Experimental investigation into the spray interaction and combustion characteristics of biodiesel/methanol dual-fuel sprays

This study presents the first systematic optical investigation of spray interaction and combustion characteristics in biodiesel/methanol dual-fuel direct injection system, conducted in a constant‐volume combustion chamber using Schlieren imaging. Individual biodiesel and methanol spray behaviors were first compared under non‐reactive conditions at injection pressures of 60, 80, and 100 MPa, revealing that biodiesel sprays exhibit longer penetration and narrower cone angles, whereas methanol sprays show finer atomization and wider dispersion. Dual‐spray collision and combustion characteristics were then analyzed by varying injection intervals (Δt) and sequencing. Results indicate that increasing Δt reduces spray penetration at 60 MPa while enhancing it at 100 MPa. Maximum spray area and lateral dispersion occurs at Δt = 1.0 ms; beyond this, spatial decoupling limits atomization efficiency. The collision length decreases with increasing Δt, while collision width peaks at Δt = 1.0 ms. Methanol-first injection induced localized cooling due to its high latent heat, delaying biodiesel evaporation. In contrast, biodiesel-first injection produced a more cohesive initial spray, followed by rapid methanol dispersion, enhancing overall mixing and spray area. At 100 MPa, longer Δt reduces spray overlap and interaction, while shorter intervals facilitate greater jet convergence and larger spray areas. Ignition consistently initiates at the spray interaction region, with flame morphology and luminosity strongly influenced by injection strategies. Methanol‐first strategies facilitates early ignition but suppresses subsequent biodiesel ignition due to the evaporative cooling, whereas biodiesel‐first strategies yield higher overall flame luminosity due to soot formation. This work provides new quantitative insights into how injection parameters affects dual-spray collision and combustion performance, offering practical guidance for optimizing injection strategies in renewable dual-fuel engines.