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Abstract

The alarming rise in global greenhouse gas concentrations poses a serious threat to the Earth’s ecosystems and, as a consequence, many scientists worldwide are striving to combat climate change. However, implementing green transitions remains particularly challenging in certain sectors. For instance, no electrification strategies are currently available for medium- and large-scale Diesel engines. A partial substitution of Diesel with high-octane fuels represents the only practical and immediate solution. In particular, Dual-Fuel Internal Combustion Engines (DFICEs) have demonstrated significant reductions in soot and CO2 emissions. Nonetheless, cavitation, and specifically cavitationinduced erosion, can be strongly influenced by fuel properties and operating conditions.

Current state-of-the-art studies on cavitation and cavitation-induced erosion often rely on simplified thermodynamic equations of state (EoS), such as barotropic EoS, which rarely account for thermal effects. This limitation may hinder accurate analysis, particularly when comparing fuels that are strongly influenced by thermodynamic properties. The present work addresses this gap by examining pressure peaks and thermal effects during the collapse of a vaporous cavitating cloud using real-fluid thermodynamics. The closure of the numerical framework is achieved through a structured table that linearly reconstructs the thermodynamic properties of the working fluid based on the PC-SAFT EoS. Compared to solving complex EoS directly or employing unstructured finite-element-based tables, this structured database proves more efficient, with search speed independent of the table resolution.

The tabulated EoS has been incorporated into an explicit density-based solver within OpenFOAM V7. OpenFOAM (Open Source Field Operation And Manipulation) is a powerful, free, and open-source computational continuum mechanics (CCM) C++ toolbox that primarily focuses on Computational Fluid Dynamics (CFD). Given the broad range of velocity and sound-speed values encountered in such simulations, a Mach-consistent numerical flux capable of handling subsonic to supersonic flow conditions has been implemented.

For the first time, real-fluid thermodynamics have been applied to study both the collapse of vaporous bubble clusters and injector flow simulations. Particular attention is devoted to cavitation near walls, enabling the sampling of both pressure peaks and thermal effects. This work contributes to a deeper understanding of cavitation phenomena and highlights how fuel properties influence cavitation-induced erosion and jet quality in injectors.

Building on previous contributions [Fathi et al., 2022, Matheis and Hickel, 2017], we propose a numerical framework that incorporates a multiphase large-eddy Eulerian model combined with Peng-Robinson (RP) EoS/Redlich-Kwong-Peng-Robinson (RKPR) EoS and Vapour Liquid Equilibrium (VLE) calculations. Our extended framework integrates internal nozzle flow, spray development, cavitation, and needle dynamics. Key advancements include the incorporation of the PC-SAFT EoS, the VT-flash algorithm [Vidal et al., 2020], the IB Method [Stavropoulos Vasilakis et al., 2019], and entropy-scaling techniques into the flow solver. Importantly, this framework maintains a tuningparameter-free approach, recognising the challenges associated with property measurements of novel fuel blends.

Implemented in the widely adopted open-source CFD solver OpenFOAM V7, this advanced modelling strategy ensures enhanced robustness and reliability. The solver has been tested and used for bubble collapse dynamics, where extreme gradients are in place, as well as for injector flows. The scope of the project referred to dual-fuel engines also owing to the overarching objectives set by the MSCA DN. However, given the high range of validation cases performed on this solver, we are confident that the solver could be applied to any jet/spray flow with high velocities, temperatures and or pressure, such as turbomachinery flows, flows in components of materialising thermo-dynamic cycles, as well as other types of industrial nozzles, e.g. for spray cooling. The solver can work well for any kind of flow involving cavitation and high pressure or velocity gradients. And it is particularly suited for injector flows under high-pressure and high-temperature conditions. Validation has been performed on the benchmark Spray C and Spray D cases, supported by an extensive cross-validated database. Ultimately, the proposed methodology delivers accuracy and robustness comparable to commercial software, without requiring parameter tuning.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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