Radiative characteristics of premixed ammonia-hydrogen and cracked ammonia swirling flames

• This study finds that radiation from ammonia-blend flames is strongest at Φ = 0.9, with changes being more gradual on the fuel-rich side than the lean side. • Most of the radiation in the combustor comes from H 2 O present in the post-flame zone, rather than from the flame itself. • This study provides the first experimental results that a form of radiative attenuation, likely including the reabsorption of radiation by H 2 O, is active near Φ = 0.9. • The radiative heat flux from ammonia-blend fuels is quantified to be about 25% lower than that of conventional methane fuel. Renewably produced ammonia does not emit CO 2 with combustion. Therefore, numerous studies have been conducted in recent years to utilise ammonia as a carbon free fuel. However, there is limited previous knowledge regarding the radiation characteristics of ammonia blend combustion. In this study, radiation characteristics are investigated for 15 kW premixed swirling flames of NH 3 /H 2 (70/30) and 20% cracked NH 3 , which have been frequent targets of recent research, with equivalence ratios varying from 0.6 ≤ Φ ≤ 1.4. Specifically, water radiation (wavelength 2.7 μm), which is the main radiation source, is measured using an infrared spectrometer. Additionally, radiation emission and absorption in the combustor are evaluated theoretically using H 2 O exhaust gas concentrations and temperature measurement data. The results suggest that radiation changes due to equivalence ratio variations are gradual on the rich side, showing different trends compared to the lean side. Furthermore, radiation attenuation in the combustor become active around Φ = 0.9. This suggests that when considering radiation in ammonia blend combustion, not only the blend composition but also equivalence ratio conditions must be carefully considered. In addition, radiative heat fluxes were analysed for three blends (NH 3 /H 2 , pure NH 3 , and cracked NH 3 ) at Φ = 1.0, suggesting no significant differences in radiative heat flux among these blends. These research findings provide valuable insights for future combustor designs using ammonia blend fuels.