame and one-dimensional spherical flame under various oxygen fractions. Results show that increasing oxygen content substantially increases the laminar burning velocity and mixture heating value but decreases the burned gas Markstein length and combustion efficiency. NO is the major NOx emission, which rises with oxygen content for rich combustion but nonmonotonically changes for lean combustion due to the start-up of NO post-reduction at high temperature. The chemical effect of N-2 possesses negligible influences on most of the flame properties, except for weakening the NO post-reduction in the burned gas. Competition between the increase in flame temperature and the decrease in N-2 content leads to the maximum chemical effect of N-2 occurring at the oxygen fraction of 0.6. In summary, oxygen enrichment can be an effective option to solve the problems impeding ammonia fuelization.