A spray from a GDI multi-hole injector operated in ambient air at known fixed conditions, is studied with different experimental techniques to better understand the spray behaviours. The analysis is focussed on the effect of the fuel temperatures on five different tested fuels: three pure fluids, namely pentane, hexane and N-heptane, and two gasolines with known distillation curves. Results on the whole spray from photographic imaging, and on droplet velocity and sizing on a single plume by Phase Doppler Anemometry are presented and compared. With the pure components, the images show that the temperature increase gives a negligible effects up to the boiling point of the specific tested fuel at the ambient air pressure; slightly above that temperature the typical step change caused by flash boiling is observed in the spray structure, with the collapse of the different plumes in a unique spray. The gasolines show this behaviour at a temperature that is much closer to that of the hexane. The spray droplet are measured at 45mm of axial distance from the injector tip in 13 different radial positions; after data post-processing the average velocity and diameters results are plotted, both as time evolution in a fixed position, and as radial profiles during the quasi-steady injection period. The structure change with the increasing temperature is more evident and easy to quantify: the velocity profile clearly shifts towards the centre of the collapsing spray, while the droplet velocity and size decreases.
PDA measurement in a GDI spray: effect of the temperature on different fuels
2017
Abstract
A spray from a GDI multi-hole injector operated in ambient air at known fixed conditions, is studied with different experimental techniques to better understand the spray behaviours. The analysis is focussed on the effect of the fuel temperatures on five different tested fuels: three pure fluids, namely pentane, hexane and N-heptane, and two gasolines with known distillation curves. Results on the whole spray from photographic imaging, and on droplet velocity and sizing on a single plume by Phase Doppler Anemometry are presented and compared. With the pure components, the images show that the temperature increase gives a negligible effects up to the boiling point of the specific tested fuel at the ambient air pressure; slightly above that temperature the typical step change caused by flash boiling is observed in the spray structure, with the collapse of the different plumes in a unique spray. The gasolines show this behaviour at a temperature that is much closer to that of the hexane. The spray droplet are measured at 45mm of axial distance from the injector tip in 13 different radial positions; after data post-processing the average velocity and diameters results are plotted, both as time evolution in a fixed position, and as radial profiles during the quasi-steady injection period. The structure change with the increasing temperature is more evident and easy to quantify: the velocity profile clearly shifts towards the centre of the collapsing spray, while the droplet velocity and size decreases.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
