Understanding the thermoacoustic response of swirling spray flames fed with a surrogate of sustainable aviation fuel

Due to their multicomponent composition, fuels are challenging in thermoacoustic instability analysis, particularly sustainable aviation fuels (SAFs) sought as drop-in fuels. Understanding their dynamics is essential to prevent undesirable consequences in aircraft engines. This requires full comprehension of how each constituent of the liquid fuel affects combustion dynamics through atomization, evaporation, mixing with air, and ignition. This paper investigates a two-component SAF surrogate, composed of dodecane and isooctane, supplying three swirling spray flames subjected to a standing transverse acoustic mode. Results are compared with those of the pure constituents and n-heptane, used as a reference fuel. Using the downstream pressure-based flame describing function, the dynamical responses of isooctane and dodecane are found to be less efficient than n-heptane, and the SAF surrogate’s response is weaker than its pure constituents. Phase Doppler Anemometry measurements highlighted dodecane’s low evaporation rate and showed that the behaviors of isooctane and SAF surrogate cannot be explained solely by evaporation. High-speed OH* imaging showed longer flames for isooctane than for dodecane and n-heptane, while the SAF surrogate produced the longest. Compared to n-heptane, the region of maximum flame intensity oscillations ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mi>R</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> ) is weaker and shifted downstream for dodecane and isooctane, promoting more localized flame spreading outside the Rayleigh instability band. This attenuation effect is even more pronounced for the SAF surrogate. The different flame structures and responses arise from evaporation delay in dodecane, ignition delay in isooctane, and a combined effect of both in the SAF surrogate.