Sustainable aviation fuels (SAFs) derived from renewable sources are promising
solutions for achieving carbon neutrality and further controlling aircraft
engine emissions, operating costs, and energy security. These SAFs, primarily
consist of branched and normal paraffins and exhibit significantly reduced
sooting tendencies compared to conventional petroleum-based jet fuels, due to
their lack of aromatics content. Our previous study investigated soot formation
in non-premixed combustion for three ASTM-approved alternative jet fuels, namely
Fischer–Tropsch synthetic paraffinic kerosene (FT-SPK), hydroprocessed esters
and fatty acids from camelina (HEFA-Camelina), and alcohol-to-jet (ATJ), and
demonstrated that the varying paraffinic composition within SAFs results in
diverse sooting propensities, in the order of ATJ > FT-SPK >
HEFA-Camelina. To evaluate the impact of iso-paraffins on sooting tendency and
validate the suitability of utilizing binary blends of iso-dodecane (iC12) and
normal dodecane (nC12) as surrogates for emulating sooting characteristics of
SAFs, an experimental study was conducted to measure the soot volume fraction
profiles of iC12/nC12 blends with varying blending ratios in the counterflow
non-premixed flame configuration using laser-induced incandescence technique. It
is shown that ATJ and HEFA-Camelina can be well-represented by pure iC12 and the
blend of 25% iC12 and 75% nC12 (in liquid volume), respectively. At high (low)
reactant concentrations, the blend of 75% iC12/25% nC12 (90% iC12/10% nC12)
exhibits similar sooting characteristics of FT-SPK. The present experimental
results indicate that binary blends of iC12 and nC12 have the potential to serve
as effective surrogates for SAFs, as they are predominantly composed of these
two types of paraffinic components. Furthermore, it is found that when the iC12
blending ratio exceeds 90%, the maximum soot volume fraction exhibits a stronger
nonlinear increase. This experimentally observed nonlinearity in maximum soot
volume fraction with increasing alkane branching in the binary fuel blend
signifies the importance of fuel molecular structure effects on soot formation
pathways in counterflow non-premixed flames.
