Topology transition of the multiphase reacting flow in a Lean Azimuthal Flame (LEAF) combustor*

The pressing need to reduce the aviation carbon footprint has propelled several research endeavors to develop new combustor concepts aiming at clean combustion of sustainable aviation fuels (SAF). The current work presents the flame characteristics in a Lean Azimuthal Flame (LEAF) combustor, which has shown ultra-low NOx and soot-free liquid fuel combustion. In the presented work, three Jet-A1 sprays are injected axially into a whirling main airflow, where the interaction between them leads to a spray in a vitiated crossflow configuration. The continuous entrainment and mixing of hot products result in the sequential combustion of the sprays by each other. The combustor is investigated for the Jet-A1 thermal power range from 15 kW to 25 kW, with varying atomization-air to liquid mass flow ratio (ALR) using OH-chemiluminescence, Mie scattering, and OH-PLIF. The flame shows the LEAF configuration at high ALRs, whereas, at low ALR, the flame exhibits a tubular topology. It is shown that the convective and spray evaporation timescales are the two prominent parameters that govern the observed flame behavior. A simple model based on empirical correlation is derived, allowing us to predict the change of flame topology associated with the ALR variation in this complex LEAF configuration.