3D-CFD Simulation of a GDI Injector Under Standard and Flashing Conditions

Sparacino, Simone; Berni, Fabio; Riccardi, Marco; Cavicchi, Andrea; Postrioti, Lucio

doi:10.1051/e3sconf/202019706002

Cited by 5 publications

(3 citation statements)

References 38 publications

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“…As discussed in the introduction, so far, most numerical analyses on FII are based on one-dimensional approaches and have clear limitations. Although there are many reports on various flashing simulations, e.g., flash atomization [30][31][32], internal nozzle flows [33][34][35][36], and leakage [37,38], CFD modeling of FII is scarce. The present study aims at exploring the transient flow behavior during the FII by means of CFD simulations.…”

Section: Methodsmentioning

confidence: 99%

CFD Modeling of Phase Change during the Flashing-Induced Instability in a Natural Circulation Circuit

Liao

Lucas

2023

Processes

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Flashing-induced instability (FII) has a significant impact on the safe operation of a natural circulation circuit, a phenomenon frequently encountered in the cooling systems of advanced light water reactors. While one-dimensional system codes are commonly used for the engineering design and safety analysis of FII, there is a strong academic interest in understanding the underlying physical mechanisms. To address this, high-resolution computational fluid dynamics (CFD) simulations serve as a valuable tool. However, the current state of CFD modeling for two-phase flows with phase change, which are particularly highly transient fluctuating flashing flows, is still in its early stages of development. In this study, we establish a CFD model that focuses on interphase heat transfer to analyze the phase change during FII. By incorporating experimental data from the literature, we investigate the transient flow field and thermodynamic behavior in the riser of the GENEVA test facility. The study provides valuable insights into the non-equilibrium and interfacial transfer phenomena during the phase change as well as the effect of high-frequency fluctuation. Additionally, we discuss in detail the challenges associated with FII modeling and the limitations of the current model. We also provide suggestions for potential improvements in future numerical studies. The results show that the thermal phase change and heat transfer coefficient model adopted for the simulation reasonably captures the evaporation and condensation process. However, it tends to under-predict the evaporation rate, which results in a larger pressure drop through the riser. The observation that the void fraction close to the wall is higher than that in the riser center evidences that the reliable modeling of bubble size distribution as well as the inclusion of non-drag forces are important for predicting the transverse void distribution. Furthermore, it reveals that both the temperature and pressure change in an FII, and their effects on phase change should be taken into account simultaneously.

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Section: Methodsmentioning

confidence: 99%

CFD Modeling of Phase Change during the Flashing-Induced Instability in a Natural Circulation Circuit

Liao

Lucas

2023

Processes

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“…For turbulence modelling, a k-ε RNG is adopted given the successful application in similar studies [31][32]. Droplets are initialized following the approach proposed in [33][34] [35] whereas the spray break-up is modelled with Reitz-Diwakar's [36] model and the droplet-wall interaction with Senda's model [37]. Heat transfer is modeled using a recently improved version of the GruMo-Unimore heat transfer model [38][39] [40], which has proven to be successful in a wide range of engine applications [41].…”

Section: D-cfd Simulation General Setupmentioning

confidence: 99%

Effect of Lagrangian-phase Modelling on Charge Stratification and Spatial Distribution of Threshold Soot Index for Toluene Reference Fuel Surrogates

Pessina

Borghi

2021

E3S Web Conf.

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Nowadays, soot emissions are one of the major concerns in Direct Injection Spark Ignition engines. Soot prediction models can be computationally expensive, especially when particle mass, number, and size distribution are to be forecast. While soot formation heavily depends on the chemical and physical characteristics of the fuel, the simulation of the exact composition of a real gasoline is computationally unfeasible. Thus, it is essential to find simplified yet representative pathways to reduce the computational cost of the simulations. On the one hand, the a-priori investigation of the factors influencing particulate onset can be a simplified approach to compare different solutions and strategies with much cheaper costs than the modelling of soot formation and oxidation mechanisms. On the other hand, the use of surrogate fuels is a practical approach to cope with the fuel chemical nature. Although they poorly mimic the evaporation properties of a real gasoline, Toluene Reference Fuels are broadly adopted to match combustion relevant properties of the real fuels. In this study, the spatial distribution of the Threshold Soot Index in the fluid domain is investigated for three surrogates characterized by an increasing content of toluene (0 mol%, 30 mol%, 60 mol%). The correlation between the sooting tendency and the fuel distribution in the combustion chamber before spark ignition time can provide useful preliminary indications, without spending the computational effort of the whole soot model multicycle resolution. In particular, two approaches for the lagrangian description of the injected fuel are investigated: a multicomponent approach and a single component one, this last driven by a high-fidelity lumped modelling of the surrogate properties for both liquid and vapor phase.

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“…As for the initial velocity, it is calculated from the velocity coefficient, which in turn corresponds to the ratio between discharge and area coefficients. Further details on the droplet initialization based on the hydraulic coefficients can be found in [49,50]. The semi-cone angle is fixed to nearly 5° for all the injectors.…”

Section: Analysed Injectors and Condition Numerical Setupmentioning

confidence: 99%

A 3D-CFD numerical framework for the simulation of both light- and heavy-duty Diesel injectors

Sparacino

Borghi

2021

E3S Web Conf.

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In spite of the effort of the engine manufacturers to improve exhaust aftertreatment efficiency, thus reducing tailpipe pollutants, the unaffordable tightening of the laws dealing with emissions puts a strain on the use of Diesel engines for passenger cars in the next decades. However, for trucks and marine applications, such technology may remain the predominant solution all over the world. For this reason, development of heavy-duty Diesel engines goes on and Computational Fluid Dynamics (CFD) can play a crucial role in supporting designers. Among the different goals of the numerical analyses on Diesel engines, 3D-CFD Lagrangian simulations can be adopted to optimize fuel injection, which is a crucial aspects as able to affect both combustion efficiency and emissions. For this purpose, a robust numerical framework is needed. The present work aims at proving that models suitable for the simulation of light-duty Diesel injectors can be proficiently extended for heavy-duty ones. In particular, attention is here focused on droplet break-up. An alternative secondary break-up model is proposed. It is purposely calibrated on the well-known Spray A injector provided by the Engine Combustion Network (ECN), which can be assumed as representative of injectors for light-duty applications. 3D-CFD simulations are validated against experimental data in terms of both liquid and vapour penetrations and imaging. Then, the numerical set-up adopted for the Spray A is employed without any further adhoc tuning to investigate Spray C and Spray D which can be considered, instead, representative of heavy-duty nozzles. The proposed model proves to be effective for the prediction of the break-up rate. All the injectors are tested via vessel simulations characterized by the same ambient pressure and temperature, equal to 6 MPa and 900 K respectively. Even the adopted fuel is common, namely n-Dodecane, whose injection pressure and temperature are fixed to 150 MPa and 363 K, respectively.

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3D-CFD Simulation of a GDI Injector Under Standard and Flashing Conditions

Cited by 5 publications

References 38 publications

CFD Modeling of Phase Change during the Flashing-Induced Instability in a Natural Circulation Circuit

CFD Modeling of Phase Change during the Flashing-Induced Instability in a Natural Circulation Circuit

Effect of Lagrangian-phase Modelling on Charge Stratification and Spatial Distribution of Threshold Soot Index for Toluene Reference Fuel Surrogates

A 3D-CFD numerical framework for the simulation of both light- and heavy-duty Diesel injectors

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