The objective of this work was to investigate the effect of fuel properties on atomization and spray structure of a diesel engine fuel injector, based on PDA (Phase Doppler Anemometry) measurements. Few studies have addressed the question of how fuels affect droplet size and spray structure. Thus three diesel fuels were selected: two which broadly represent the range of base fuel properties seen in current European fuels and a third which contained a high treat rate of a detergent-type additive, which, being polar, may have some surface effects which could impact spray formation.
This range of diesel fuels was injected into a high pressure and temperature wind tunnel, using a single hole Bosch injector. Phase Doppler Anemometry (PDA) was used to measure the diameter, velocity and arrival time of spray droplets passing through numerous radial and longitudinal positions in the spray. Most data were collected under quiescent conditions, but an additional number of measurements were made on fuel injected into the tunnel with a gas cross-wind. Not only is this cross-flow representative of many engines, but it enables separation of the droplet sizes based on mass and cross-section, winnowing smaller droplets from the denser core. Careful attention was given to data validation and the incorporation of repeat tests over a long time period, to ensure the data were reliable and could be evaluated statistically.
No difference in droplet diameter larger than the repeatability of 3μm could be detected either for fuels varying in density, volatility and viscosity, or additised with a high treat rate of a detergent-type additive. However, there were small differences between these fuels which could be detected: there was evidence that the fuel treated with detergent additive produced a narrower more penetrating spray. While these effects are not currently understood, it is possible that the detergent may influence the flow inside the nozzle.