Abstract: Biodiesel is commonly used in diesel engines for soot reduction due to the intramolecular oxygen. However, its higher viscosity and surface tension negatively affect the droplet fragmentation and further worsen the atomization quality and spray performance. In this study, acetone-butanol-ethanol (ABE) was blended with biodiesel to decrease its viscosity and surface tension and improve its volatility. A constant volume combustion chamber was adopted to explore the effects of different ABE blending ratios, ambient temperatures and ambient pressures on the macroscopic spray characteristics of ABE/biodiesel blended fuels. Furthermore, proper orthogonal decomposition (POD) was employed to quantitatively characterize the structural instability. The experimental results indicate that the addition of ABE can effectively optimize the spray atomization and evaporation performance. With the increase of ABE blending ratio, the viscosity and surface tension of blended fuels decrease significantly. Correspondingly, the spray tip penetration decreases, while the spray cone angle and spray projected area increase obviously. At the ambient temperature of 500 K, the peak spray cone angle of 30% ABE blended fuel is (22.3 degrees) 5.1% higher than that of pure biodiesel (21.2 degrees). Ambient temperature and ambient pressure exert significant regulatory effects on the spray characteristics of ABE/biodiesel blended fuels, and exhibit favorable synergistic effects with ABE blending modification. Specifically, at 800 K, the 30% ABE blended fuel achieves a 15.6% higher spray cone angle and a 19.5% larger peak spray projected area compared with pure biodiesel. Elevated ambient pressure increases ambient gas resistance, inhibits axial spray penetration, and promotes radial diffusion and secondary droplet breakup, further improving the atomization quality of blended fuels.As the ABE blending ratio increases, the Reynolds (Re) and Weber (We) numbers rise while the Ohnesorge (Oh) number decreases, indicating intensified jet turbulence, which makes primary and inertial-capillary breakup more likely and facilitates the generation of fine droplets. POD analysis reveals that the distribution of coherent structure motion directions in the spray field becomes more random and complex with the addition of ABE. As ABE blending ratio rises, the energy proportions of the first-order mode decline, while those of higher-order modes increase. At 800 K, the first-order mode energy proportion of pure biodiesel is 45.91%, while that of 30% ABE blended fuel is only 36.30%. This shows that increasing the ABE proportion enhances the interface fluctuation and the complexity of the spray structure. These findings show that the addition of ABE improves the spray characteristics compared with pure biodiesel, and provides a method for thoroughly substituting diesel with biomass fuels. By combining the benefits of ABE and biodiesel, the blended fuels offer a promising solution for promoting sustainable energy use in the transportation sector. These findings demonstrate that ABE addition can effectively improve the spray characteristics of biodiesel, providing a feasible technical route for the application of biomass-based fuels in diesel engines, especially for clean-energy upgrade of agricultural equipment and transportation.