The influence of fluid properties on near nozzle sprays in clean and fouled GDI injectors

Physical fluid properties and GDI injector deposits are known to impact the internal nozzle flow and external spray morphology. Furthermore, deposits can affect injector calibration and damage the delicate mixing and combustion processes. Despite this, there is a lack of experimental data demonstrating the discrete influence of fluid properties and how this influence evolves with the formation of injector deposits. This article aims to further the existing knowledge on the effect of fluid properties such as density, kinematic viscosity and surface tension, along with distillation on fuel spray characteristics and provide insight into how sprays change over the lifetime of GDI injectors due to fouling. In this investigation, four gasoline fuels with varying concentrations of ethanol and typical GDI additive, including one being representative of a renewable gasoline formulation, were used with clean and fouled multi-hole GDI fuel injectors. A low-pressure constant-volume chamber was used to produce a controlled inert atmosphere at various ambient and injection conditions. Shadowgraph images were recorded using two high- speed cameras at the micro and macro scales to simultaneously visualise the fluid dynamic processes in the near nozzle and downstream regions. Image analysis demonstrated that fouling had a significant impact on the spray angle. Standard error of the mean was used to determine the repeatability of the measurements taken, and it was found that the spray width at the nozzle tip had a very low standard error. In contrast, a comparatively high standard error was calculated for spray dispersion angle exhibited for the fouled and clean injectors. Due to high repeatability on spray width measurements, positive correlations were found between the spray width at the nozzle tip and initial boiling point, surface tension and kinematic viscosity, and negative correlations with density and final boiling point.