The research on the effect of different alternative fuels on the injection characteristics of a double-layer eight-hole injector with needle eccentricity

Abstract

Accurate prediction of in-nozzle flow with alternative fuels is essential to improving spray atomization, combustion efficiency and emission control in modern diesel engines. Three-dimensional computational-fluid-dynamics simulations, based on a validated two-fluid cavitation model, were performed for a double-layer eight-hole injector supplied with six fuels—petroleum diesel (B0), Polyoxymethylene dimethyl ether (PODE), Biodiesel, n-Butanol, Butyl formate and n-Octanol—under both concentric and eccentrically guided needle motions. Findings reveal that fuel density governed the mass-flow rate in the concentric case: the densest fuel, PODE (1053 kg m⁻³), delivered a 14 % higher mass-flow rate than the least-dense n-Butanol (813 kg m⁻³), whereas the ordering of volumetric flow rates was reversed. With a 0.06 mm needle offset, viscosity influenced the cavitation development: cavitation onset for the most viscous n-Octanol (5.65 mm² s⁻¹) lagged that of the least-viscous Butyl formate (0.61 mm² s⁻¹) by 0.15–0.20 ms. Outlet Reynolds numbers spanned 9.8 × 10³ to 9.1 × 10⁴ across fuels, underscoring the strong influence of thermophysical properties. Needle eccentricity emerged as the dominant source of flow non-uniformity, producing up to a 12 % disparity in cycle fuel injection quantity between upper- and lower-layered orifices and as much as a 6 % disparity among holes within a layer, independent of fuel type; the upper-layered hole consistently exhibited a 4–7.5 % lower liquid-phase fraction than the lower-layered hole. These results provide the first quantitative picture of the coupled effects of needle eccentricity and diverse fuel properties on multi-layer injector performance, identifying eccentricity—not fuel formulation—as the principal driver of injection non-uniformity.