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- Grosshans, H., et al.
(författare)
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Fuel jet mixing enhanced by intermittent injection
- 2013
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Ingår i: 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781624101816
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Konferensbidrag (refereegranskat)abstract
- The paper considers the effects of intermittent injection of a fuel spray on the initial break-up and mixing of the fuel with the surrounding "ambient" fluid. The two fluids may have the same phase or different phases. The aim of the analysis is to describe the physical process and indicate the mechanisms that control the mixing under different flow conditions (time-dependent injection and its frequency relative to the time scales of the flow) and fluid properties (Schmidt number in the single phase case or the Weber number for liquid fuel case. The computations use Large Eddy Simulation (LES) for accounting for turbulence and either Volume Of Fluid (VOF) for the initial break-up and Lagrangian Particle Tracking (LPT) with droplet break-up model in the case of liquid droplets injected into the ambient gas. The results show that depending on the physical properties of the fuel and ambient gas, the initial break-up and turbulent mixing can be enhanced substantially with intermittent injection. Most of the mixing is driven by the suction of ambient fluid at the tail of the injected fuel (as was shown experimentally and in a one dimensional model by Musculus and co-workers).
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| 3. |
- Grosshans, H., et al.
(författare)
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Mixing due pulsating turbulent jets
- 2014
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Ingår i: Springer Proceedings in Physics. - Cham : Springer. - 9783319018591 ; , s. 159-163
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Konferensbidrag (refereegranskat)abstract
- Combustion efficiency and the formation of soot and/or NOx in Internal- Combustion engines depends strongly on the local air/fuel mixture, the local flow conditions and temperature. Modern diesel engines employ high injection pressure for improved atomization, but mixing is controlled largely by the flow in the cylinder. By injecting the fuel in pulses one can gain control over the atomization, evaporation and the mixing of the gaseous fuel. We show that the pulsatile injection of fuel enhances fuel break-up and the entrainment of ambient air into the fuel stream. The entrainment level depends on fuel property, such as fuel/air viscosity and density ratio, fuel surface-tension, injection speed and injection sequencing. Examples of enhanced break-up and mixing are given.
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| 4. |
- Grosshans, H., et al.
(författare)
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Prediction and Measurement of the local extinction coefficient in sprays for 3D simulation/experiment data comparison
- 2015
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 72, s. 218-232
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Tidskriftsartikel (refereegranskat)abstract
- In the recent years, large progresses in laser imaging techniques have allowed to extract spatially resolved 2D and 3D quantitative spray information even in optically dense situations. The main breakthrough of these techniques is the possibility of suppressing unwanted effects from multiple light scattering using Structured Illumination. Thanks to this new feature, effects due to light extinction can also be corrected allowing the measurement of the local extinction coefficient. These quantitative information which is available even in challenging conditions, where Phase Doppler does not work anymore, can be used for data comparison between experiment and simulation. The local extinction coefficient is particularly valuable for the description of the droplet field, defined as the "spray region", as it contains information related to both droplets size and concentration. In this article we detail, then, the procedure enabling the modelers to obtain numerically this local extinction coefficient over the full 3D spray system. Following this procedure, results can now be adequately compared between simulation and experiment. The proposed comparison approach can better guide model adjustments in situation where the initial droplet size distribution is unknown or approximated and presents a step towards future validations of spray simulations, especially those based on Lagrangian Particle Tracking. The approach is exemplified here for the case of a Diesel-type spray. The results reveal at which specific spray locations discrepancies occur, and highlight the sensitivity of the initial droplet size distribution on the resulting extinction coefficient. (C) 2015 The Authors. Published by Elsevier Ltd.
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| 5. |
- Grosshans, H., et al.
(författare)
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Sensitivity of VOF simulations of the liquid jet breakup to physical and numerical parameters
- 2016
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Ingår i: Computers & Fluids. - : Elsevier. - 0045-7930 .- 1879-0747. ; 136, s. 312-323
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the characteristics of the primary breakup of a liquid jet is analyzed numerically. We applied the Volumes of Fluids (VOF) approach utilizing the Direction Averaged Curvature (DAC) model, to estimate the interface curvature, and the Direction Averaged Normal (DAN) model, to propagate the interface. While being used for the first time to predict liquid atomization, this methodology showed a high accuracy. The influence of varying the fluid properties, namely liquid-gas density and viscosity ratio, and injection conditions is discussed related to the required grid resolution. Resulting droplet sizes are compared to distributions obtained through the One-Dimensional Turbulence (ODT) model.
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