Computational study of the cavitation phenomenon and its interaction with the turbulence developed in diesel injector nozzles by Large Eddy Simulation (LES)

Salvador, F.J.; Martinez-Lopez, J I; Romero, Javier; Roselló, M.-D.

doi:10.1016/j.mcm.2011.10.050

Cited by 60 publications

(37 citation statements)

References 14 publications

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“…Despite the transient flow and motion of the needle, it is common practice to simulate the flow as steady state at different fixed needle lifts [18] [19] [20] [21], or only at full needle lift [22]. Some work has been done on the effect of the needle's motion on the flow.…”

Section: Introduction Backgroundmentioning

confidence: 99%

Numerical Modelling of the In-Nozzle Flow of a Diesel Injector with Moving Needle during and after the End of a Full Injection Event

Papadopoulos¹,

Aleiferis²

2015

SAE Int. J. Engines

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The design of a Diesel injector is a key factor in achieving higher engine efficiency. The injector's fuel atomisation characteristics are also critical for minimising toxic emissions such as unburnt Hydrocarbons (HC). However, when developing injection systems, the small dimensions of the nozzle render optical experimental investigations very challenging under realistic engine conditions. Therefore, Computational Fluid Dynamics (CFD) can be used instead. For the present work, transient, Volume Of Fluid (VOF), multiphase simulations of the flow inside and immediately downstream of a real-size multi-hole nozzle were performed, during and after the injection event with a small air chamber coupled to the injector downstream of the nozzle exit. A Reynolds Averaged Navier-Stokes (RANS) approach was used to account for turbulence. Grid dependency studies were performed with 200k-1.5M cells. Both k- and k- SST models were considered in the validation process, with the k- SST found to predict better the injector's flow rate. The cavitation models of Schnerr-Sauer and the Zwart-GerberBelamri were employed for validation against optical data of cavitation in a simplified nozzle geometry obtained from the literature. The Schnerr-Sauer model was in better agreement with the experiments, hence this model was subsequently employed for the real injector simulations. The motion of the injector needle was modeled by a dynamic grid methodology. An injection pressure of 400 bar was applied at the inlet of the injector. Two outlet pressures were examined, 60 bar and 1 bar. The results showed that the flow was far from steady-state during the injection event and that hysteresis existed between the needle opening and closing phases. This indicated the importance of transient simulations, contrary to widely-used steady state simulations at fixed needle lifts. The two outlet pressures resulted in very different final states of the flowfield in the nozzle. Specifically, the nozzle ended up either full of liquid fuel at the end of injection or full of air after most of the fuel had been ejected into the chamber downstream. These predictions highlighted phenomena that can increase HC emissions due to fuel leakage, as well as processes that may be linked to different formation mechanisms of nozzle deposits.

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Section: Introduction Backgroundmentioning

confidence: 99%

Numerical Modelling of the In-Nozzle Flow of a Diesel Injector with Moving Needle during and after the End of a Full Injection Event

Papadopoulos¹,

Aleiferis²

2015

SAE Int. J. Engines

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“…[42] versions belongs to the homogeneous equilibrium models (HEM), and therefore assumes the flow as a perfect mixture of liquid and vapour phases in each cell of the domain. In HEM models it is assumed local kinematic equilibrium (local velocity is the same for both phases) and local thermodynamic equilibrium (temperature, pressure and free Gibbs enthalpy equality between phases).…”

Section: Introductionmentioning

confidence: 99%

Large-eddy simulation analysis of the influence of the needle lift on the cavitation in diesel injector nozzles

Desantes

Salvador

Carreres

et al. 2014

Proceedings of the Institution of Mechanical Engineers, Part D:

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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.

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“…For the LES modeling, a k-equation eddy-viscosity model [14], [15] was chosen using the Bussinesq function of the form (12) Where B is the turbulent energy generation term, (13) Of which the Smagorinsky model is a subset where the energy balance between the dissipation term from 12 equals the generation term 13. Salvador et al [16] used the Smagorinsky approach but others have rejected it for highly constrained problems.…”

Section: Methodsmentioning

confidence: 99%

“…Where B is the turbulent energy generation term, (13) Of which the Smagorinsky model is a subset where the energy balance between the dissipation term from 12 equals the generation term 13. Salvador et al [16] used the Smagorinsky approach but others have rejected it for highly constrained problems.It is generally accepted that the applicability of LES to planar simulation is limited since it is attempting to capture the 3D effects of vorticity and turbulent kinetic energy structures. Important turbulence mechanisms such as vortex stretching are not found in 2D flows.…”

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confidence: 99%

Near Nozzle Field Conditions in Diesel Fuel Injector Testing

Pearce

Hardalupas

Taylor

2015

SAE Technical Paper Series

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The measurement of the rate of fuel injection using a constant volume, fluid filled chamber and measuring the pressure change as a function of time due to the injected fluid (the so called "Zeuch" method) is an industry standard due to its simple theoretical underpinnings. Such a measurement device is useful to determine key timing and quantity parameters for injection system improvements to meet the evolving requirements of emissions, power and economy. This study aims to further the understanding of the nature of cavitation which could occur in the near nozzle region under these specific conditions of liquid into liquid injection using high pressure diesel injectors for heavy duty engines. The motivation for this work is to better understand the temporal signature of the pressure signals that arise in a typical injection cycle.A preliminary CFD study was performed, using OpenFOAM, with a transient (Large Eddy Simulation -LES), multiphase solver using the homogenous equilibrium model for the compressibility of the liquid/ vapour. The nozzle body was modelled for simplicity without the nozzle needle using a nozzle hole of 200μm diameter and the body pressurised to values typical for common rail engines. Temperature effects were neglected and the wall condition assumed to be adiabatic. The chamber initial static pressure was varied between 10 and 50 bar to reflect typical testing conditions.Results indicate that vapour formation could occur in areas 10-30mm distant from the nozzle itself. The cavitation was initiated around 100 μs after the jet had started for low ΔP cases and followed the development period required for the formation of vortices associated with the vortex roll up of this jet. These vortices had localised sites, in their core region, below the vapour pressure and were convected downstream of their initial formation location. It was also found that vapour formation could occur at chamber static pressures up to 50 bar (the highest tested) due to cavitation in the shear layer and this vortex effect. The pressure signal received at the chamber would therefore be more difficult to interpret with additional error components. IntroductionFuel injectors are under constant scrutiny as one of the prime factors in governing the overall efficiency and emissions output from heavy duty diesel engines. Manufacturers of fuel systems are therefore pursuing increasingly challenging targets for the accurate quantification of the instantaneous mass flow rate and total fuel quantity delivered. The characteristics of the fuel delivered such as the time rate of change of mass flow for a given pressure differential (i.e. rail pressure) are as important as the total quantity delivered for a given "shot". The rate of change of fuel mass flow is an important consideration to engine developers as it allows more complex combustion strategies that can be tailored for a given engine configuration and application [1,2]. This 'rate shaping' is a useful tool in order to gain the incremental improvements of combustion that...

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Computational study of the cavitation phenomenon and its interaction with the turbulence developed in diesel injector nozzles by Large Eddy Simulation (LES)

Cited by 60 publications

References 14 publications

Numerical Modelling of the In-Nozzle Flow of a Diesel Injector with Moving Needle during and after the End of a Full Injection Event

Numerical Modelling of the In-Nozzle Flow of a Diesel Injector with Moving Needle during and after the End of a Full Injection Event

Large-eddy simulation analysis of the influence of the needle lift on the cavitation in diesel injector nozzles

Near Nozzle Field Conditions in Diesel Fuel Injector Testing

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