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Research Papers: Internal Combustion Engines

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

[+] Author and Article Information
Jun Ishimoto1

Institute of Fluid Science, Tohoku University, Sendai 980-8577, Japanishimoto@alba.ifs.tohoku.ac.jp

Fuminori Sato, Gaku Sato

 KEIHIN Co., Tochigi R&D Center, 2021-8 Hoshakuji, Takanezawa-machi, Shioya-Gun, Tochigi 329-1233, Japan

1

Corresponding author.

J. Eng. Gas Turbines Power 132(8), 082801 (May 20, 2010) (15 pages) doi:10.1115/1.4000264 History: Received February 24, 2009; Revised August 24, 2009; Published May 20, 2010; Online May 20, 2010

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.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Overview of the computational system employed by the present calculation

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Figure 2

Computational system for injector nozzle

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Figure 3

Overview of the instantaneous isocontour of an actual cavity fraction (vapor-phase fraction) αγ along with the liquid-vapor phase volume fraction of α=0.5. The color graduation represents the scalar magnitude of cavity fraction αγ.

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Figure 4

Close-up view of the instantaneous isocontour of the actual cavity fraction (vapor-phase fraction) αγ along with the liquid-vapor phase volume fraction of α=0.5. The color graduation represents the scalar magnitude of cavity fraction αγ.

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Figure 5

Instantaneous velocity vector v profiles on the isosurface of α=0.5 just downstream of the nozzle aperture

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Figure 6

Instantaneous velocity vector v profiles on the isocontour of αγ around the vicinity of the cavity generated region

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Figure 8

Characteristic atomizing spray behavior in comparison with results of models with and without cavitation under primary breakup at an initial unsteady condition (t=4.1×10−4 s)

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Figure 9

Characteristic atomizing spray behavior in comparison with results of models with and without cavitation under primary breakup at a quasi-steady condition (t=8.5×10−4 s)

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Figure 10

Instantaneous isosurface of enstrophy E profiles just inside and downstream of the nozzle with scalar magnitude of vorticity |ω|

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Figure 11

Instantaneous isosurface of the second invariant of velocity gradient tensor Q profiles just inside and downstream of the nozzle with scalar magnitude of vorticity |ω| (with cavitation model)

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Figure 13

Statistical result for the frequency of the droplet diameter distribution fD as a function of streamwise coordinate (−y) and droplet diameter Dp at all integrated time steps. The threshold of fixed value α is α=0.1.

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Figure 14

Schematic of the statistical analysis of frequency of droplet diameter profile

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Figure 12

Instantaneous isosurface of the second invariant of velocity gradient tensor Q profiles just inside and downstream of the nozzle with scalar magnitude of vorticity |ω| (without cavitation model)

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Figure 7

Characteristics of the potential core of the lateral injector nozzle flow just downstream of the nozzle aperture outlet

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