String Cavitation in a Fuel Injector

Three-dimensional flow structure and string cavitation in a fuel injector and their effects on discharged liquid jet

“…However, experimental investigations [12][13][14] carried out with multi-hole fuel injectors have revealed the existence of another kind of cavitation in the sac, which is commonly called string cavitation, owing to their thin, filament-like appearances. The discovery of string cavitation existence is important, as it has been proven that string cavitation has a greater influence on spray angle [15][16][17] compared to the film-like geometrical cavitation in the nozzle. Moreover, the existence of string cavitation also reveals the complex flow structure inside the sac of multi-hole fuel injectors.…”

“…This complex flow structure is mainly caused by the interactions between the nozzle holes 14,15 as well as needle eccentricity and needle lift on the internal flow of the sac. [17][18][19][20][21][22][23] The effects of needle lift and needle eccentricity on string cavitation existence are particularly important. For asymmetric single-hole fuel injectors (where the interactions between nozzle holes are non-existent), it is possible for string cavitation to occur under eccentric sac/needle configuration 15,17,21,22 at low needle lift.…”

“…[17][18][19][20][21][22][23] The effects of needle lift and needle eccentricity on string cavitation existence are particularly important. For asymmetric single-hole fuel injectors (where the interactions between nozzle holes are non-existent), it is possible for string cavitation to occur under eccentric sac/needle configuration 15,17,21,22 at low needle lift. This tendency of string cavitation to occur in the sac under low needle lift condition has been documented by various studies, [16][17][18]20,23,24 but the mechanism behind its occurrence is still unclear.…”

“…For asymmetric single-hole fuel injectors (where the interactions between nozzle holes are non-existent), it is possible for string cavitation to occur under eccentric sac/needle configuration 15,17,21,22 at low needle lift. This tendency of string cavitation to occur in the sac under low needle lift condition has been documented by various studies, [16][17][18]20,23,24 but the mechanism behind its occurrence is still unclear. Although it is strongly indicated that string cavitation occurrence is caused by strong vortex ring flow in the sac, accurate measurement of the three-dimensional (3D) velocity field in the sac has not been available yet.…”

“…This is because of the difficulties associated with visualization of internal flow in diesel injectors, such as the small sac size and very fast flow velocity. As a substitute, studies have turned to either using numerical simulation to explain about the origin of string cavitation 17,18,23,25 or carry out twodimensional (2D) particle image velocimetry (PIV). 16,20 This study aims to reveal the mechanism behind string cavitation occurrence at low needle lift.…”