Nitrogen oxide emissions analyses in ammonia/hydrogen/air premixed swirling flames

Ammonia/hydrogen fuel blends have gathered interest as a promising solution for the development of a hydrogen economy, with advantages in storage cost or combustion properties compared to pure hydrogen or pure ammonia, respectively. In that pursuit, the present work reports the trends of nitrogen oxide emissions for ammonia/hydrogen blends at atmospheric conditions. NO, NO2 and N2O productions/consumptions are approached in detail in combination with unburnt ammonia. All cases are measured in a turbulent, swirl-stabilised flame configuration across hydrogen fuel fractions from 0% to 25% and equivalence ratios from 0.55 to 1.30. A detailed chemistry analysis was conducted using a chemical reactor network (CRN) employing detailed reaction chemistry. The results show that NO and NO2 emissions peaks around Φ = 0.8, whereas considerable amount of N2O is generated at very lean conditions, Φ ≤ 0.65. Availability of OH radicals and O/H pools in the flames contribute towards fuel NO formation, which in turn produces NO2 and N2O. However, very lean conditions lead to lower temperatures that ensure the survival of N2O. The results identified Φ = 1.05–1.2 as the optimum equivalence ratios for reduced NOX emissions in ammonia/hydrogen blends, with further understanding of the flame chemistry responsible behind these emissions.