Large Eddy Simulation of Thermo-Acoustic Instabilities of Bluff-Body Stabilized Flames; A Comparison Between Jet-A and C1

Due to the threat climate change poses, the aviation industry needs to adapt. In the process to convert the aviation fleet into a more environmentally friendly fleet, using biofuels such as Sustainable Aviation Fuels as a drop-in fuel remains a promising option. To include biofuels, safety aspects need to be investigated, where combustion instabilities are important. Thermo- acoustic instabilities are widely regarded as one of the most important combustion instabilities in combustors. Here, Jet-A and C1 are numerically compared using Large Eddy Simulations with Finite-Rate Chemistry and pathway-centric skeletal reaction mechanisms Z79 and Z153. The simulations capture the thermo-acoustic instability well with good agreement with exper- imental results. Z153 provides a better limit-cycle behavior for C1, whilst Z79 provides an accurate transition point for thermo-acoustics. Z153 might yet accurately capture the transi- tion point, however, the simulations required to validate this is left for future work. Gas dila- tation images provide information regarding its proximity to the recirculation zone. Once thermo-acoustic instabilities are present, the gas dilatation is present in the recirculation zone. To obtain thermo-acoustics, the f_1L needs to couple with f_HD, which occurs either when the frequency detuning is small, or if the amplitude of the acoustics is large enough. Z153 provided a better propagation speed of the flame such that the detuning decreased through an increased effective speed of sound, and therefore the coupling strengthened resulting in a larger ampli- tude, as seen in the experiments.