Combustion characteristics of premixed ammonia-hydrogen/air swirl flames at elevated pressure

Ammonia (NH3)-hydrogen (H2) blends which are obtainable by NH3 cracking can be an eminent carbon -free fuel. To provide a valuable database for the practical application of cracking -based NH3-H2 fuel, the effects of pressure on the combustion characteristics of premixed NH3-H2(-nitrogen (N2))/air swirl flames are investigated in terms of H2 mole fraction in the NH3-H2 blend and fuel -equivalence ratio. Extinction mechanisms at fuel -lean and rich flames are the same for both normal and elevated pressures, though only the blowoff is observed for elevated pressure. With increasing pressure, fuel -rich limits are generally extended but fuel -lean limits are reduced, NOx emissions decrease and the condition of the maximum NOx emissions moves towards fuel -richer condition. Flame visualization exhibits the shifted main reaction zone upstream, the increased flame wrinkling and the reduced OH and NO intensities with increasing pressure. Dilution effects of N2 at elevated pressure become remarkable compared with those at normal pressure.