“…Premixed and non-premixed regions in swirl spray flames were analyzed with the flame index concept (Eckel et al 2019;Paulhiac et al 2020) and the influence of swirl number on the combustion regime (Fredrich et al 2019) was evaluated. It was used to study different coal flames (Tufano et al 2018;Wan et al 2019;Rieth et al 2019;, assess the stabilization mechanism of supersonic lifted flames (Bouheraoua et al 2017) and lifted hydrogen flames (Benim et al 2019), classify regions of industrial burners by the combustion regime , study auto-ignition of supercritical hydrothermal flames (Song et al 2019), analyze extinction and re-ignition events (Sripakagorn et al 2004) and gain insight into partially premixed DME flames . It was further applied to scram jets (Shen et al 2020;, Moderate or Intense Low oxygen Dilution (MILD) combustion (Amaduzzi et al 2020), compression ignition engines (An et al 2018), double-cone burners , coaxial diffusion flames , edge flames (Duboc et al 2019) and jet-in-hot-coflow flames in conjunction with tangential stretching rate analysis (Li et al 2019).…”