Large-Eddy Simulation of turbulent, cavitating fuel flow inside a 9-hole Diesel injector including needle movement

Örley, Felix; Hickel, Stefan; Schmidt, Steffen J.; Adams, Nikolaus A.

doi:10.1177/1468087416643901

Cited by 48 publications

(44 citation statements)

References 60 publications

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“…Similar conclusions about the effect of the fuel properties have already been seen both experimentally and numerically for other kinds of biodiesel [27]- [31] and for winter fuel formulations [32]- [34]. Recently, a few authors [35]- [39] have showed that it is important to consider not only the changes in the fuel properties related to the fuel composition, but also those related to the different temperature and pressure conditions along the nozzle geometry, which are traditionally neglected.…”

supporting

confidence: 72%

Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures

Salvador

Morena

Martinez-Lopez

et al. 2017

Energy Conversion and Management

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Diesel fuel injection systems are being used at higher injection pressure conditions over time because of more stringent emissions requirements. Thus, the importance to properly take into account the fluid compressibility on injection CFD simulations is also increasing. In this paper, an investigation of the compressibility effects in nozzle flow simulations has been carried out for injection pressures up to 250 MPa. To do so, the fluid properties (including density, viscosity and speed of sound) have been measured in a wide range of boundary conditions. These measurements have allowed to obtain correlations for the fluid properties as a function of pressure and temperature. Then, these equations have been incorporated to a CFD solver to take into account the variation of the fluid properties with the pressure changes along the computational domain. The results from

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supporting

confidence: 72%

Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures

Salvador

Morena

Martinez-Lopez

et al. 2017

Energy Conversion and Management

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“…The needle lift profile was however approximated as linear in both the start and end of injection. In [4] a density-based solver with a cavitation model based on thermodynamic equilibrium and LES assumptions was applied to the main injection of a 9-hole injector with a realistic needle-lift profile. Two different designs of an injector showing erosive cavitation were instead simulated in [5].…”

Section: Introductionmentioning

confidence: 99%

Large Eddy Simulation of the Internal Injector Flow During Pilot Injection

Cristofaro¹,

Edelbauer²,

Koukouvinis³

et al. 2018

Proceedings of the 10th International Symposium on Cavitation (CAV2018)

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The aim of this work is to simulate the internal flow of a Diesel injector during an entire pilot injection event. In common rail systems a small quantity of fuel can be injected before the main injection is started. This increases the temperature in the combustion chamber and improves the combustion, leading to higher engine efficiency and reduced emissions. The internal nozzle flow during this short event is highly dynamic and vapor cavities may appear at the end of the injection. In order to study the flow characteristics, a numerical methodology based on the Eulerian multi-fluid approach is adopted. The filtered Navier-Stokes equations are discretized with the finite volume method and then solved with an implicit pressure-based solver. The flow field is modelled considering single pressure and velocity fields. The Coherent Structure Model is used to derive the eddy viscosity applied to the Large Eddy Simulation approach. The liquid evaporation rate is evaluated with a cavitation model based on the Rayleigh-Plesset equation for a single bubble. Even though thermodynamic equilibrium is not satisfied a priori, the main parameter is adjusted in order to limit the thermodynamic states to be in a range close to the equilibrium conditions. The liquid compressibility is modelled with a linear correlation between pressure and density variations. The needle longitudinal movement obtained from the experiments is applied to the simulation. The adopted geometry is the Spray A case defined by the Engine Combustion Network. It is an asymmetric single hole Diesel injector that has been extensively studied in the past both experimentally and numerically. The injection pressure is 1,500 [bar] and the ambient pressure is 60 [bar] with a fuel temperature of 363 K inside the injector. Pure n-dodecane is used as fluid in order to have a precise specification of the physical properties. Although both experiments and simulations showed no cavitation for completely open needle at fixed position, recent studies demonstrated that phase-change of the liquid can appear during the needle closing phase. Cavitation erosion prone locations are then evaluated by recording the maximum intensity of pressure on the surface.

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“…Results are presented for a micro-channel flow, as well as for a real injector case. Another cavitating injector simulation was presented by Örley et al in [12], where a density-based solver with explicit time integration and the single-fluid approach were applied. Pressure peak intensities in the order of 1000 [bar] were recorded in both works.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of compressible cavitating two-phase flows with a pressure-based solver

Cristofaro

Edelbauer

Gavaises

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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This work intends to study the effect of compressibility on throttle flow simulations with a pressure-based solver. The simple micro throttle geometry allows easier access for obtaining experimental data compared to a real injector, but still maintaining the main flow features. For this reasons it represents a meaningful and well reported benchmark for validation of numerical methods developed for cavitating injector flows. An implicit pressure-based compressible solver is used on the filtered Navier-Stokes equations. Thus, no stability limitation is applied on the time step. A common pressure field is computed for all phases, but different velocity fields are solved for each phase, following the multi-fluid approach. The liquid evaporation rate is evaluated with a Rayleigh-Plesset equation based cavitation model and the Coherent Structure Model is adopted as closure for the sub-grid scales in the momentum equation. The aim of this study is to show the capabilities of the pressure-based solver to deal with both vapor and liquid phases considered compressible. A comparison between experimental results and compressible simulations is presented. Time-averaged vapor distribution and velocity profiles are reported and discussed. The distribution of pressure maxima on the surface and the results from a semi-empirical erosion model are in good agreement with the erosion locations observed in the experiments. This test case aims to represent a benchmark for further application of the methodology to industrial relevant cases. Keywords cavitation erosion, compressible pressure-based, multi-fluid LES IntroductionDiesel injectors can suffer from cavitation erosion. Recent regulations in term of emissions forced engine manufacturers to increase the injection pressure to values above 2000 [bar]. The consequent higher velocities in the nozzle lead to the formation of a more diffused spray and, thus, better combustion. This causes higher engine efficiency and less emissions, but, at the same time, higher risk of cavitation. If the pressure reaches locally values below saturation pressure due to the high velocity, the liquid evaporates. Under certain conditions, the repetitive collapse of the generated vapor that is convected further downstream, where pressure is above the saturation pressure, may be an aggressive phenomenon. Fatigue damages can then appear on the nearby surfaces. Many works have been published in the last decades to predict cavitation erosion. Experimental campaigns are of crucial importance to gain a better understanding of the physical phenomena involved and to provide usable data for the validation of new models. Numerical approaches based on multi-phase Computational Fluid Dynamics (CFD) are able to model cavitating flow fields. Useful information can then be obtained to assess the probability of cavitation erosion appearance. A wide range of flow aggressiveness and erosion risk indices were developed in the recent years. A review of some selected cavitation erosion models, together with a descripti...

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Large-Eddy Simulation of turbulent, cavitating fuel flow inside a 9-hole Diesel injector including needle movement

Cited by 48 publications

References 60 publications

Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures

Assessment of compressibility effects on internal nozzle flow in diesel injectors at very high injection pressures

Large Eddy Simulation of the Internal Injector Flow During Pilot Injection

Numerical simulation of compressible cavitating two-phase flows with a pressure-based solver

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