The two-phase characteristics of liquid ammonia jet spray flame in a hot and low-oxygen coflow

The application of liquid ammonia (LNH₃) combustion is receiving increasing attention. The high latent heat of vaporization and low flame speed of LNH₃ pose challenges for its application as a fuel. Burning LNH₃ in a hot and low-oxygen environment is a potential method to efficiently stabilize the flame. In this study, to investigate the fundamental behaviors of LNH₃ flames, a jet spray flame is studied using an ammonia piloted jet spray burner (AJSB). The flame structure and droplet–flame interaction are investigated for the first time using OH Planar Laser-Induced Fluorescence (OH-PLIF) and Mie scattering simultaneous measurements. The two-phase measurement of LNH₃ flames features a unique single flame structure with limited droplet–flame interaction. Three types of droplet–flame interactions are identified, and the influence of the Reynolds number on flame structure is discussed. Temperature measurements indicate both moderate evaporation and flash boiling were found during the combustion. These findings provide valuable insights into LNH₃ flame structure and offer validation data for the development of numerical models. Novelty and Significance Statement This study presents the first revelation of the LNH₃ jet spray flame structure in a hot and low-oxygen environment. Unlike hydrocarbon fuels with a “double flame” structure, the LNH₃ jet flame displays a “single flame” structure due to rapid droplet evaporation. Three types of droplet–flame interactions were identified. 97.46% of droplets show no significant interaction with flame in a typical condition. It is also confirmed that the co-existence of moderate evaporation and fast flash boiling of LNH₃ during combustion. The Re number of carrier air significantly affects droplet distribution and evaporation, influencing spray structure and flame characteristics. This study provided valuable insights into the two-phase characteristics of LNH₃ spray jet flame and validation data for numerical simulations.