Abstract
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 NH(3) combustion. In particular, H(2) addition may be a feasible strategy, considering the high proportion of H(2) achievable by NH(3) partial cracking. The present study focuses on MILD combustion effectiveness in ensuring high stability and low-NO (x) emissions for NH(3)/H(2) blends. Influence of both equivalence ratio and H(2) addition was experimentally investigated in a cyclonic reactor. Furthermore, the results were directly compared with those obtained with cracked NH(3) mixtures (NH(3)/H(2)/N(2)). Results for NH(3)/H(2) blends 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, H(2) addition increases NH(3) reactivity, whereas increasing NO (x) emissions with respect to pure ammonia. Instead, for pure H(2) and pure NH(3), they always stay lower than 40 and 100 ppm, respectively. For cracked NH(3) mixtures, the fuel dilution content by N(2) does not affect the NH(3)/H(2) combustion behavior under MILD conditions. Instead, for 100% NH(3) cracking (75%H(2)-25%N(2) mixture), H(2) dilution by N(2) entails a more uniform reaction zone than not diluted H(2) case, further limiting NO (x) formation by avoiding the occurrence of hot-spot regions within the reactor.