Experimental investigation on spray and combustion characteristics of dual-fuel collision of biodiesel and n-butanol

Abstract

The sprays collision phenomena exist in many diesel engines with two or more injectors. In the dual direct injection strategy, the dual-fuel collision can realize different concentrations and reactivity stratification, which is beneficial to control the ignition and combustion processes. The investigation aims to explore the spray and combustion characteristics of collision biodiesel and butanol at different collision angles (90°, 120° and 150°), injection pressures, and ambient conditions. The experiments are conducted in a constant-volume combustion chamber with two independent injection systems. The collision spray and combustion images are captured by optical diagnosis techniques. Several macroscopic parameters are obtained, including collision length, collision width, spray area, gray value level, ignition delay, ignition location, flame lift-off length, flame area, and natural luminosity intensity. Results show that after the collision, the spray in the horizontal direction has faster evaporation and diffusion rates compared with the spray in the vertical direction. The horizontal diffusion rate of vapor-phase spray is about 1.2 times the vertical diffusion rate. Meanwhile, increasing the ambient temperature has a more positive impact on promoting the horizontal diffusion of vapor-phase spray, and the horizontal diffusion is less hindered by the ambient gas resistance and increased collision angle. At larger collision angles, higher relative velocity leads to intenser collision process and smaller diffusion rate after the collision owing to larger collision loss and smaller vertical velocity component. A smaller equivalence ratio after the collision leads to longer ignition delay and shorter flame lift-off length, which contributes to intenser combustion process and higher soot emissions. Meanwhile, increasing the injection pressure can improve the ignition and combustion characteristics, but the improvement in reducing the soot emission is suppressed at larger collision angles.