Visualization of liquid ammonia spray using 2p-SLIPI and comparison of liquid ammonia spray and gaseous ammonia combustion in a swirl combustor at atmospheric pressure

Ammonia fuel is expected to contribute not only to the decarbonization of society but also the stabilization of the global energy situation. Liquid ammonia (LNH3) spray combustion is an option for realizing ammonia-fueled gas turbines. However, the spray and combustion characteristics of LNH3 are vastly uncertain. Therefore, the objectives of this study were to clarify the structure of a LNH3 spray and characterize its spray combustion by comparing it with that of gaseous ammonia (GNH3). The spray structure of LNH3 injected from a pressure-swirl nozzle was examined and compared with that of water using high-speed backlight imaging and two-phase structured laser illumination planar imaging (2p-SLIPI) under non-reacting conditions. The LNH3 spray did not form a hollow cone shape, and its shape varied with the injection temperature. The flame stability limits and product gas characteristics of the LNH3 spray and GNH3 combustion were measured and compared in the same combustor under the same conditions at atmospheric pressure for the first time. Mainly three noteworthy results were clarified: the maximum value of NO of pure LNH3/air flames was 2300 ppm less than that of the pure GNH3/air flames; the optimum primary equivalence ratio for the simultaneous reduction of NO and unburned NH3 in pure LNH3/air flames was less than that in the pure GNH3/air flames; the rich-lean two-stage combustion proposed for GNH3 combustion was also effective for LNH3 spray combustion.