Spray and flame characteristics of diesel/n-butyl ether blend fuels through optical measurement

Diesel combustion produces multiple pollutants. Di-n-butyl ether (DBE), a biomass-derived clean fuel, can be used directly in diesel engines. This study uses a constant-volume combustion chamber (CVCC) to investigate the spray and combustion characteristics of diesel/DBE blended fuels (D90DBE10, D80DBE20, D70DBE30, D60DBE40) and compares them with pure diesel (D100). This study focuses on the effects of injection pressure (100–140 MPa), ambient temperature (300–700 K), and DBE blending ratio. Results indicate that DBE addition significantly improves fuel atomization. The spray cone angle (SCA) and spray projected area (SPA) of blended fuels exceed those of D100, while the spray tip penetration (STP) is shorter. When the injection pressure is increased from 100 to 140 MPa, the liquid phase spray projected area (L-SPA) and gas–liquid phase spray projected area (GL-SPA) of D100 expand by 17.31% and 9.32%, respectively, while those of D60DBE40 increase by 27.84% and 8.65%, respectively. The blended fuels exhibit faster flame development and lower soot formation, with D60DBE40 demonstrating the fastest flame propagation and lowest soot radiation. At 140 MPa injection pressure, the KL factor for all blended fuels decreases by 12.62%–16.87% compared to D100. The study indicates that DBE promotes cleaner and more efficient combustion processes, offering a viable fuel optimization pathway for reducing diesel engine soot emissions.