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The flow mechanism of internal two-phase flow atomization remains unclear despite its widespread applications. A newly outside-in-liquid (OIL) atomizer is designed to investigate the two-phase flow mechanism inside the effervescent atomizer in this work. Numerical simulation is used to study the internal flow characteristics of the OIL atomizer under different gas–liquid mass flow ratios (GLRs). The findings indicate that the volume-of-fluid (VOF) model and compressible Euler method effectively capture the intricate evolution of the internal flow. The cavitation phenomenon occurs before the gas phase reaching the orifice. Subsequently, the cavitation phenomenon disappears as the gas phase flows downstream into the orifice. At different GLRs, the gas phase before reaching the mixing chamber is a single separated bubble. However, the final flow patterns are mainly annular flow, which is most obvious at high GLR. Increasing the GLR can increase the gas void fraction in the orifice. Furthermore, the gas void fraction will reach the peak faster and then remain stable. The two phases are accelerated after entering the orifice. Among them, the flow velocity of gas phase is much higher than that of liquid phase. This research demonstrates the notable impact of GLR on the internal flow. Furthermore, it addresses the existing research gap in this aspect of internal flow. [ABSTRACT FROM AUTHOR]

The substantial demand for enhanced combustion efficiency and achieving near-zero emissions in GDI engines has spurred the introduction of a novel approach employing elliptical divergent nozzle spray technology. This innovative method, which marries the elliptical shape with a divergent nozzle, not only elevates downstream atomization quality but also mitigates nozzle tip wetting. Nevertheless, there exists a dearth of documented research regarding the internal flow and outflow characteristics related to the atomization potential of elliptical divergent nozzles. Numerical investigations have been carried out to scrutinize alterations in the three-dimensional cavitation morphology, the dispersion of turbulent vortex structures, and the nozzle exit flow parameters across a range of cavitation number conditions for both circular and elliptical divergent nozzles. The research findings demonstrate that the cavitation intensity of the elliptical divergent nozzle consistently surpasses that of the circular divergent nozzle. Also, the elliptical divergent nozzle consistently exhibits a greater number of turbulent vortex structures compared to the circular divergent nozzle across all cavitation number conditions. Additionally, as the cavitation number decreases, the difference in turbulence vorticity magnitude between the exits of the circular and elliptical divergent nozzles gradually increases. Furthermore, the elliptical diverging orifices are more susceptible to cavitation compared to their circular counterparts. The elliptical divergent nozzle outperforms the circular nozzle with a substantial 24.6% increase in exit velocity, especially at a cavitation number of 1.016. [ABSTRACT FROM AUTHOR]

The internal flow in nozzle and macroscopic spray characteristics of diesel and biodiesel, by employing a validated numerical model and a laser-based Mie-scattering technique, are investigated. The results indicate that both the mass flow rate and the orifice exit average velocity of diesel are larger than those of biodiesel. Also, that diesel consistently produced higher cavitation intensity and turbulence kinetic energy confirms diesel can boost the naissance of cavitation and the turbulence disturbance inside the nozzle. Meanwhile, the cavitation intensity and the turbulence kinetic energy increase dramatically as the injection pressure increases; the cavitation domain is consistent with the domain of high turbulence kinetic energy. Furthermore, the radial velocity of diesel is significantly higher than biodiesel under the same injection pressure, while the radial velocities of both fuels increase as the injection pressure increase. Moreover, the spray tip penetration of biodiesel is longer than that of diesel, while the aerodynamic spray cone angle of biodiesel is narrower that of diesel under the same injection pressure. Higher surface tension and viscosity of biodiesel resulted in smaller cavitation intensity, turbulence kinetic energy and radial velocity at the nozzle exit, which in turn contribute to the narrowing of the aerodynamic spray cone angle. [ABSTRACT FROM AUTHOR]

The non-circular orifice has potential ability to increase the fuel spray and mixing quality. While the application of non-circular orifice in the GDI injection system hasn't been reported yet. The inner flow behaviors have great impact on the spray and mixing quality. Therefore, Volume of Fluid (VOF) and Large Eddy Simulation (LES) method are introduced to investigate the effects of non-circular orifices cross section shapes of GDI injector on the inner flow patterns and nozzle exit flow parameters. From the results, the total vapor phase volume fraction of the elliptical orifice is smaller than that in the circular one. The vapor phase fraction of elliptical orifice decreases with the increase of aspect ratio, and the vapor phase volume fraction of the elliptical E4 orifice is the smallest. In addition, the critical cavitation point of circular orifice is earlier than that of elliptical orifice, which indicated that the circular orifice is more prone to cavitate than the elliptical one. Finally, the discharge coefficient of circular orifice is the smallest among all orifices. The velocity coefficient of elliptical E4 orifice is the minimum under the cavitation conditions, while the elliptical E4 orifice held the largest area coefficient among other orifices. [ABSTRACT FROM AUTHOR]

The nozzle orifice geometry has great impact on the internal flow and spray characteristics, and thus affects the fuel-air mixture quality for diesel engines. This paper presents experimental and numerical research on the internal flow and spray behaviors with biodiesel for elliptical orifice with large aspect ratio and circular orifice of diesel nozzles, under high injection pressure and backpressure conditions. Large Eddy Simulation (LES) and Schnerr and Sauer cavitation model were adopted to study the internal flow, and the numerical models were validated firstly in terms of the mass flow rate, center line pressure and cavitation morphology. The elliptical spray images at the minor and major planes were acquired simultaneously with two CCD cameras through shadowgraph method. The results showed that the discharge coefficient of elliptical orifice was higher than that of circular orifice, which indicated that the elliptical orifice has better flow performance as compared to circular orifice. In addition, the vapor volume fraction at the circular orifice exit was larger than that of elliptical orifice, while the vorticity magnitudes were consistent lower than that of elliptical nozzle at the same injection pressure. And also, the elliptical orifice has more turbulence vortex structures near the nozzle exit than that of circular orifice, and the number of turbulence vortex structures increased as the injection pressure increases. Moreover, the cavitation distribution in the elliptical orifice in the direction of major axis shows longer length than that in the minor axis direction. The cavitation morphology at the elliptical orifice exit showed a unique horseshoe shape, while the cavitation morphology for circular orifice was still distributed symmetrically. Another important point is that the cavitation domain was similar with distribution of the turbulence vortex structures. Furthermore, the variation trend of elliptic spray cone angle proved that the elliptical spray underwent axis-switching even under high injection pressure and backpressure. Finally, the circular orifice spray held longer spray tip penetration in comparison to elliptical spray, while the elliptical exhibited much larger spray cone angle in all view planes. Because the elliptical spray underwent greater air dynamic drag induced by larger spray surface area. And the higher vorticity magnitude and more turbulence vortex structures at the elliptical orifice exit could also promote the initial spray breakup and thus inhibit the development of spray tip penetration. The axis-switching of elliptical spray can also increase the air entrainment ratio, which was conductive to increase the spray cone angle. [ABSTRACT FROM AUTHOR]

• The cavitation intensity and vorticity magnitude of ethanol is smaller than gasoline. • The swallowtail-like spray structure only appeared in the major view plane for gasoline spray. • Using ethanol can inhibit the formation of swallowtail-like spray structure. • The gasoline spray tip branching angle increased with the increase of back pressure. Alternative fuels have significant effects on the nozzle inner flow and spray behaviors. The present research works focus on the gasoline and ethanol impact the inner flow and spray behaviors with elliptical GDI injector. The inner flow patterns were performed with numerical modeling method, while the spray characteristics were measured by high-speed shadowgraph technique. Results indicated that the cavitation intensity of ethanol is smaller than that of gasoline, while the mass flow rate of ethanol is higher than gasoline. Also, the gasoline is giving more turbulence vortex structures in the minor axis direction of elliptical GDI injector and higher vorticity magnitude at nozzle exit compared to ethanol. The nozzle exit velocity for gasoline is consistent higher than ethanol. Additionally, the unique swallowtail-like spray structure discharging from elliptical GDI injector for gasoline only appeared in the major view plane. However, this unique spray structure did not appear in the spray tip with ethanol. Finally, gasoline spray tip penetration and spray cone angle are larger than that of ethanol spray, and the spray tip branching angle increased with the increase of back pressure for gasoline spray. [ABSTRACT FROM AUTHOR]

The application of non-circular elliptical orifice is recognized to increase the fuel spray and mixing quality, which has potential ability for modern gasoline direct injection (GDI) engines. In this research work, a single-hole elliptical GDI injector with aspect ratio of 4 was adopted. Numerical simulation and experimental spray test are both introduced to study the inner flow patterns and spray characteristics. The results indicated that the cavitation is mainly distributed on the minor axial plane of the elliptical GDI injector, and the cavitation domain decreases gradually with the increase of back pressure. Additionally, the unique swallowtail-like spray structure discharging from the elliptical GDI injector with aspect ratio of 4 was captured for the first time, and the swallowtail-like spray structure only appeared on the major view plane of the elliptic spray. Moreover, the GDI elliptical spray tip branching length reduced with the increase of the back pressure, and the high back pressure can inhibit the formation of swallowtail-like spray structure. Finally, the branching angle at the spray tip increased with the increase of back pressure, because high back pressure will enhance the effect of high aerodynamic force. • The swallowtail-like spray structure was captured in the major view plane. • The spray tip branching length reduced with the increase of the back pressure. • High back pressure can inhibit the formation of swallowtail-like spray structure. • The spray tip branching Angle increased with the increase of back pressure. [ABSTRACT FROM AUTHOR]