Flashboiling-induced targeting changes in gasoline direct injection sprays

Abstract

By definition, flashboiling is referred to as superheated injections. The sudden occurrence of boiling inside the fuel can change the spray structure dramatically. Up to 99% of all injection processes during the New European Driving Cycle and 95% during 'Real Driving Emissions' tests are, with respect to mid-range cars, in a state of thermodynamic nonequilibrium below the specific vapor pressure of gasoline. Considering this fact, the scientific question is not the appearance of flashboiling during the operation of stoichiometric homogeneous charge direct injection gasoline engines but the intensity of occurring spray processes and their influence on nominal spray designs. As a consequence of induced targeting changes, the positive influence of flashboiling on the droplet size distribution and the penetration depth can be counteracted. As main driving factors for targeting changes, jet-to-jet interactions can be identified. By applying appropriate nozzle design features, the potential of flashboiling can be exploited and the targeting changes of the nominal spray designs, considered negatively, are avoided mostly. This work focuses on flashboiling-induced targeting changes, the socalled phenomenon of ''spray collapse'': its root cause, development and avoidance.

3D mapping of droplet Sauter mean diameter in sprays

“…This confirms that a contraction of the whole spray results also under the studied injection conditions due to the spray-induced lowpressure field between these jets. This spray contraction would be even stronger for very low ambient pressure conditions (less than 0.1 MPa) that support flash-boiling [44,46]. Furthermore, in planes X= 50 mm and X=60 mm the position and the shape of the vortices is visible.…”

Prediction of spray collapse in multi-hole gasoline direct-injection fuel injectors

“…A broad consensus among several of these studies is that an increase in the momentum transfer between the ambient gas and fuel results in plume-to-plume interaction, which subsequently leads to the collapse of the spray. 13,21,22 Recently, Sphicas et al 23 reaffirmed this observation based from their studies on inter-plume aerodynamics in an eight-hole GDI injector.…”

12th International Congress of Engine Combustion Processes: Current problems and modern techniques (ENCOM2015)

“…Exhaust condensate may be used to be additionally injected and thus to realize an engine concept with dual DI. Also related to the DISI process, Kra¨mer et al 6 had investigated the flashboiling-induced targeting changes in the sprays (''spray collapse'')-its root cause, development and avoidance. They show in a general survey that flashboiling and the jet-to-jet interaction do not mean the same as it is often used in the literature.…”