Ammonia/Hydrogen and Cracked Ammonia Combustion

Ammonia is a promising energy carrier for energy system decarbonization, although several drawbacks affect its combustion process. Coupling moderate or intense low-oxygen dilution (MILD) combustion with the use of high reactivity fuels allows to improve NH3combustion. In particular, H2addition may be a feasible strategy, considering the high proportion of H2achievable by NH3partial cracking. The present study focuses on MILD combustion effectiveness in ensuring high stability and low-NOxemissions for NH3/H2blends. Influence of both equivalence ratio and H2addition was experimentally investigated in a cyclonic reactor. Furthermore, the results were directly compared with those obtained with cracked NH3mixtures (NH3/H2/N2). Results for NH3/H2blends strengthen the fuel flexibility of the cyclonic reactor, which allows total conversion of the fuel mixtures by ensuring operating temperatures always lower than 1400 K, independently of the equivalence ratio and the fuel blend composition. In particular, H2addition increases NH3reactivity, whereas increasing NOxemissions with respect to pure ammonia. Instead, for pure H2and pure NH3, they always stay lower than 40 and 100 ppm, respectively. For cracked NH3mixtures, the fuel dilution content by N2does not affect the NH3/H2combustion behavior under MILD conditions. Instead, for 100% NH3cracking (75%H2-25%N2mixture), H2dilution by N2entails a more uniform reaction zone than not diluted H2case, further limiting NOxformation by avoiding the occurrence of hot-spot regions within the reactor.