The influence of superheated injection on liquid and gaseous flow field of an experimental single-hole gasoline direct injection injector

Abstract

In modern gasoline direct injection engines, the fuel is (partially) superheated for a significant proportion of the time during operation. This means that the vapour pressure of the fuel, or at least of many of its components, is higher than the ambient pressure inside the engine during injection. If the excess fuel enthalpy cannot be removed by evaporation at the free surface of the spray, the liquid phase boiling creates new surfaces. This phenomenon is known as flash boiling. Flash-boiling atomization produces smaller droplets and can therefore be beneficial as an additional atomization mechanism. Furthermore, it can reduce the penetration depth of a spray, although it also decreases the stability of fuel sprays. This is manifested in undesired targeting changes, that is, spray contraction due to jet-to-jet interaction. In extreme cases, a complete spray collapse can occur, where a multi-hole or hollow-cone spray contracts towards the spray axis and forms a jet-like structure that increases penetration depth. To understand the relationship between flash-boiling atomization and targeting changes, flash boiling was investigated with a single-hole generic injector without jet-to-jet interaction. In addition to macroscopic spray parameters, this study also focused on the flow field of the spray itself measured using laser Doppler anemometry, as well as the spray-induced flow field of the surrounding gas phase measured using fluorescent particle image velocimetry. The results show a strong radial expansion of the jet directly after nozzle exit, caused by internal flash boiling. It is shown that this expansion is caused by a zone of expanding fuel vapour in the centre of the spray. As a result, the displacement of air after injector opening as well as at the front of the spray is significantly increased, causing a decrease in spray front velocity and penetration depth. The stationary air entrainment, however, is only moderately increased as is the total amount of captured air, since the fuel vapour displaces air in the spray.

Optical investigation of flash boiling and its effect on in-cylinder combustion for butanol isomers andiso-octane

“…To the best of author's knowledge, such a link between flash boiling spray and in-cylinder combustion is relatively rare in open literature. [52][53][54][55][56][57] Soot emission in terms of natural flame luminosity was estimated using high-speed imaging inside an optically accessible engine.…”

Ultra-high speed X-ray imaging of dynamic fracturing in cementitious materials under impact

“…Given the polychromatic beam spectrum with a peak energy of around 30-40 keV, the propagation based interference between transmitted X-rays results in an increased contrast of material edges while preserving the material geometrical representation by keeping the fringe effect well within the subpixel is captured within each radiograph providing the ability to study various transient dynamic phenomena in both solids and liquids within a representative volume scale (e.g. [17][18][19]).…”

Experimental assessment of the rotor outlet flow in a twin-entry radial turbine by means of Laser Doppler Anemometry

“…The LDA technique has been used for many applications as analysing the influence of superheated injection on liquid and gaseous flow field of an experimental single-hole gasoline direct injection injector in Bornschlegel et al 21 or validating numerical simulations as Kumar et al 22 for cavitating flow in a multi-hole diesel fuel injector or Theile et al 23 for the influence of early fuel injection on charge motion in a direct injection spark ignition engine. Grosjean et al 24 and Fischer 25 studied the suitability of this technique for measuring velocity fields and particles concentration in comparison with other techniques.…”