Abstract: Abstract: In order to improve the atomization quality of biodiesel and diesel-biodiesel blends containing dissolved gas, the Phase doppler particle analyzer(PDPA, a device that can accurately measures the diameter and velocity of droplets in a spray field)was used to analyse the atomization quality of diesel-biodiesel with and without dissolved gas in this paper. The PDPA measurement system was used to test mixed fuel with different volume ratios(B0、B30、B50、B70、B100) at nozzle diameters of 0.24 and 0.30 mm. The axial velocity and particle size distribution were measured and analyzed. Further, based on the mixed fuel, different volumes of CO2 were dissolved therein, and the percentage of dissolved gas in volume was 5.74%, 12.73% and 26.42%, respectively, and the atomization quality of the fuel containing CO2 was measured at nozzle diameters of 0.24 and 0.30 mm. The results showed that at a nozzle diameter of 0.24 mm and 0.30 mm, the sauter mean diameter(SMD) of the biodiesel was greater than that of diesel, the average diameter of diesel fuel was 25 μm lower than that of biodiesel at the axial length of 70 mm, the atomization quality of the mixed fuel was obviously improved compared with that of biodiesel, with the decrease of nozzle diameter , the atomization quality was greatly improved. When the volume content of CO2 was 26.42%(C26.42), the droplet size at the axial length of 70 mm was 13.1 μm smaller than that of B50. The droplet size of the B50 with dissolved gas volume ratio of 5.74%(C5.74) and 12.73%(C12.73) was 5.3 and 12.2 μm higher than that of B50 at the axial length of 70 mm, respectively. When the nozzle diameter was reduced from 0.30 mm to 0.26 mm, C5.74 and C12.73 had a greater inhibitory effect on atomization and the SMD increased by 8.43% and 6.82%, respectively. The atomization quality of C26.42 was enhanced as the nozzle diameter reduced and the SMD was decreased by 26.5%. The fuel that contains a small amount of CO2 had a larger SMD than that of the fuel without dissolved gas, and the inhibition effect on atomization was more obvious with the decrease of nozzle diameter. When the amount of dissolved gas was high, the atomization quality was promoted, and with the decrease of nozzle diameter, the promotion effect was enhanced. This study showed that dissolved gas can improve the atomization quality of biodiesel under certain conditions, dissolved gas in mixed fuel can overcome the disadvantages of high viscosity and density of biodiesel, improve the atomization quality of biodiesel and improve its combustion effect, biodiesel can be better used in internal combustion engines.