Fast video photography and image analysis were used to compare the effect of fuel and mixture preparation variables on the relative quantities of liquid droplets present in the combustion chamber of a port fuel-injected engine. The injection timing and swirl conditions were varied and a fluorinated surfactant was also added to a standard gasoline. Swirl enhanced evaporation. The surfactant decreased the light scattering. There is some indication that swirl and additive together are mutually antagonistic and work against their individual beneficial effects on mixture preparation.