Spray and combustion characteristics of Diesel/Polyoxymethylene dimethyl ethers (PODE_n) Mixtures: Role of CH₂O chain length in PODE_n

Polyoxymethylene dimethyl ethers (PODE_n) are promising synthetic fuels (e-fuels) with the potential to decarbonize the heavy-duty and marine sectors. However, it is unclear how blending monomolecular PODE_n with different CH₂O chain lengths affects the diesel spray. This study therefore compares the spray and combustion characteristics of neat diesel and diesel/PODE_n blends (blending with three monomolecular PODE_n for n = 2, 3, 4 at a constant percentage of 20 % by volume) under non-evaporating, evaporating, and burning conditions. The finding suggests that diesel/PODE_n blends are more advantageous to spray quality than diesel fuel under the non-evaporating condition because they demonstrate an increasing trend in spray tip penetration, cone angle, and area. Blends with longer CH₂O chain lengths in PODE_n present a longer spray tip penetration but a smaller spray cone angle and spray area. Under the evaporating condition, substituting diesel with PODE_n containing a longer CH₂O chain length generally increases the maximum liquid-phase penetration length of blended fuels, together with a slightly accelerated spray cone angle and spray area, indicating a lower evaporation rate. Shorter ignition delay and flame lift-off length while increased flame area are observed with the increasing CH₂O chain length in PODE_n. A trade-off relationship occurs between the influences of the CH₂O chain lengths in PODE_n on soot generation of diesel/PODE_n blends, which leads to slight discrepancies in soot concentration (KL factor).