Abstract
In the optimization of GDI engines, fuel injection plays a crucial role since it can affect the combustion process and, thus, fuel efficiency and pollutant emissions. The challenging task is to obtain the required fuel distribution and atomization inside the combustion chamber over a wide range of engine operating conditions. To achieve such goals, flash-boiling can be exploited. Flash-boiling is a phenomenon occurring when fuel temperature exceeds saturation temperature or, similarly, when ambient pressure is lower than saturation one. Under these conditions, which can occur inside the injector or directly in the combustion chamber, the fuel undergoes extremely accelerated breakup and quickly evaporates. The proposed manuscript shows the application of an alternative flashboiling model, recently implemented by Siemens-PLM in STAR-CD V.2019.1, to be applied in 3D-CFD Lagrangian simulations of GDI sprays. Results are validated against experimental data, provided by the SprayLAB of the University of Perugia, on a single-hole research injector. The new flash-boiling model consists of three main parts: an atomization model able to compute droplet initial conditions and the overall spray cone angle; an evaporation model and, finally, a droplet break-up model; the last two models are designed to simulate all the physical events occurring when droplets are injected into the combustion chamber. As for the investigated operating condition, vessel pressure and temperature are 40 kPa and 293K, respectively; as for the fuel (n-Heptane) temperature, it ranges from 303.15 K to 393.15 K, on equal injection pressure (10 MPa). The numerical-experimental comparison is carried out in terms of liquid penetration, imaging, and droplet sizing.
Highlights
In the last decade, besides the increasing level of hybridization [1], many efforts have been dedicated to increase the efficiency of the internal combustion engine while decreasing tailpipe emissions
The new flash-boiling model consists of three main parts: an atomization model able to compute droplet initial conditions and the overall spray cone angle; an evaporation model and, a droplet break-up model; the last two models are designed to simulate all the physical events occurring when droplets are injected into the combustion chamber
Since the internal nozzle geometry was not available for the investigated injector, an alternative approach developed at the SprayLAB of the University of Perugia was exploited, which is based on experimental momentum measurements as described in [4243]
Summary
Besides the increasing level of hybridization [1], many efforts have been dedicated to increase the efficiency of the internal combustion engine while decreasing tailpipe emissions. In this panorama, a crucial role is played by CFD analyses which allow to reduce time- and cost-to-market thanks to a proper prediction of the knock onset. To promote break-up and, evaporation of the spray, injection can be carried out under flash boiling conditions
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