The initial mechanism of cellular instabilities on the flame surface was investigated experimentally. Firstly, mono-dispersed ethanol droplets were created via the Wilson cloud principle in a spherical combustion chamber, and aerosol ethanol/air flame propagation was tracked under microgravity conditions. Schlieren images revealed that at the beginning of the cellular structure formation, dark spots formed linking to the signal loss in a density gradient. This phenomenon is assumed to be local extinction and quenching on the flame front due to either liquid droplets' presence or evaporation. To further investigate the observed phenomenon, stagnation flame experiments were performed for rich propane/air gaseous flames with isolated ethanol droplet injection. The evidence for the local extinction on the flame surface due to droplet passage was found via the Chemiluminescence method. The intrinsic instabilities were found to be triggered by the droplets in cases where the flame cannot recover its initial state.

The aim of this study is to investigate single ethanol droplet evaporation characteristics under premixed CH4/air flame conditions via experimental and numerical approaches. In the experimental part of the study, ethanol droplet with an initial diameter between 20 and 70 ~m was injected through a flat laminar stagnant flame. Visualization of the flame front and temporal monitoring of the droplet evaporation at high temperatures up to 2200 K were performed using planar laser tomography. Droplet motion and its diameter change are captured simultaneously via PIV /pTV and IUDS diagnostics, respectively. Velocity measurements indicated that the droplets are small enough to be carried by surrounding gas with a very small slip velocity. Variation in droplet diameter is successfully tracked through the flame via IUDS and it is found to be more drastic in burnt gases. Hence, vaporization rates are reported at burnt gas temperature which is affected by the heat losses from flame to the stagnation plate due to the change in the temperature profile. In the numerical part of the study, single droplet evaporation under constant temperature and stagnant environment was studied with Spalding model using YALES2 solver. The variations of the droplet properties were computed under N2 atmosphere and under flame conditions. At elevated conditions, flame temperature is found to have a more dominant effect on the evaporation rate rather than the burnt gas composition.