Computational Prediction of the Effect of Microcavitation on an Atomization Mechanism in a Gasoline Injector Nozzle

Abstract

The effect of microcavitation on the 3D structure of the liquid atomization process in a gasoline injector nozzle was numerically investigated and visualized by a new integrated computational fluid dynamics (CFD) technique for application in the automobile industry. The present CFD analysis focused on the primary breakup phenomenon of liquid atomization which is closely related to microcavitation, the consecutive formation of liquid film, and the generation of droplets by a lateral flow in the outlet section of the nozzle. Governing equations for a high-speed lateral atomizing injector nozzle flow taking into account the microcavitation generation based on the barotropic large eddy simulation-volume of fluid model in conjunction with the continuum surface force model were developed, and then an integrated parallel computation was performed to clarify the detailed atomization process coincident with the microcavitation of a high-speed nozzle flow. Furthermore, data on such factors as the volume fraction of microcavities, atomization length, liquid core shapes, droplet-size distribution, spray angle, and droplet velocity profiles, which are difficult to confirm by experiment, were acquired. According to the present analysis, the atomization rate and the droplets-gas atomizing flow characteristics were found to be controlled by the generation of microcavitation coincident with the primary breakup caused by the turbulence perturbation upstream of the injector nozzle, hydrodynamic instabilities at the gas-liquid interface, and shear stresses between the liquid core and periphery of the jet. Furthermore, it was found that the energy of vorticity close to the gas-liquid interface was converted to energy for microcavity generation or droplet atomization.

Large-eddy simulation of cavitating nozzle flow and primary jet break-up

“…In their simulations of cavitating nozzle flows, a free gas content was considered, but effects on the primary jet break-up were not assessed. Ishimoto et al 51 performed the first fully coupled simulation of cavitating nozzle flow and jet break-up with a fully compressible, barotropic LES model based on a VOF method.…”

Numerical simulation of spray break-up from cavitating nozzle flow by combined Eulerian–Eulerian and volume-of-fluid methods

“…While in Ref. [10] the model was validated on the well-documented water nozzle experiments from Sou et al [11], and Bicer and Sou [12], the current work shows the simulation of the simplified low-pressure gasoline injector reported by Ishimoto et al [4]. The presented simulation is performed on a finer computational grid, since the highest mesh resolution is D / 72 compared to D / 56 in Ref.…”

“…The simulated case is based on the publication of Ishimoto et al [4] showing a simplified gasoline injector with a short-length nozzle of L = 60 μm and D = 226 μm. Three phases have been defined, and the fluid properties are listed in Fig.…”

“…Only few numerical studies of the liquid break-up with surface-capturing methods by taking into account cavitating nozzle flow have been published in the literature. A pioneer work is reported by Ishimoto et al [4], who applied VOF and Large Eddy Simulation (LES) for a simplified industrial gasoline injector with cavitation in the nozzle. In this work the three phases, liquid, vapor and gas, are treated like two phases by considering liquid-vapor as cavitating mixture.…”

“…The presented simulation is performed on a finer computational grid, since the highest mesh resolution is D / 72 compared to D / 56 in Ref. [4]. This leads to five times more computational cells.…”