Insight into the macroscopic and microscopic characteristics of high-pressure polyoxymethylene dimethyl ethers (PODEn) spray in hydrogen-doped environments

Hydrogen (H2)/polyoxymethylene dimethyl ethers (PODEn) dual-fuel engines provide a promising scenario to realize near-zero carbon emissions in the transportation sector over the world. Compared with conventional fuels, the unique thermophysical properties of H2 as a premixed fuel can significantly influence the spray development process of PODEn in engines. This study comprehensively investigates the macroscopic and microscopic characteristics of high-pressure PODEn spray under various H2-doping conditions with high-speed imaging and phase Doppler particle analyzer techniques in a constant volume bomb. The experimental results from the high-speed image indicated that with the increase in H2-doping fraction, the vortex zone on both sides of the spray head becomes weaker, and a distinct zone with dilute droplets is observed in the vicinity of the spray/gas interface. At the spray axial position of 40 mm under the non-H2 doping situation, the number of relatively larger droplets with the diameter over 60 μm gradually reduces with the increase in the radial distance from the spray axis, since the increased shear force on the fuel jet near the spray interface, facilitating the droplet breakup. With the radial distance further increased to 4 mm, some larger droplets with the diameter exceeding 80 μm appear, since the relatively stronger vortex motion near the spray tip promotes the droplet coalescence. With the increase in H2-doping percentage, the arithmetic mean diameter and Sauter mean diameter of droplets are significantly reduced attributed to the enhanced Rayleigh–Taylor instability relevant to the lower density of ambient gas promoting the droplet breakup.