The morphology on the large amplitude oscillatory shear rheological behaviors of hydrocarbon-based gel fuels: A case of study for spherical and flake aluminum particles

Aluminum (Al) particles have been extensively filled into conventional liquid and solid fuels to improve energy density. However, introducing these particles will modify the rheological properties of hydrocarbon-based gel fuels (GFs). A comprehensive understanding the nonlinear rheological behaviors of GFs is essential, because the utilization of GFs often involves large deformation. In this study, the effects of flake and spherical aluminum (FAl and SAl) particles on the nonlinear responses of hydrocarbon-based GFs were investigated by large amplitude oscillatory shear (LAOS) at different frequencies. The solid-liquid transition behavior was characterized by Lissajous-Bowditch (L-B) curves and Fourier Transform-rheology. Stress sweep results revealed that GFs containing FAl particles exhibited significant viscoelastic characteristics than GFs containing SAl particles. The L-B curves demonstrsted that increasing the SAl particles content slowed transition from linear to nonlinear response, whereas higher FAl particles concentration accelerated this transition. Based on the stress softening ratio (R) and shear thinning ratio (Q), GFs containing FAl particles showed more significant stress stiffening and shear thickening than GFs with SAl particles as aluminum particles content increased. The higher harmonics ratio indicated that nonlinear responses were intensified with increasing FAl particles concentration. while this trend was reversed in GFs containing SAl particles.