Stability enhancement of liquid ammonia swirl combustion through nozzle geometry optimization

AbstractThe application of liquid ammonia (LNH3[jls-end-space/]) in gas turbine combustion is severely restricted by poor flame stability. In this study, the causes of this poor flame stability were identified by comparing LNH3 and gaseous ammonia (GNH3[jls-end-space/]) combustion, and two optimized nozzles, namely a deflector-plate nozzle (LPN) and a multi-hole nozzle (LMN), were developed. OH-PLIF/Mie scattering, TDLAS gas analysis, and two-phase LES were used to investigate the combustion, evaporation, and mixing characteristics. The results show that reducing the axial momentum of the LNH3 spray enhances mixing and decreases the aera of low-temperature zone, which is critical for improving flame stability. Compared with the single-hole nozzle (LSN), the LPN reduced spray axial momentum to 0.508–0.55 and decreased the in-chamber droplet area by 78%–90%. The LPN19.5 extended the rich blow-off limit to (Formula presented) and lowered unburned NH3 emissions to 489 ppm at (Formula presented). The LMN showed the best overall performance, reducing spray axial momentum to 0.1146 and the in-chamber droplet area by 99.4%, extending the combustion limits to (Formula presented) (rich) and 0.617 (lean), and keeping unburned NH3 below 33 ppm over (Formula presented) .Novelty and significance statementThe novelty of this work lies in its systematic elucidation of the poor stability mechanisms in liquid ammonia swirl spray combustion and the significant enhancement of flame stability through nozzle design optimization. This study is significant because it is the first to clarify the underlying causes of liquid ammonia flame poor stability through comparative analysis of gaseous and liquid ammonia spray combustion, and to address these challenges through the pioneering development of deflector-plate (LPN) and multi-hole (LMN) nozzles. The optimized nozzle geometries ultimately enable efficient and stable combustion of pure liquid ammonia in a single-stage combustor. These results provide practical design guidelines for liquid ammonia nozzles, offering a viable pathway toward high-efficiency, stable pure ammonia combustion in gas turbine systems.