Spray-tip droplet SMDs of intermittent high-pressure sprays of diesel fuel compared with coal-water slurry sprays

摘要

An experimental study investigated droplet-size characteristics near the spray tip of intermittent sprays of diesel fuel from an electronically controlled accumulator injection system. A modified laser-diffraction particle-analysing technique (Malvern 2600C system) optically synchronised the data taken with the spray penetration, so that the Sauter Mean Diameter (SMD) could be measured at low obscurations without multi-scattering bias. Measurements were made at axial locations 60, 80,100 and 120 mm downstream of the injector orifice with 0.2 and 0.4 mm diameter orifices. Injection pressures studied were 28, 56, and 83 MPa g, and measurements took place in both pressurised (2.07 MPa g) and unpressurised chamber conditions. The spray-tip SMD increased with ambient gas density and axial measurement location, and fell inversely with injection pressure. Dependence of SMD on nozzle orifice diameter was negligible for fully developed sprays. A regression equation for the SMD (μm) was found as SMD = 1.402ΔP~(-0.451)ρ_a~(0.1588)x~(0.8977) where ΔP is in MPa gauge, ρ_a is the ambient gas density in kg m~(-3), and x is the axial measurement location in mm. These results show characteristics consistent with previous studies where coal-water slurry was the atomised liquid. Quantitatively, under identical injection conditions the droplet SMDs of diesel sprays were always smaller than those of coal-water slurry. Parametric comparisons for the two types of injected fuels are presented.