This work aims to compare the droplet size distribution features of DME/diesel blended fuels and conventional diesel oil by using a high-resolution digital camera in combination with image processing techniques. Based on the acquired size distribution data, microscopic spray characteristics including the mean diameter, the characteristic diameter, and the relative span factor can be thereby calculated to evaluate the spray quality of the test fuels. According to the experimental results, finer spray droplets can be observed for blended fuels compared with diesel spray, which probably owes to the flash boiling effect of DME in diesel when injected out of the nozzle exit. In addition, when the mass fraction of DME increases from 10% to 20%, the corresponding droplet size distribution curve moves toward smaller diameters and the number of large droplets reduces simultaneously, indicating that the spray quality can be improved by DME addition. As for microscopic spray characteristics, it is found that blending DME in diesel causes considerable reduction in the mean diameter and the characteristic diameter. Meanwhile, the result shows an increased relative span factor as the mass fraction of DME increases, which is mainly because large droplets still exist for blended fuel cases, although the absolute number is reduced by DME addition.
