Real-fluid simulation of ammonia cavitation in a heavy-duty fuel injector

The reduction of greenhouse gases (GHG) emitted into the earth's atmosphere, such as carbon dioxide, has obviously become a priority. Replacing fossil fuels with cleaner renewable fuels (such as ammonia) in internal combustion engines for heavy-duty vehicles is one promising solution to reduce GHG emissions. This paper aims to study the cavitation formation in a heavy-duty injector using ammonia as fuel. The simulation is carried out using a fully compressible two-phase multi-component real-fluid model (RFM) developed in the CONVERGE CFD solver. In the RFM model, the thermodynamic and transport properties are stored in a table which is used during the run-time. The thermodynamic table is generated using the in-house Carnot thermodynamic library based on vapor-liquid equilibrium calculations coupled with a real-fluid equation of state. The RFM model allows to consider the effects of the dissolved non-condensable gas such as nitrogen on the phase change process. The obtained numerical results have confirmed that the model can tackle the phase transition phenomenon under the considered conditions. In contrast to previous numerical studies of the cavitation phenomenon using hydrocarbon fuels, the formed cavitation pockets were found to be primarily composed of ammonia vapor due to its high vapor pressure, with minimal contribution of the dissolved non-condensable nitrogen.Comment: 32nd European Conference on Liquid Atomization & Spray Systems, ILASS Europe, Sep 2023, Napoli, Ital

Propulsive Performance for an Oscillating Airfoil Applied to Mini Air Vehicles

In the present work, the optimal control to maximize the energy harvesting through a sinusoidal vertical gust profile is investigated through 2D URANS simulations and wind tunnel tests of NACA 0015 wing. The control is defined by a harmonic pitching motion of the wing, with the main objective to determine the optimal control parameters represented by the optimal pitch amplitude and phase shift that maximize the energy harvesting efficiency. The computational fluid dynamics (CFD) based on the k-omega -SST turbulence model is implemented to find the optimal control parameters for a simultaneously heaving and pitching 2D wing. For the experimental investigation, a wind tunnel model is manufactured and used to perform the wind tunnel tests to prove the energy harvesting concept and validate the obtained CFD results. Since it wasn't feasible to generate sinusoidal vertical gust in the wind tunnel, the gust effect is modeled by a sinusoidal heaving motion of the wing. A robotic arm is used to perform the simultaneous heaving and pitching motions of the wing. The numerical results showed the significant effect of the control activation to increase the energy harvesting where an optimal efficiency of 67 % is achieved at a gust amplitude of 0,5 m/s and frequency of 0,4 Hz. It was also found that an increase in the amplitude of the sinusoidal gust profile brings significant increment in the amount of energy harvested. Wind tunnel tests proved the concept of energy harvesting and exhibit the same trends of efficiency variation with pitch amplitude as that obtained through the numerical simulations. The obtained results showed that the energy harvesting flight technique is very promising regarding the improvement of the performance of mini-UAVs

Modélisation de la rupture, du changement de phase et du mélange d'un jet de double carburant

The recent stringent emissions legislation poses new challenges to the continued use of diesel-powered internal combustion engines due to their carbon dioxide emissions and urban pollution, which accelerate climate change and are linked to severe health problems, respectively. Dual-fuel internal combustion engines (DFICE) using alternative renewable fuels are among the promising concepts for reducing pollutant emissions in applications where electrification is not considered a feasible solution to the emissions problem, such as cargo ships and heavy-duty trucks. The effective design of the fuel injection equipment (FIE) is considered a key priority for the industrial development of the DFICEs. Thus, advanced design and simulation tools are required to achieve better designs of such dual-fuel systems. Accordingly, the main objective of the current thesis is to develop a predictive and efficient CFD model for multi-component two-phase flow simulations in the context of DFICE employing renewable fuels such as methanol or ammonia under different thermodynamic (sub- and super-critical) regimes, allowing an automatic/smooth transition between these regimes that can coexist during the fuel injection and mixing events. More specifically, the current work proposes a fully compressible multi-component two-phase real-fluid model (RFM) with a diffused interface and closed by a thermodynamic equilibrium tabulation method based on various real-fluid equations of state (EoSs). The proposed real-fluid thermodynamic tabulation approach can further handle ternary systems in addition to binary systems. The thermodynamic table is generated using the in-house Carnot thermodynamic library, which performs the vapor-liquid equilibrium (VLE) calculation using a robust isothermal-isobaric (TPn) flash coupled to various real-fluid EoSs. The proposed model is first applied to investigate the phase change and mixing processes of a single n-dodecane droplet in a bi-component environment composed of nitrogen and methanol at high pressure, mimicking a dual-fuel configuration using highly resolved simulations. Next, to address high-pressure fuel injection, a real fluid atomization model is proposed, in which the RFM model is coupled to a subgrid-scale (SGS) model, employing a surface density approach to model fuel atomization within the LES framework. The Engine Combustion Network (ECN) Spray A injector is used as a reference for the proposed model validation. The obtained numerical results have shown good agreement with the various ECN experimental data. Besides, a parametric variation of the ECN Spray A conditions has shown the capability of the RFM model to well predict the experimental variations of the spray characteristics. Following the model validation, the ECN Spray A baseline condition is investigated in a dual-fuel (DF) configuration using methanol as a primary fuel. Finally, the cavitation modeling using the RFM model is investigated in two different configurations, including a transparent injector using water and an industrial injector using ammonia. It has been demonstrated that the model is able to dynamically predict the phase transition process under different operating conditions.La récente législation stricte sur les émissions pose de nouveaux défis à l'utilisation continue des moteurs à combustion interne à moteur diesel en raison de leurs émissions de dioxyde de carbone et de la pollution urbaine, qui accélèrent le changement climatique et sont liées à de graves problèmes de santé, respectivement. Les moteurs à combustion interne à double carburant (DFICE) utilisant des carburants renouvelables alternatifs font partie des concepts prometteurs pour réduire les émissions de polluants dans les applications où l'électrification n'est pas considérée comme une solution réalisable au problème des émissions, comme les cargos et les camions lourds. La conception efficace des équipements d'injection de carburant (FIE) est considérée comme une priorité essentielle pour le développement industriel des DFICE. Ainsi, des outils de conception et de simulation avancés sont nécessaires pour obtenir de meilleures conceptions de tels systèmes à double carburant. En conséquence, l'objectif principal de la thèse actuelle est de développer un modèle CFD prédictif et efficace pour les simulations d'écoulements diphasiques multi-composants dans le contexte de DFICE utilisant des carburants renouvelables tels que le méthanol ou l'ammoniac sous différentes conditions thermodynamiques (sous- et super-critiques), permettant une transition automatique/en douceur entre ces régimes qui peuvent coexister pendant les événements d'injection et de mélange de carburant. Plus précisément, les travaux en cours proposent un modèle de fluide réel (RFM) diphasique multi-composants entièrement compressible avec une interface diffusée et fermé par une méthode de tabulation d'équilibre thermodynamique basée sur diverses équations d'état de fluide réel (EoSs). L'approche de tabulation thermodynamique des fluides réels proposée peut en outre gérer les systèmes ternaires en plus des systèmes binaires. La table thermodynamique est générée à l'aide de la bibliothèque thermodynamique interne Carnot, qui effectue le calcul de l'équilibre vapeur-liquide (VLE) à l'aide d'un flash robuste isotherme-isobare (TPn) couplé à divers EoS à fluide réel. Le modèle proposé est d'abord appliqué pour étudier les processus de changement de phase et de mélange d'une seule gouttelette de n-dodécane dans un environnement bi-composant composé d'azote et de méthanol à haute pression, imitant une configuration bi-carburant à l'aide de simulations hautement résolues. Ensuite, pour traiter l'injection de carburant à haute pression, un modèle d'atomisation de fluide réel est proposé, dans lequel le modèle RFM est couplé à un modèle de sous-maille (SGS), utilisant une approche de densité de surface pour modéliser l'atomisation du carburant dans le cadre LES. L'injecteur Engine Combustion Network (ECN) Spray A est utilisé comme référence pour la validation du modèle proposé. Les résultats numériques obtenus ont montré un bon accord avec les différentes données expérimentales ECN. En outre, une variation paramétrique des conditions ECN Spray A a montré la capacité du modèle RFM à bien prédire les variations expérimentales des caractéristiques de spray. Suite à la validation du modèle, la condition de référence ECN Spray A est étudiée dans une configuration bi-carburant (DF) utilisant du méthanol comme carburant principal. Enfin, la modélisation de la cavitation à l'aide du modèle RFM est étudiée dans deux configurations différentes, dont un injecteur transparent utilisant de l'eau et un injecteur industriel utilisant de l'ammoniac. Il a été démontré que le modèle est capable de prédire dynamiquement le processus de transition de phase dans différentes conditions de fonctionnement

Modélisation de la rupture, du changement de phase et du mélange d'un jet de double carburant

La récente législation stricte sur les émissions pose de nouveaux défis à l'utilisation continue des moteurs à combustion interne à moteur diesel en raison de leurs émissions de dioxyde de carbone et de la pollution urbaine, qui accélèrent le changement climatique et sont liées à de graves problèmes de santé, respectivement. Les moteurs à combustion interne à double carburant (DFICE) utilisant des carburants renouvelables alternatifs font partie des concepts prometteurs pour réduire les émissions de polluants dans les applications où l'électrification n'est pas considérée comme une solution réalisable au problème des émissions, comme les cargos et les camions lourds. La conception efficace des équipements d'injection de carburant (FIE) est considérée comme une priorité essentielle pour le développement industriel des DFICE. Ainsi, des outils de conception et de simulation avancés sont nécessaires pour obtenir de meilleures conceptions de tels systèmes à double carburant. En conséquence, l'objectif principal de la thèse actuelle est de développer un modèle CFD prédictif et efficace pour les simulations d'écoulements diphasiques multi-composants dans le contexte de DFICE utilisant des carburants renouvelables tels que le méthanol ou l'ammoniac sous différentes conditions thermodynamiques (sous- et super-critiques), permettant une transition automatique/en douceur entre ces régimes qui peuvent coexister pendant les événements d'injection et de mélange de carburant. Plus précisément, les travaux en cours proposent un modèle de fluide réel (RFM) diphasique multi-composants entièrement compressible avec une interface diffusée et fermé par une méthode de tabulation d'équilibre thermodynamique basée sur diverses équations d'état de fluide réel (EoSs). L'approche de tabulation thermodynamique des fluides réels proposée peut en outre gérer les systèmes ternaires en plus des systèmes binaires. La table thermodynamique est générée à l'aide de la bibliothèque thermodynamique interne Carnot, qui effectue le calcul de l'équilibre vapeur-liquide (VLE) à l'aide d'un flash robuste isotherme-isobare (TPn) couplé à divers EoS à fluide réel. Le modèle proposé est d'abord appliqué pour étudier les processus de changement de phase et de mélange d'une seule gouttelette de n-dodécane dans un environnement bi-composant composé d'azote et de méthanol à haute pression, imitant une configuration bi-carburant à l'aide de simulations hautement résolues. Ensuite, pour traiter l'injection de carburant à haute pression, un modèle d'atomisation de fluide réel est proposé, dans lequel le modèle RFM est couplé à un modèle de sous-maille (SGS), utilisant une approche de densité de surface pour modéliser l'atomisation du carburant dans le cadre LES. L'injecteur Engine Combustion Network (ECN) Spray A est utilisé comme référence pour la validation du modèle proposé. Les résultats numériques obtenus ont montré un bon accord avec les différentes données expérimentales ECN. En outre, une variation paramétrique des conditions ECN Spray A a montré la capacité du modèle RFM à bien prédire les variations expérimentales des caractéristiques de spray. Suite à la validation du modèle, la condition de référence ECN Spray A est étudiée dans une configuration bi-carburant (DF) utilisant du méthanol comme carburant principal. Enfin, la modélisation de la cavitation à l'aide du modèle RFM est étudiée dans deux configurations différentes, dont un injecteur transparent utilisant de l'eau et un injecteur industriel utilisant de l'ammoniac. Il a été démontré que le modèle est capable de prédire dynamiquement le processus de transition de phase dans différentes conditions de fonctionnement.The recent stringent emissions legislation poses new challenges to the continued use of diesel-powered internal combustion engines due to their carbon dioxide emissions and urban pollution, which accelerate climate change and are linked to severe health problems, respectively. Dual-fuel internal combustion engines (DFICE) using alternative renewable fuels are among the promising concepts for reducing pollutant emissions in applications where electrification is not considered a feasible solution to the emissions problem, such as cargo ships and heavy-duty trucks. The effective design of the fuel injection equipment (FIE) is considered a key priority for the industrial development of the DFICEs. Thus, advanced design and simulation tools are required to achieve better designs of such dual-fuel systems. Accordingly, the main objective of the current thesis is to develop a predictive and efficient CFD model for multi-component two-phase flow simulations in the context of DFICE employing renewable fuels such as methanol or ammonia under different thermodynamic (sub- and super-critical) regimes, allowing an automatic/smooth transition between these regimes that can coexist during the fuel injection and mixing events. More specifically, the current work proposes a fully compressible multi-component two-phase real-fluid model (RFM) with a diffused interface and closed by a thermodynamic equilibrium tabulation method based on various real-fluid equations of state (EoSs). The proposed real-fluid thermodynamic tabulation approach can further handle ternary systems in addition to binary systems. The thermodynamic table is generated using the in-house Carnot thermodynamic library, which performs the vapor-liquid equilibrium (VLE) calculation using a robust isothermal-isobaric (TPn) flash coupled to various real-fluid EoSs. The proposed model is first applied to investigate the phase change and mixing processes of a single n-dodecane droplet in a bi-component environment composed of nitrogen and methanol at high pressure, mimicking a dual-fuel configuration using highly resolved simulations. Next, to address high-pressure fuel injection, a real fluid atomization model is proposed, in which the RFM model is coupled to a subgrid-scale (SGS) model, employing a surface density approach to model fuel atomization within the LES framework. The Engine Combustion Network (ECN) Spray A injector is used as a reference for the proposed model validation. The obtained numerical results have shown good agreement with the various ECN experimental data. Besides, a parametric variation of the ECN Spray A conditions has shown the capability of the RFM model to well predict the experimental variations of the spray characteristics. Following the model validation, the ECN Spray A baseline condition is investigated in a dual-fuel (DF) configuration using methanol as a primary fuel. Finally, the cavitation modeling using the RFM model is investigated in two different configurations, including a transparent injector using water and an industrial injector using ammonia. It has been demonstrated that the model is able to dynamically predict the phase transition process under different operating conditions

Modeling and LES of High-Pressure Liquid Injection Under Evaporating and Non-Evaporating Conditions by a Real Fluid Model and Surface Density Approach

International audienceNumerical modeling of high-pressure liquid fuel injection remains a challenge in various applications. Indeed, experimental observations have shown that injected liquid fuel jet undergoes a continuous change of state from classical two-phase atomization and spray droplets evaporation to a dense-fluid mixing phenomenon depending on the ambient pressure, temperature, and fuel properties. Accordingly, a predictive and efficient computational fluid dynamics (CFD) model that can represent the possible coexistence of subcritical and supercritical regimes during the fuel injection event is required. The widely used Lagrangian Discrete Droplet Method (DDM) requires parameter tuning of model constants and cannot model the dense near-nozzle region. Meanwhile, the high computational cost of Interface Capturing Methods (ICM) has prohibited their application to industrial cases. Thus, another alternative is an Eulerian Diffuse Interface Model (DIM), where the unresolved interface features are modeled instead of being tracked. Accordingly, the current work proposes a fully compressible multi-component two-phase real-fluid model (RFM) with a diffused interface and closed by a thermodynamic equilibrium tabulation method based on a real-fluid equation of state. The RFM model is complemented with a postulated surface density equation for fuel atomization modeling within the Large Eddy Simulation (LES) framework. The Engine Combustion Network (ECN) Spray A injector non-evaporating and nominal evaporating conditions are used as a reference for the proposed model validation. Simulations are performed using the proposed RFM model that has been implemented in the CONVERGE CFD solver. Under the non-evaporating condition, the RFM model can capture well the fuel mass distribution in the near-nozzle field, but also the interfacial surface area. Besides, the predicted drop size from simulations falls within the experimental data range. On the other hand, under the evaporating condition, spray liquid and vapor penetrations and fuel mixture fraction distribution are also accurately predicted. The vaporization effect on the surface area density is revealed to enhance surface generation in the dense spray region while reducing the surface density in the dilute spray region. The mean droplet size is also relatively reduced under the evaporating condition in the diluted spray region. Overall, the accuracy and computationally efficiency of the proposed RFM model coupled with the surface density equation for high-pressure fuel injection modeling are confirmed, allowing its use for high pressure industrial configurations in future studies

Numerical Investigation of Droplet Evaporation in High-Pressure Dual-Fuel Conditions Using a Tabulated Real-Fluid Model

International audienceThe substitution of diesel by cleaner renewable fuels such as short-chain alcohols in dual-fuel internal combustion engines is considered an attractive solution to reduce the pollutant emissions from internal combustion engines. In this context, two-phase flow models for multi-component mixtures considering the real-fluid thermodynamics are required for further understanding the evaporation and mixing processes in transcritical conditions. The present study proposes an efficient real-fluid model (RFM) based on a two-phase, fully compressible four-equation model under mechanical and thermal equilibrium assumptions with a diffused interface and closed by a thermodynamic equilibrium tabulation approach. Compared to previous research limited to binary mixtures tabulation, the proposed pre-tabulation approach can further handle ternary mixtures using a thermodynamic table that has been coupled to the CONVERGE CFD solver. The newly developed RFM model has been applied to investigate the evaporation of an n-dodecane droplet in a mixed ambient (methanol and nitrogen) relevant to dual-fuel configuration compared to pure nitrogen ambient. The four equation model is closed by a tabulated Cubic Plus Association (CPA) and Peng–Robinson (PR) equations of state for the droplet evaporation in a mixed and single component ambient, respectively. Numerical predictions show that the n-dodecane droplet lifetime decreases monotonically with increasing the methanol ambient concentration under the considered transcritical conditions. The performed thermodynamic analysis demonstrates that the droplet follows a different thermodynamic path as a function of the methanol ambient concentration. The different mechanisms contributing to the droplet lifetime behavior under varying ambient conditions are discussed

Exploring the Interaction between Phase Separation and Turbulent Fluid Dynamics in Multi-Species Supercritical Jets using a Tabulated Real-Fluid Model

International audienceToday, injection of liquid fuels at supercritical pressures is a frequently used technique to improve the efficiency of energy systems and address environmental constraints. This paper focuses on the analysis of the coupling between the hydrodynamics and thermodynamics of multi-species supercritical jets. Various phase transition phenomena, such as droplet formation process by condensation, which have been shown experimentally to significantly affect the flow and mixing dynamics of the jet, are studied. For this purpose, a tabulated multicomponent real fluid model assuming vapor-liquid equilibrium is proposed for the simulation of turbulent n-hexane jets injected with different inflow temperatures (480 K, 560 K, 600 K) into supercritical nitrogen at 5 MPa and 293 K. Numerical results are compared with available experimental data but also with published numerical studies, showing a good agreement. In addition, comparisons between different turbulence models, including the LES Sigma, Smagorinsky and RANS K − ϵ models have been performed, showing the relevance of the LES Sigma model for these very complex two-phase flows