An experimental and numerical investigation of a liquid ammonia jet flame: spray characteristics close to nozzle and flame structure

Liquid ammonia combustion has become a focal point in current ammonia combustion research due to its potential to simplify fuel supply systems, reduce costs, and improve the responsiveness of combustion systems. In this study, the spray characteristics of liquid ammonia close to the nozzle and jet flame structure are experimentally and numerically investigated. The spray characteristics of liquid ammonia generated using an ammonia piloted jet spray burner (AJSB) are measured using Particle/Droplet Image Analysis (PDIA). The liquid ammonia jet flame structure is further analyzed using a quasi-carrier-phase Direct Numerical Simulation (quasi-DNS) coupled with a detailed chemistry under the Euler-Lagrangian framework. The experimental results indicate that the liquid ammonia undergoes flash boiling inside the injection tube, with only 22.8% of the ammonia remaining in the liquid state after injection, and the atomized droplets have an average diameter of less than 40 μm. On the other hand, the quasi-DNS results show that flash evaporation leads to a low axial flame temperature, with droplets confined to the low-temperature region and almost completely evaporating before reaching the flame front. In addition, the results indicate that the expansion of the reaction zone in the liquid ammonia jet flame is a process that develops spatially from upstream to downstream while being influenced by the interactions between local eddies and the flame. This behavior is consistent with the findings reported in gaseous ammonia jet flames, a similarity attributed to the characteristics of liquid ammonia flash evaporation, resulting in combustion characteristics similar to those of gaseous ammonia.