Flash-boiling sprays in gasoline direct injection (GDI) engines play a pivotal role in achieving efficient fuel-air mixing, yet their dynamics under superheated conditions remain poorly understood, particularly for multi-component fuels. This study bridges this gap by employing advanced X-ray phase-contrast imaging (XPCI) and schlieren techniques to investigate ethanol and gasoline sprays, offering unprecedented insights into near-nozzle and downstream behaviors. The work reveals that ethanol’s distinct single-component properties trigger unambiguous flash-boiling phenomena (e.g., plume merging, upward curling), while gasoline’s complex composition suppresses homogeneous phase change, challenging conventional flash-boiling frameworks. XPCI captures persistent liquid cores near the nozzle exit under superheating—a critical yet overlooked feature—highlighting the interplay between inertial forces and vaporization kinetics. The study further demonstrates how flash boiling redistributes spray momentum, enhancing radial dispersion while reducing axial penetration, with implications for mitigating tip wetting and wall impingement. By correlating droplet size, velocity profiles, and phase-change dynamics, this research not only advances and refines the fundamental understanding of flash-boiling atomization but also provides actionable insights for optimizing combustion efficiency and reducing emissions in next-generation GDI engines.