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Sibendu Som - One of the best experts on this subject based on the ideXlab platform.
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highly resolved eulerian simulations of fuel spray transients in single and multi hole injectors Nozzle Flow and near exit dynamics
Fuel, 2019Co-Authors: Michele Battistoni, Sibendu Som, Christopher F PowellAbstract:Abstract In high pressure fuel injectors, needle opening and closing transients cause complex off-design fluid dynamics behaviors that profoundly impact the spray and mixture formation processes. These dynamics are completely different from what is known to occur in steady state conditions. In this study, diesel spray transients have been investigated in single-hole and 3-hole Nozzles, encompassing internal and external Nozzle Flow and including needle motion, performing highly resolved (2.5 μm) computational fluid dynamics (CFD) simulations. We focused on end-of-injection (EOI) and start-of-injection (SOI) processes, in order to provide insights in to the physics. The liquid fuel, vapor and gas species are modeled with a single-fluid multiphase mixture approach, with diffuse interface, and with large eddy simulations (LES) of the turbulence. Occurrence of phase change due to cavitation is accounted for, and the spray dispersion is described with a turbulent dispersion model. Detailed needle motion data and orifice internal surface are available from x-ray synchrotron source measurements carried out at Argonne National Laboratory, and shared through the Engine Combustion Network (ECN) community. Simulations are compared against x-ray phase contrast imaging and radiography of the internal and near-exit Flow, in addition to optical microscopy data of the near-exit sprays. Simulation results are found to agree well with available experimental data, and are able to realistically capture local and global features. The simulations allow to gain insight into the physics of gas ingestion and dribbles at EOI, for different hole diameters, operating conditions and number of holes. At SOI, timing of liquid appearance out of the injector and spray tip penetration are adequately predicted, by using the EOI Flow field as in-Nozzle initialization, and by prescribing the measured tip needle displacement with an informed effective valve opening point inferred from the x-ray observations. Lastly, the variation of spreading angle over time is also discussed in detail for the multi-hole case, including hole-to-hole variations. Due to real geometry features and asymmetric needle motion with eccentric components, it is found that the three holes exhibit swirling Flows of increasing intensity as the lift decreases, causing the near cone angle to open and spread, in a quasi-hollow cone structure. These features are not observed in axial single-hole injectors because of their relative simplicity and intrinsic symmetry.
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modeling of flash boiling phenomenon in internal and near Nozzle Flow of fuel injectors
2018Co-Authors: Kaushik Saha, Michele Battistoni, Sibendu SomAbstract:Detailed analysis of the internal and the near-Nozzle Flow of fuel injectors is a necessity for a comprehensive understanding of any internal combustion engine performance. For gasoline direct injection engines, under part-load conditions, the in-cylinder pressure can be subatmospheric when the high-temperature fuel is injected, resulting in flash boiling. Detailed experimental characterization of such complex phenomena is extremely difficult. Three-dimensional computational fluid dynamics (CFD) simulations provide key insights into the flash boiling phenomena. The Spray G injector from Engine Combustion Network (ECN) has been considered for this study, which has eight counter-bored holes. Homogeneous relaxation model is used to capture the rate of phase change. Standard and RNG \(k-\epsilon \) turbulence models have been employed for modeling turbulence effects. Based on apriori thermodynamic estimates, three types of thermodynamic conditions have been explored: non-flashing, moderate flashing, and intense flashing. Numerical analyses showed that with more flashing the spray plumes grow wider due to the volume expansion of the rapidly forming fuel vapor. Mainly single-component fuel is studied in this work. Iso-octane is considered as the gasoline surrogate for this study. Binary component blends of isooctane and ethanol were also tested for blended fuel flashing predictions using the existing numerical setup. After careful estimation of blended fuel saturation properties, the simulations indicated that blended fuels can be more volatile than the individual components and thus exhibit more flashing compared to the cases with single-component fuels.
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Influence of fuel properties on internal Nozzle Flow development in a multi-hole diesel injector
Fuel, 2017Co-Authors: Roberto Torelli, Sibendu Som, Yuanjiang Pei, Yu Zhang, Michael TraverAbstract:Abstract Fuel physical properties are known to influence in-Nozzle Flow behavior, in turn affecting spray formation in internal combustion engines. A series of 3D simulations was performed to model the internal Nozzle Flow in a five-hole mini-sac diesel injector. The goal of the study was to evaluate the behavior of two gasoline-like fuels (full-range naphtha and light naphtha) and compare them against n-Dodecane, selected from a palette used as a diesel surrogate. Simulations were carried out using a multi-phase Flow representation based on the mixture model assumption with the Volume of Fluid (VOF) method, and including cavitation effects by means of the Homogeneous Relaxation Model (HRM). Validated methodologies from our previous studies were employed to account for full needle motion. Detailed simulations revealed the influence of the fuel properties on injector performance, injected fuel energy and propensity to cavitation. The three fuels were compared with respect to global parameters such as mass Flow rate and area contraction coefficients, and local parameters such as pressure and velocity distribution inside the sac and orifices. Parametric investigations were also performed to understand the fuel response to changes in the fuel injection temperature, injection pressure, and geometry details. Cavitation magnitude was observed to be strongly associated with the values of saturation pressure. Owing to their higher volatility, the two gasoline-like fuels were observed to cavitate more than n-Dodecane across all the investigated conditions. While at full needle lift cavitation was reduced for all fuels, during the injection transients the gasoline-like fuels showed more propensity to cavitate inside the orifice and seat regions. This is expected to have a profound influence on Nozzle erosion. Although full-range and light naphtha have lower densities compared to n-Dodecane, owing to their lower viscosity, the mass Flow rate differences between the naphtha fuels and n-Dodecane were small. The analysis of fuel energy content showed that the higher lower heating value (LHV) of light naphtha helped compensate for the slightly lower total delivered mass.
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in Nozzle Flow and spray characteristics for mineral diesel karanja and jatropha biodiesels
Applied Energy, 2015Co-Authors: Avinash Kumar Agarwal, Sibendu Som, Pravesh Chandra Shukla, Harsh Goyal, Douglas E LongmanAbstract:Abstract Superior spray behavior of fuels in internal combustion engines lead to improved combustion and emission characteristics therefore it is necessary to investigate fuel spray behavior of new alternative fuels. This study discusses the evolution of the in-Nozzle orifice parameters of a numerical simulation and the evolution of spray parameters of fuel spray in a constant-volume spray chamber during an experiment. This study compares mineral diesel, biodiesels (Karanja-and Jatropha-based), and their blends with mineral diesel. The results show that mineral diesel provides superior atomization and evaporation behavior compared to the biodiesel test fuels. Karanja biodiesel provides superior atomization and evaporation characteristics compared to Jatropha biodiesel. The qualitative comparison of simulation and experimental results in tandem shows that Nozzle-hole design is a critical parameter for obtaining optimum spray behavior in the engine combustion chamber.
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an eulerian cfd model and x ray radiography for coupled Nozzle Flow and spray in internal combustion engines
International Journal of Multiphase Flow, 2015Co-Authors: Qingluan Xue, Michele Battistoni, Christopher F Powell, Douglas E Longman, Shaoping Quan, Eric Pomraning, P K Senecal, David P Schmidt, Sibendu SomAbstract:Abstract This paper implements a coupled approach to integrate the internal Nozzle Flow and the ensuing fuel spray using a Volume-of-Fluid (VOF) method in the finite-volume framework. A VOF method is used to model the internal Nozzle two-phase Flow with a cavitation description closed by the homogeneous relaxation model of Bilicki and Kestin (1990). An Eulerian single velocity field approach by Vallet et al. (2001) is implemented for near-Nozzle spray modeling. This Eulerian approach considers the liquid and gas phases as a complex mixture with a highly variable density to describe near Nozzle dense sprays. The liquid mass fraction is transported with a model for the turbulent liquid diffusion flux into the gas. Fully-coupled Nozzle Flow and spray simulations are performed in three dimensions and validated against the X-ray radiography measurements of Kastengren et al. (2014) for a diesel fuel surrogate. A standard k – ∊ Reynolds Averaged Navier Stokes based turbulence model is used in this study and the influence of model constants is evaluated. First, the grid convergence study is performed. The effect of grid size is also evaluated by comparing the fuel distribution against experimental data. Finally, the fuel distribution predicted by the coupled Eulerian approach is compared against that by Lagrangian–Eulerian spray model along with experimental data. The coupled Eulerian approach provides a unique way of coupling the Nozzle Flow and sprays so that the effects of in-Nozzle Flow can be directly realized on the fuel spray. Both experiment and numerical simulations show non-cavitation occurring for this injector with convergent Nozzle geometry. The study shows that the Eulerian approach has advantages over near-field dense spray distributions.
N A Adams - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of cavitating Nozzle Flow and primary jet break up
Physics of Fluids, 2015Co-Authors: F Orley, Theresa Trummler, Stefan Hickel, S J Schmidt, N A AdamsAbstract:We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular Nozzle, which resembles a high aspect-ratio slot Flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating fluid model is based on a thermodynamic-equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The thermodynamic model is embedded into an implicit large-eddy simulation (LES) environment. The considered configuration follows the general setup of a reference experiment and is a generic reproduction of a scaled-up fuel injector or control valve as found in an automotive engine. Due to the experimental conditions, it operates, however, at significantly lower pressures. LES results are compared to the experimental reference for validation. Three different operating points are studied, which differ in terms of the development of cavitation regions and the jet break-up characteristics. Observed differences between experimental and numerical data in some of the investigated cases can be caused by uncertainties in meeting nominal parameters by the experiment. The investigation reveals that three main mechanisms promote primary jet break-up: collapse-induced turbulent fluctuations near the outlet, entrainment of free gas into the Nozzle, and collapse events inside the jet near the liquid-gas interface.
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large eddy simulation of cavitating Nozzle Flow and primary jet break up
Physics of Fluids, 2015Co-Authors: F Orley, Theresa Trummler, Stefan Hickel, S J Schmidt, N A AdamsAbstract:We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular Nozzle, which resembles a high aspect-ratio slot Flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating fluid model is based on a thermodynamic-equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The thermodynamic model is embedded into an implicit large-eddy simulation (LES) environment. The considered configuration follows the general setup of a reference experiment and is a generic reproduction of a scaled-up fuel injector or control valve as found in an automotive engine. Due to the experimental conditions, it operates, however, at significantly lower pressures. LES results are compared to the experimental reference for validation. Three different operating points are studied, which differ in terms of the development of cavitation regions and the jet break-up characteristics. Observed differences between experimental and numerical data in some of the investigated cases can be caused by uncertainties in meeting nominal parameters by the experiment. The investigation reveals that three main mechanisms promote primary jet break-up: collapse-induced turbulent fluctuations near the outlet, entrainment of free gas into the Nozzle, and collapse events inside the jet near the liquid-gas interface.
Stefan Hickel - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of cavitating Nozzle Flow and primary jet break up
Physics of Fluids, 2015Co-Authors: F Orley, Theresa Trummler, Stefan Hickel, S J Schmidt, N A AdamsAbstract:We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular Nozzle, which resembles a high aspect-ratio slot Flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating fluid model is based on a thermodynamic-equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The thermodynamic model is embedded into an implicit large-eddy simulation (LES) environment. The considered configuration follows the general setup of a reference experiment and is a generic reproduction of a scaled-up fuel injector or control valve as found in an automotive engine. Due to the experimental conditions, it operates, however, at significantly lower pressures. LES results are compared to the experimental reference for validation. Three different operating points are studied, which differ in terms of the development of cavitation regions and the jet break-up characteristics. Observed differences between experimental and numerical data in some of the investigated cases can be caused by uncertainties in meeting nominal parameters by the experiment. The investigation reveals that three main mechanisms promote primary jet break-up: collapse-induced turbulent fluctuations near the outlet, entrainment of free gas into the Nozzle, and collapse events inside the jet near the liquid-gas interface.
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large eddy simulation of cavitating Nozzle Flow and primary jet break up
Physics of Fluids, 2015Co-Authors: F Orley, Theresa Trummler, Stefan Hickel, S J Schmidt, N A AdamsAbstract:We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular Nozzle, which resembles a high aspect-ratio slot Flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating fluid model is based on a thermodynamic-equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The thermodynamic model is embedded into an implicit large-eddy simulation (LES) environment. The considered configuration follows the general setup of a reference experiment and is a generic reproduction of a scaled-up fuel injector or control valve as found in an automotive engine. Due to the experimental conditions, it operates, however, at significantly lower pressures. LES results are compared to the experimental reference for validation. Three different operating points are studied, which differ in terms of the development of cavitation regions and the jet break-up characteristics. Observed differences between experimental and numerical data in some of the investigated cases can be caused by uncertainties in meeting nominal parameters by the experiment. The investigation reveals that three main mechanisms promote primary jet break-up: collapse-induced turbulent fluctuations near the outlet, entrainment of free gas into the Nozzle, and collapse events inside the jet near the liquid-gas interface.
Douglas E Longman - One of the best experts on this subject based on the ideXlab platform.
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in Nozzle Flow and spray characteristics for mineral diesel karanja and jatropha biodiesels
Applied Energy, 2015Co-Authors: Avinash Kumar Agarwal, Sibendu Som, Pravesh Chandra Shukla, Harsh Goyal, Douglas E LongmanAbstract:Abstract Superior spray behavior of fuels in internal combustion engines lead to improved combustion and emission characteristics therefore it is necessary to investigate fuel spray behavior of new alternative fuels. This study discusses the evolution of the in-Nozzle orifice parameters of a numerical simulation and the evolution of spray parameters of fuel spray in a constant-volume spray chamber during an experiment. This study compares mineral diesel, biodiesels (Karanja-and Jatropha-based), and their blends with mineral diesel. The results show that mineral diesel provides superior atomization and evaporation behavior compared to the biodiesel test fuels. Karanja biodiesel provides superior atomization and evaporation characteristics compared to Jatropha biodiesel. The qualitative comparison of simulation and experimental results in tandem shows that Nozzle-hole design is a critical parameter for obtaining optimum spray behavior in the engine combustion chamber.
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an eulerian cfd model and x ray radiography for coupled Nozzle Flow and spray in internal combustion engines
International Journal of Multiphase Flow, 2015Co-Authors: Qingluan Xue, Michele Battistoni, Christopher F Powell, Douglas E Longman, Shaoping Quan, Eric Pomraning, P K Senecal, David P Schmidt, Sibendu SomAbstract:Abstract This paper implements a coupled approach to integrate the internal Nozzle Flow and the ensuing fuel spray using a Volume-of-Fluid (VOF) method in the finite-volume framework. A VOF method is used to model the internal Nozzle two-phase Flow with a cavitation description closed by the homogeneous relaxation model of Bilicki and Kestin (1990). An Eulerian single velocity field approach by Vallet et al. (2001) is implemented for near-Nozzle spray modeling. This Eulerian approach considers the liquid and gas phases as a complex mixture with a highly variable density to describe near Nozzle dense sprays. The liquid mass fraction is transported with a model for the turbulent liquid diffusion flux into the gas. Fully-coupled Nozzle Flow and spray simulations are performed in three dimensions and validated against the X-ray radiography measurements of Kastengren et al. (2014) for a diesel fuel surrogate. A standard k – ∊ Reynolds Averaged Navier Stokes based turbulence model is used in this study and the influence of model constants is evaluated. First, the grid convergence study is performed. The effect of grid size is also evaluated by comparing the fuel distribution against experimental data. Finally, the fuel distribution predicted by the coupled Eulerian approach is compared against that by Lagrangian–Eulerian spray model along with experimental data. The coupled Eulerian approach provides a unique way of coupling the Nozzle Flow and sprays so that the effects of in-Nozzle Flow can be directly realized on the fuel spray. Both experiment and numerical simulations show non-cavitation occurring for this injector with convergent Nozzle geometry. The study shows that the Eulerian approach has advantages over near-field dense spray distributions.
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a comparison of injector Flow and spray characteristics of biodiesel with petrodiesel
Fuel, 2010Co-Authors: Sibendu Som, Douglas E Longman, Anita I Ramirez, Suresh K AggarwalAbstract:Abstract Performance and emission characteristics of compression ignition engines depend strongly on inner Nozzle Flow and spray behavior. These processes control the fuel air mixing, which in turn is critical for the combustion process. The differences in the physical properties of petrodiesel and biodiesel are expected to significantly alter the inner Nozzle Flow and spray structure and, thus, the performance and emission characteristics of the engine. In this study, the inner Nozzle Flow dynamics of these fuels are characterized by using the mixture-based cavitation model in FLUENT v6.3. Because of its lower vapor pressure, biodiesel was observed to cavitate less than petrodiesel. Higher viscosity of biodiesel resulted in loss of Flow efficiency and reduction in injection velocity. Turbulence levels at the Nozzle orifice exit were also lower for biodiesel. Using the recently developed KH-ACT model, which incorporates the effects of cavitation and turbulence in addition to aerodynamic breakup, the inner Nozzle Flow simulations are coupled with the spray simulations in a “quasi-dynamic” fashion. Thus, the influence of inner Nozzle Flow differences on spray development of these fuels could be captured, in addition to the effects of their physical properties. Spray penetration was marginally higher for biodiesel, while cone angle was lower, which was attributed to its poor atomization characteristics. The computed liquid lengths of petrodiesel and biodiesel were compared with data from Sandia National Laboratories. Liquid lengths were higher for biodiesel due to its higher boiling temperature and heat of vaporization. Though the simulations captured this trend well, the liquid lengths were underpredicted, which was attributed to uncertainty about the properties of biodiesel used in the experiments. Parametric studies were performed to determine a single parameter that could be used to account for the observed differences in the fuel injection and spray behavior of petrodiesel and biodiesel; fuel temperature seems to be the best parameter to tune.
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investigation of Nozzle Flow and cavitation characteristics in a diesel injector
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2010Co-Authors: Sibendu Som, Suresh K Aggarwal, Essam Elhannouny, Douglas E LongmanAbstract:Cavitation and turbulence inside a diesel injector play a critical role in primary spray breakup and development processes. The study of cavitation in realistic injectors is challenging, both theoretically and experimentally, since the associated two-phase Flow field is turbulent and highly complex, characterized by large pressure gradients and small orifice geometries. We report herein a computational investigation of the internal Nozzle Flow and cavitation characteristics in a diesel injector. A mixture based model in FLUENT V6.2 software is employed for simulations. In addition, a new criterion for cavitation inception based on the total stress is implemented, and its effectiveness in predicting cavitation is evaluated. Results indicate that under realistic diesel engine conditions, cavitation patterns inside the orifice are influenced by the new cavitation criterion. Simulations are validated using the available two-phase Nozzle Flow data and the rate of injection measurements at various injection pressures (800-1600 bar) from the present study. The computational model is then used to characterize the effects of important injector parameters on the internal Nozzle Flow and cavitation behavior, as well as on Flow properties at the Nozzle exit. The parameters include injection pressure, needle lift position, and fuel type. The propensity of cavitation for different on-fleetmore » diesel fuels is compared with that for n-dodecane, a diesel fuel surrogate. Results indicate that the cavitation characteristics of n-dodecane are significantly different from those of the other three fuels investigated. The effect of needle movement on cavitation is investigated by performing simulations at different needle lift positions. Cavitation patterns are seen to shift dramatically as the needle lift position is changed during an injection event. The region of significant cavitation shifts from top of the orifice to bottom of the orifice as the needle position is changed from fully open (0.275 mm) to nearly closed (0.1 mm), and this behavior can be attributed to the effect of needle position on Flow patterns upstream of the orifice. The results demonstrate the capability of the cavitation model to predict cavitating Nozzle Flows in realistic diesel injectors and provide boundary conditions, in terms of vapor fraction, velocity, and turbulence parameters at the Nozzle exit, which can be coupled with the primary breakup simulation.« less
J Martinezlopez - One of the best experts on this subject based on the ideXlab platform.
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comparison of microsac and vco diesel injector Nozzles in terms of internal Nozzle Flow characteristics
Energy Conversion and Management, 2015Co-Authors: F J Salvado, D Jaramillo, M Carreres, J MartinezlopezAbstract:Abstract A computational study focused on the inner Nozzle Flow and cavitation phenomena has been reported in this paper in order to investigate the two most common types of diesel injector Nozzles at the present: microsac and valve covered orifice (VCO). The geometrical differences among both types of Nozzles are mainly located at the needle seat, upstream of the discharge orifices. In the case of microsac Nozzles there is a small volume upstream of the discharge orifices which is not present in VCO Nozzles. Due to these geometrical differences among both type of Nozzles, differences in the inner Flow and the cavitation development have been found and analysed in this research. For the study, two cylindrical Nozzles with six orifices and the same outlet diameter have been experimentally characterized in terms of mass Flow rate. These measurements have been used to validate the CFD results obtained with the code OpenFOAM used for the analysis of the internal Nozzle Flow. For the simulations, two meshes that reproduce the microsac and VCO Nozzles seat geometry while keeping the same geometry at the orifices have been built. The simulations have been carried out with a code previously validated and able to simulate cavitation phenomena using a homogeneous equilibrium model (HEM) and with RANS approach for the turbulence modelling (RNG k – e ). For the computational study, three injection pressures and different geometries simulating different needle lifts have been used. The comparison among Nozzles has been made in terms of mass Flow, momentum flux and effective velocity and in terms of other non-dimensional parameters which are useful for describing the inner Nozzle Flow: discharge coefficient ( C d ), area coefficient ( C a ) and velocity coefficient ( C v ). The analysis performed by studying and comparing the particularities of the Flow in each Nozzle has been useful in order to explain the experimental differences found in terms of mass Flow rate and critical cavitation conditions. One of the main conclusions of this study is the higher influence of the needle on the mass Flow, momentum and injection velocity results for the VCO Nozzle as compared to the microsac one. Hence, whereas in the first one these variables scale with the needle lift value, in the second one there is an intermediate needle lift from which they stop being influenced by the presence of the needle. Furthermore, the study has also revealed important differences in the proneness to produce cavitation and its morphology. For the VCO Nozzle, cavitation phenomenon occurs only in the upper part of the orifice inlet. However, for the microsac Nozzle cavitation appears both at the upper and the lower part of the Nozzle orifice entrance.
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study of the influence of the needle lift on the internal Flow and cavitation phenomenon in diesel injector Nozzles by cfd using rans methods
Energy Conversion and Management, 2013Co-Authors: F J Salvador, J Martinezlopez, Miguel Caballer, C De AlfonsoAbstract:Abstract It 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 Nozzle modeling 10 different fixed needle lifts. The internal Flow has been modeled with a continuum Nozzle Flow model that considers the cavitating Flow as a homogeneous mixture of liquid and vapour. Due to high Reynolds numbers, turbulence effects have been taken into account by RANS methods using a RNG k – e model. Firstly, the code has been validated against experimental data at full needle lift conditions in terms of mass Flow, momentum flux and effective velocity, showing a fairly good agreement with experimental results. 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.
