ElsevierPayri González, F.; Payri, R.; Salvador Rubio, FJ.; Martínez López, J. (2012). A contribution to the understanding of cavitation effects in Diesel injector nozzles through a combined experimental and computational investigation. Computers and Fluids. 58:88-101. doi:10.1016/j.compfluid.2012 ABSTRACTIn this paper a combined experimental and computational study was carried out in order to assess the ability of a Homogeneous Equilibrium Model in predicting the experimental behaviour observed from the hydraulical characterization of a nozzle. The nozzle used was a six-orifice microsac nozzle, with cylindrical holes, and therefore inclined to cavitate. The experimental results available for the validation purpose comprised measurements of mass flow rate and spray momentum flux, which correctly combined provide also fundamental information such as discharge coefficient, nozzle exit effective velocity and area contraction. The model was proved to be able of 2 reproducing the experimental results with high degree of confidence and, through the exploration of the internal flow, allowed the explanation of widely reported experimental findings related to cavitation phenomena: the mass flow choking induced by cavitation and the increment of effective injection velocity.

Elsevier Salvador, FJ.; Martínez López, J.; Caballer Fernández, M.; Alfonso Laguna, CD. (2013). Study of the influence of the needle lift on the internal flow and cavitationphenomenon in diesel injector nozzles by CFD using RANS methods. Energy Conversion and Management. 66:246-256. doi:10.1016/j.enconman.2012.10 ABSTRACTIt is well known that cavitation phenomenon in diesel injector nozzles has a strong influence on the internal flow during the injection process and spray development.However, its influence on the flow during needle opening and closing remains still unclear due to the huge difficulties related to performing experiments at partial needle lifts.In this paper, an extended computational study has been performed in a multi-hole Once the code has been validated, it has been possible to study in depth the internal nozzle flow and its characteristics at the outlet at different partial needle lifts.Nevertheless, not only the main flow features have been explained, but also the cavitation appearance and the turbulence development, which present huge differences between the different needle lifts simulated.

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A combined experimental and computational investigation has been performed in order to evaluate the influence of physical properties of biodiesel on the injection process in a common-direct injection system with second generation solenoid injectors. For that purpose, after a complete characterization of the system, which involved mechanical and hydraulic characterization, a one-dimensional model has been obtained and extensively validated. Simulations have then been performed with a standard Diesel and a 100% rape methyl ester (RME) biodiesel which allowed a comparison and analysis of the dynamic response of the injector to be done. Different injection strategies involving main injection and main plus post-injection have been used to explore the impact of the use of biodiesel on the performance and stability of solenoid injectors.As far as the dynamic response of the injector is concerned, the results obtained have clearly shown that the use of biodiesel affects the dynamic response of the needle, especially at low injection pressures. The behavior of the system under multi-injection strategies (main plus post injection) has been also evaluated determining for different operating conditions (injection pressures and backpressures) the minimum dwell time between injections to assure a stable behavior in the injection process (mass flow rate).Important differences have been found between biodiesel and standard diesel in this critical parameter at low injection pressures, becoming less important at high injection pressure. Finally, a modification on the injector hardware has been proposed in order to compensate these differences.

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In this paper, the ability of a computational fluid dynamics code to reproduce cavitation phenomena accurately is checked by comparing data acquired by numerical simulations against those obtained from different experiments involving the mass flow, the momentum flux, and the effective injection velocity. Cavitation is modelled using a single-phase cavitation model based on a barotropic equation of state together with a homogeneous equilibrium assumption. In the research reported in this paper, the ability to use the code for actual diesel injector nozzle geometries and conditions has been checked and validated. The main contribution of the present investigation and what makes it different from previous work in the literature is the consideration of extended experimental data for validation purposes: the mass flow, the momentum flux at the nozzle exit, and the effective injection velocity. These are unique features in contrast with other publications, which normally take into account at the most, if at all, the cavitation morphology or the mass flow. The results obtained and their comparison with available experimental data show how the model is able to predict the behaviour of the fluid in such conditions with a high level of confidence.

COMPARISON OF MICROSAC AND VCO DIESEL INJECTOR NOZZLES IN TERMS ABSTRACT 23A computational study focused on the inner nozzle flow and cavitation phenomena has been 24 reported in this paper in order to investigate the two most common types of diesel injector nozzles 25 at the present: microsac and valve covered orifice (VCO). The geometrical differences among both 26 types of nozzles are mainly located at the needle seat, upstream of the discharge orifices. In the 27 case of microsac nozzles there is a small volume upstream of the discharge orifices which is not 28 present in VCO nozzles. Due to these geometrical differences among both type of nozzles, 45One of the main conclusions of this study is the higher influence of the needle on the mass flow, 46 momentum and injection velocity results for the VCO nozzle as compared to the microsac one.

Cavitation phenomenon has a strong influence on the internal flow and spray development in diesel injector nozzles. Despite its importance, there are lots of aspects which remain still unclear, especially at partial needle lifts when the injector is in the opening and closing phases. For that reason, the current paper is focused on the influence of the needle lift on the internal flow in a diesel nozzle. This study has been carried out with 3D simulations at high injection pressure (160 MPa) using a homogeneous equilibrium model implemented in OpenFOAM to model cavitation phenomenon.The nozzle has been simulated with LES methods at six different needle lifts (10, 30, 50, 75, 100 and 250 μm), providing relevant information about the evolution of the internal flow, the turbulence development (vorticity, turbulence-cavitation interaction and turbulent structures) and the flow characteristics in the nozzle outlet (mass flow, momentum flux and effective velocity) with the needle position.