Abstract: The spray and combustion characteristics of the fuel affects the fuel/air mixture formation process, which subsequently influences the in-cylinder combustion process and pollutant generation. Polyoxymethylene dimethyl ethers (PODE_n) have emerged as promising alternative fuels for diesel engines, offering potential for decarbonizing agricultural applications. However, the impact of blending PODE_n with various CH₂O chain lengths on diesel spray characteristics remains unclear. Therefore, this paper investigates the effects of PODE with different CH₂O chain lengths on the spray combustion characteristics of diesel fuel. The spray combustion characteristics of three fuel blends, diesel/PODE₂, diesel/PODE₃ and diesel/PODE₄ were compared under various ambient conditions and different injection pressures. The experiments were conducted in a visualized constant volume combustion chamber, capturing spray development images via the schlieren method and combustion images through direct photography. Homemade software was utilized to extract spray parameters such as spray tip penetration, spray cone angle, and spray area from the schlieren images, while spray combustion parameters, including ignition delay times, flame lift-off length, and integrated natural flame luminosity, were derived from the combustion images. The results revealed that the addition of PODEn increased spray tip penetration but decreased both the spray cone angle and spray area. As the CH₂O chain length in PODE_n increased, the spray tip penetration of the diesel/PODE_n blends further increased. It is attributed to the higher density of the fuels, which plays a more significant role than kinematic viscosity in the fuel atomization process. Meanwhile, the spray cone angle decreased with increasing CH₂O chain length, suggesting that kinematic viscosity might dominate this parameter. The spray area exhibited an increasing trend with longer CH₂O chain lengths, resulting from the combined effects of spray tip penetration and spray cone angle. Additionally, an increase in injection pressure led to a rising trend in spray tip penetration, spray cone angle, and spray area for the blended fuels. At an ambient temperature of 823 K and the air atmosphere, the integrated natural flame luminosity decreased as the CH₂O chain length in PODE_n increased from 2 to 4. It is attributed to the enhanced oxidation of free radicals due to the increased oxygen content in the blended fuel, reducing soot generation. Furthermore, both ignition delay times and flame lift-off length were significantly shortened. With higher injection pressures, the integrated natural flame luminosity and ignition delay decreased significantly for the tested fuels. Notably, the integrated natural flame luminosity, ignition delay, and flame lift-off length all decreased significantly with increasing CH₂O chain length. In conclusion, the incorporation of PODE_n enhances diesel fuel atomization, improves ignition characteristics of diesel fuel sprays, and reduces soot emissions. Moreover, longer CH₂O chain lengths in PODE_n are conducive to further reducing soot emissions. This study provides valuable insights for the application of PODE_n as a suitable and promising alternative fuel in high-pressure common rail agricultural diesel engines.