Experimental Evaluation of Binary Iso-Dodecane/n-Dodecane Blends for Emulating Sooting Characteristics of Sustainable Aviation Fuels

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.