bluuebunny/crossref_metadata_2025 huggingface dataset:
An improved image processing method for particle characterization by shadowgraphy
Authors: Wang Hua , Felis Francisco , Tomas Severine , Anselmet Fabien , Amielh Muriel
Published: September 2017

Shadowgraphy is one of the most popular imaging techniques to characterize moving particles by their size,geometry as well as velocity, due to its simplicity. However, it requires advanced image processing to handle various image defects such as non-uniform illumination, overlapped particles, etc., which are normally only solved for individual applications. This study proposes a robust image processing method for particle shadowgraphy, aiming to process imperfect particle shadow images. The proposed method first detects qualified particles from particle shadow images, and then processes detected particles individually. Therefore different defects from different particles can be handled separately and locally. An overlapped particles detection and separation algorithm is also implemented to improve the accuracy of size and geometry characterization.The proposed method is first proved by synthetic generated particle shadow images, followed by a proof test with shadow images from a transparent dot pattern target. Finally this method is successfully applied to a shadowimage acquired from a water spray and proved to be able to handle various issues of shadowgraphy.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4614
Numerical Simulation of the Dispersion and Deposition of a Spray Carried by a Pulsating Airflow in a Patient-Specific Human Nasal Cavity
Authors: Farnoud Ali , Cui Xinguang , Baumann Ingo , Gutheil Eva
Published: September 2017

The present numerical study concerns the dispersion and deposition of a nasal spray in a patient-specific human nose. The realistic three-dimensional geometry of the nasal cavity is reconstructed from computer tomography (CT) scans. Identification of the region of interest, removal of artifacts, segmentation, generation of the .STL file and the triangulated surface grid are performed using the software packages ImageJ, meshLab, and NeuRA2. An unstructured computational volume grid with approximately 15 million tetrahedral grid cells is generated using the software Ansys ICEM-CFD 11.0. An unsteady Eulerian-Lagrangian formulation is used to describe the airflow and the spray dispersion and deposition in the realistic human nasal airway using two-way coupling. A new solver called pimpleParcelFoam is developed, which combines the lagrangianParcel libraries with the pimpleFoam solver within the software package OpenFOAM 3.0.0. A large eddy simulation (LES) with the dynamic sub-grid scale (SGS) model is performed to study the spray in both a steady and a pulsating airflow with an inflow rate of 7.5 L/min (or maximum value in case of the pulsating spray) and a frequency of 45 Hz for pulsation as used in commercial inhalation devices. 10,000 mono-disperse particles with the diameters of 2.4 µm and 10 µm are uniformly injected at the nostrils. In order to fulfil the stability conditions for the numerical solution, a constant time-step of 10−5 s is implemented. The simulations are performed for a real process time of 1 s, since after the first second of the process, all particles have escaped through the pharynx or they are deposited at the surface of the nasal cavity. The numerical computations are performed on the high-performance computer bwForCluster MLS&WISO Production using 256 processors, which take around 32 and 75 hours for steady and pulsating flow simulation, respectively. The study shows that the airflow velocity reaches its maximum values in the nasal valve, in parts of the septum and in the nasopharynx. A complex airflow is observed in the vestibule and in the nasopharynx region, which may directly affect the dispersion and deposition pattern of the spray. The results reveal that the spray tends to deposit in the nasal valve, the septum and in the nasopharynx due to the change in the direction of the airflow in these regions. Moreover, it is found that due to the pulsating airflow, the aerosols are more dispersed and penetrate deeper into the posterior regions and the meatuses where the connections to the sinuses reside.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4628
High Speed Shadowgraphy of Transparent Nozzles as an Evaluation Tool for In-Nozzle Cavitation Behavior of GDI Injectors
Authors: Mamaikin Dmitrii , Knorsch Tobias , Rogler Philipp , Leick Philippe , Wensing Michael
Published: September 2017

Gasoline Direct Injection (GDI) systems have become a rapidly developing technology taking up a considerableand rapidly growing share in the Gasoline Engine market due to the thermodynamic advantages of direct injection. The process of spray formation and propagation from a fuel injector is very crucial in optimizing the air-fuel mixture of DI engines. Previous studies have shown that the presence of some cavitation in high-pressure fuel nozzles can lead to better atomization of the fluid. However, under some very specific circumstances, high levels of cavitation can also delay the atomization process; spray stabilization due to hydraulic flip is the most well-known example. Therefore, a better understanding of cavitation behavior is of vital importance for further optimization of next generation fuel injectors.In contrast to the abundance of investigations conducted on the inner flow and cavitation patterns of diesel injectors, corresponding in-depth research on the inner flow of gasoline direct-injection nozzles is still relatively scarce. In this study, the results of an experiment performed on real-size GDI injector nozzles made of acrylic glass are presented. The inner flow of the nozzle is visualized using a high-power pulsed laser, a long-distance microscope and a high- speed camera. The ambiguity of dark areas on the images, which may represent cavitation regions as well as ambient air drawn into the nozzle holes, is resolved by injecting the fuel both into a fuel or gas filled environment. In addition, the influence of backpressure on the transient flow characteristics of the internal flow is investigated. In good agreement with observations made in previous studies, higher backpressure levels decrease the amount of cavitation inside the nozzles. Due to the high temporal and spatial resolution of the experiment, the transient cavitation behavior during the opening, quasi-steady and closing phases of the injector needle motion can be analyzed. For example, it is found that cavitation patterns oscillate with a characteristic frequency that depends on the backpressure. The link between cavitation and air drawn into the nozzle at the beginning of injection is alsorevealed.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4639
Droplets heating and evaporation: an application to diesel-biodiesel fuel mixtures
Authors: Al Qubeissi Mansour , Al-Esawi Nawar , Sazhin Sergei S
Published: September 2017

The heating and evaporation of automotive fuel droplets are crucial to the design of internal combustion engines and to ensuring their good performance. Accurate modelling is essential to the understanding of these processes and ultimately improving engine design. The interest in fossil-biodiesel fuel blends has been mainly stimulated by depletion of fossil fuels and the need to reduce carbon dioxide emissions that contribute towards climate change. This paper presents an analytical investigation into the application of discrete component model for the heating and evaporation of multi-component fuel droplets to several blended diesel-biodiesel fuels. The model considers the contribution of all groups of hydrocarbons in diesel fuel and methyl esters in biodiesel fuels. The main features of new application to the analysis of blended-fuel droplets in engine-like conditions is described. The model is applied to several blends of diesel, combining 98 components of hydrocarbons, and 19 types biodiesel fuels, combining up to 17 species of methyl ester, considering the differences in their chemical levels of saturation, and thermodynamic and transport properties. One important finding is that some fuel blends, e.g. B5 (5% biodiesel fuel and 95% diesel fuel), can give almost identical droplet lifetimes to the one predicted for pure diesel fuel; i.e. such mixtures can be directly used in conventional diesel engines with minimal, or no, modification to the droplet break-up process.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4644
Spray ignition and local flow properties in a swirled confined spray-jet burner: experimental analysis
Authors: Marrero Santiago Javier , Verdier Antoine , Vandel Alexis , Godard Gilles , Cabot Gilles , Renou Bruno
Published: September 2017

Laser ignition was investigated in the swirled, confined CORIA Rouen Spray Burner under ultra-lean conditions (Φ=0.61) with n-heptane as the liquid fuel. Ignition probability was calculated for different spark locations and compared to the non-ignited local flow properties. Mean velocity components of the carrier flow were measured by PDA under spray presence and without spray, and are compared to mean values from PIV. PIV measurements provide information on the instantaneous airflow and the total strain rate. Fuel droplet size-velocity data was measured by PDA. Toluene-PLIF images were acquired to provide information on the local equivalence ratio and the flammability factor. Results show that the outer recirculation zone (ORZ) has a flammability factor close to 1 and the highest ignition probability (~80%). These results have a high correlation with the air velocity field and turbulent kinetic energy. Instantaneous equivalence ratio images and shear rate-velocity fields give important information on local segregation of the flow properties that help to understand the ignition process. The present work provides a useful database for numerical simulations and industry, plus new insight on spray ignition.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4674
Effect of liquid viscosity on the aerodynamic breakup of non-spherical droplets
Authors: Bergeles Konstantinos , Charalampous Georgios , Hardalupas Yannis , Taylor Alex M.
Published: September 2017

This paper studies the effect of liquid viscosity on the atomisation regimes of initially spherical and non-sphericaldroplets and also kinematic characteristics of non-spherical droplets. The droplets consisted of water-glycerolsolutions with viscosities ranging from 6.3 to 697 mPa s, and the initial aspect ratio was 1<AR<2. The range of Wenumber was from 10 to 200 and of the Oh number from 0.01 to approximately 4. The experimental findings showedthat the equivalent Weeq and Oheq numbers, proposed in previous work [1] for water droplets, are also applicableto spherical and non-spherical droplets in the range of Oh numbers of this study in order to classify the breakupregimes on the existing morphological charts. The kinematic characteristics of the centre of mass for droplets withAR=1.2 are evaluated and the role of viscosity examined in the no breakup and bag-stamen regimes.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4675
Measurement of polymeric time scales from linear drop oscillations
Authors: Plohl Gregor , Brenn Günter
Published: September 2017

The oscillating drop method allows material properties of liquids to be measured from damped drop oscillations. Theliterature discusses, e.g., the measurement of the liquid dynamic viscosity and the surface tension against the ambient medium, predominantly for Newtonian liquids. We use this method for measuring pairs of material properties of polymeric liquids. Pairs of properties may be measured, since the quantity measured is a complex frequency with a real and an imaginary part. For the measurements, individual drops are levitated in air by an ultrasonic levitator and imaged with a high-speed camera. Amplitude modulation of the ultrasound drives shape oscillations of the levitated drop. When the modulation is switched off, with the levitating force maintained, the drop performs free oscillations which are damped due to the liquid viscosity. The data acquired from the images recorded are the angular frequency and the damping rate which are used as an input into the characteristic equation of the oscillating drop. Our measurements intend to yield either two viscoelastic time scales with the zero-shear viscosity known, or one time scale and the zero-shear viscosity, with the other time scale known. The two time scales are the stress relaxation and the deformation retardation times. The latter is difficult to get for polymer solutions.The present contribution presents results from a large set of measurements of the deformation retardation time. Liquids studied are aqueous solutions of poly(acryl-amides) at varying concentration. The corresponding values of the zero-shear viscosity agree well with the values from shear rheometry. Values of the deformation retardation time differ substantially from the values commonly used in viscoelastic flow simulations. Furthermore, the measured values disagree with the predictions from the viscous-elastic stress splitting approach in linear viscoelasticity. With our study we will provide a consistent set of material properties for the Oldroyd-B model in linear viscoelasticity. This will beimportant for material modelling in viscoelastic spray simulations.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4686
Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures
Authors: Stefanitsis Dionisis , Malgarinos Ilias , Strotos George , Nikolopoulos Nikolaos , Kakaras Emmanouil , Gavaises Manolis
Published: September 2017

The present study investigates numerically the aerodynamic breakup of Diesel droplets for a wide range of ambient pressures encountered in engineering applications relevant to oil burners and internal combustion engines. The numerical model solves the Navier-Stokes equations coupled with the Volume of Fluid (VOF) methodology utilized for capturing the interface between the liquid and the surrounding gas. An adaptive local grid refinement technique is used to increase the accuracy of the numerical results around the interface. The Weber (We) numbers examined are in the range of 14 to 279 which correspond to bag, multimode and sheet-thinning breakup regimes. Model results are initially compared against published experimental data and show a good agreement in predicting the drop deformation and the different breakup modes. The predicted breakup initiation times for all cases lie within the theoretical limits given by empirical correlations based on the We number. Following the model validation, the effect of density ratio on the breakup process is examined by varying the gas density (or equivalently the ambient pressure), while the We number is kept almost constant equal to 270; ambient gas pressure varies from 1 up to 146bar and the corresponding density ratios (ε) range from 700 down to 5. Results indicate that the predicted breakup mode of sheet-thinning remains unchanged for changing the density ratio. Useful information about the instantaneous drag coefficient (Cd) and surface area as functions of the selected non-dimensional time is given. It is shown that the density ratio is affecting the drag coefficient, in agreement with previous numerical studies.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4690
Numerical investigation of the role of heat transfer in bubble dynamics
Authors: Fostiropoulos Stavros Rafail , Malgarinos Ilias , Strotos George , Nikolopoulos Nikolaos , Kakaras Emmanouil , Koukouvinis Phoevos , Gavaises Manolis
Published: September 2017

Bubble dynamics is generally described by the well-known Rayleigh-Plesset (R-P) equation in which the bubblepressure (or equivalently the bubble density) is predefined by assuming a polytropic gas equation of state with common assumptions to include either isothermal or adiabatic bubble behaviour. The present study examines the applicability of this assumption by assuming that the bubble density obeys the ideal gas equation of state, while the heat exchange with the surrounding liquid is estimated as part of the numerical solution. The numerical model employed includes the solution of the Navier-Stokes equations along with the energy equation, while the liquid- gas interface is tracked using the Volume of Fluid (VOF) methodology; phase-change mechanism is assumed to be insignificant compared to bubble heat transfer mechanism. To assess the effect of heat transfer and gas equation of state on bubble behaviour, simulations are also performed for the same initial conditions by using a polytropic equation of state for the bubble phase without solving the energy equation. The accuracy of computations is enhanced by using a dynamic local grid refinement technique which reduces the computational cost and allows for the accurate representation of the interface for the whole duration of the phenomenon in which the bubble size changes significantly. A parametric study performed for various initial bubble sizes and ambient conditions reveals the cases for which the bubble behaviour resembles that of an isothermal or the adiabatic one. Additional to the CFD simulations, a 0-D model is proposed to predict the bubble dynamics. This combines the solution of a modified R-P equation assuming ideal gas bubble content along with an equation for the bubbletemperature based on the 1st law of thermodynamics; a correction factor is used to represent accurately the heattransfer between the two phases.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4691
Computational Prediction of Primary Breakup in Fuel Spray Nozzles for Aero-Engine Combustors
Authors: Dauch Thilo Ferdinand , Braun Samuel , Wieth Lars , Chaussonnet Geoffroy , Keller Marc Christoph , Koch Rainer , Bauer Hans-Jörg
Published: September 2017

Primary breakup of liquid fuel in the vicinity of fuel spray nozzles as utilized in aero-engine combustors is numericallyinvestigated. As grid based methods exhibit a variety of disadvantages when it comes to the prediction of multi- phase flows, the ”Smoothed Particle Hydrodynamics“ (SPH)-method is employed. The eligibility of the method to analyze breakup of fuel has been demonstrated in recent publications by Braun et al, Dauch et al and Koch et al [1, 2, 3, 4]. In the current paper a methodology for the investigation of the two-phase flow in the vicinity of fuel spray nozzles at typical operating conditions is proposed. Due to lower costs in terms of computing time, 2D predictions are desired. However, atomization of fluids is inherently three dimensional. Hence, differences between 2D and 3D predictions are to be expected. In course of this study, predictions in 2D and based on a 3D sector are presented.Differences in terms of gaseous flow, ligament shape and mixing are assessed.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4693
Subgrid Liquid Flux and interface modelling for LES of Atomization
Authors: Ahmed Aqeel , Anez Javier , Puggelli Stefano , Reveillon Julien , Brändle de Motta Jorge César , Demoulin François-Xavier
Published: September 2017

Traditional Discrete Particle Methods (DPM) such as the Euler-Lagrange approaches for modelling atomization, even if widely used in technical literature, are not suitable in the near injector region. Indeed, the first step of atomization process is to separate the continuous liquid phase in a set of individual liquid parcels, the so-called primary break-up. Describing two-phase flow by DPM is to define a carrier phase and a discrete phase, hence they cannot be used for primary breakup. On the other hand, full scale simulations (direct simulation of the dynamic DNS, and interface capturing method ICM) are powerful numerical tools to study atomization, however, computational costs limit their application to academic cases for understanding and complementing partial experimental data. In an industrial environment, models that are computationally cheap and still accurate enough are required to meet new challenges of fuel consumption and pollutant reduction. Application of DNS-ICM methods without fairly enough resolution to solve all length scales are currently used for industrial purpose. Nevertheless, effects of unresolved scales are generally cast aside. The Euler-Lagrange Spray Atomization model family (namely, ELSA, also call, Σ−𝑌 or Ω−𝑌) developed by Vallet and Borghi pioneering work [1], and [2], at the contrary aims to model those unresolved terms. This approach is actually complementary to DNS-ICM method since the importance of the unresolved term depends directly on mesh resolution. For full interface resolution the unclosed terms are negligible, except in the far-field spray when the unresolved terms become dominant. Depending on the complexity of the flow and the available computational resources, a Large Eddy Simulation (LES) formalism could be employed as modelling approach. This work focus on the two main terms that drive these different modelling approaches namely the subgrid turbulent liquid flux and the resolved interface. Thanks to the open source library OpenFoam® this work is an attempt to review and to release an adapted modelling strategy depending on the available mesh resolution. For validation, these solvers are tested against realistic experimental data to see the overall effect of each model proposal.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4694
Multi-scale Eulerian-Lagrangian simulation of a liquid jet in cross-flow under acoustic perturbations
Authors: Thuillet Swann , Zuzio Davide , Rouzaud Olivier , Gajan Pierre
Published: September 2017

The design of modern aeronautical propulsion systems is constantly optimized to reduce pollutant emissions whileincreasing fuel combustion efficiency. In order to get a proper mixing of fuel and air, Liquid Jets Injected in gaseous Crossflows (LJICF) are found in numerous injection devices. However, should combustion instabilities appear in the combustion chamber, the response of the liquid jet and its primary atomization is still largely unknown. Coupling between an unstable combustion and the fuel injection process has not been well understood and can result from multiple basic interactions.The aim of this work is to predict by numerical simulation the effect of an acoustic perturbation of the shearing air flow on the primary breakup of a liquid jet. Being the DNS approach too expensive for the simulation of complex injector geometries, this paper proposes a numerical simulation of a LJICF based on a multiscale approach which can be easily integrated in industrial LES of combustion chambers. This approach results in coupling of two models: a two-fluid model, based on the Navier-Stokes equations for compressible fluids, able to capture the largest scales of the jet atomization and the breakup process of the liquid column; and a dispersed phase approach, used for describing the cloud of droplets created by the atomization of the liquid jet. The coupling of these two approaches is provided by an atomization and re-impact models, which ensure liquid transfer between the two-fluid model and the spray model. The resulting numerical method is meant to capture the main jet body characteristics, the generation of the liquid spray and the formation of a liquid film whenever the spray impacts a solid wall.Three main features of the LJICF can be used to describe, in a steady state flow as well as under the effect of the acoustic perturbation, the jet atomization behavior: the jet trajectory, the jet breakup length and droplets size and distribution.The steady state simulations provide good agreement with ONERA experiments conducted under the same condi- tions, characterized by a high Weber number (We>150). The multiscale computation gives the good trajectory of the liquid column and a good estimation of the column breakup location, for different liquid to air momentum flux ratios. The analysis of the droplet distribution in space is currently undergoing. A preliminary unsteady simulation was able to capture the oscillation of the jet trajectory, and the unsteady droplets generation responding to the acousticperturbation.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4697
Planar droplet sizing: Application to a spray of Jet A1 kerosene
Authors: Doublet Pierre , Lempereur Christine , Bodoc Virginel , Orain Mikael , Gajan Pierre
Published: September 2017

Optical techniques are  widely employed for their non-intrusive behavior and are applied to two-phase flowinvestigations. Until now, the most commonly used technique to determine the droplet size is the Phase Doppler Anemogranulometry, although it is time consuming for an overall injector characterization. An imaging technique called Planar Droplet Sizing has been used to offer an alternative and provide a spatially-resolved 2D map of the Sauter Mean Diameter (SMD). The measurement is based on the ratio between laser-induced fluorescence and scattered light intensities which are assumed to be proportional respectively to the droplet volume and droplet surface area. However, previous studies revealed that the dependence of fluorescence intensity on the droplet volume can be altered by the absorption of light in the liquid. The scattered light intensity depends on the scattering angle and intensity variations within the field of view must be avoided.The aim of this study is to make the PDS technique operational for a Jet A-1 kerosene spray. A strong absorption of liquid kerosene appears under UV excitation at 266 nm making the technique unsuitable. Under visible excitation at 532 nm, a fluorescent tracer (Pyrromethene 597) must be added to the kerosene to enhance the fluorescence signal. To prevent scattered light intensity variations within the field of view, an optimal scattering angle close to 115° is required. An image processing algorithm is proposed in order to reduce the effects ofmultiple scattering.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4698
Behaviour of free falling viscoelastic liquid jets
Authors: Tirel Christophe , Renoult Marie-Charlotte , Dumouchel Christophe , Blaisot Jean-Bernard
Published: September 2017

In a recent work, a protocol to measure the relaxation time of dilute polymer solutions, known to be challenging,has been established [1]. This protocol is based on a 2D multi-scale description of free-falling low velocity viscoelastic liquid jets. Although the relaxation time reached an asymptotic value for high jet velocities, a significant dependence with the jet velocity is observed for low velocities. The present work reconsiders these previous experimental data using a 3D multi-scale analysis in order to identify the origin of the dependence between the relaxation time and the jet velocity. The 3D analysis demonstrates the importance of a velocity–dependent coalescence mechanism in the jet behaviour. Thanks to a simple model of jet deformation it is demonstrated that this coalescence mechanism prevents the elasto-capillary contraction of the smallest scales from occurring whenthe jet velocity is reduced.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4700
X-ray diagnostics of dodecane jet in spray A conditions using the new one shot engine (NOSE)
Authors: Hugo Ajrouche , Ibrahim Chiboub , Ob Nilaphai , Sébastien Dozias , Bruno Moreau , Camille Hespel , Fabrice Foucher , Christine Mounaïm-Rousselle , Jean-Michel Pouvelse , Eric Robert
Published: September 2017

Quantifying liquid mass distribution data in the dense near nozzle area to develop and optimize diesel spray byoptical diagnostic is challenging. Optical methods, while providing valuable information, have intrinsic limitations due to the strong scattering of visible light at gas-liquid boundaries. Because of the high density of the droplets near the nozzle, most optical methods are ineffective in this area and prevent the acquisition of reliable quantitative data. X-ray diagnostics offer a solution to this issue, since the main interaction between the fuel and the X-rays is absorption, rather than scattering, thus X-ray technique offers an appealing alternative to optical techniques for studying fuel sprays. Over the last decade, x-ray radiography experiments have demonstrated the ability to perform quantitative measurements in complex sprays. In the present work, an X-ray technique based on X-ray absorption has been conducted to perform measurements in dodecane fuel spray injected from a single-hole nozzle at high injection pressure and high temperature. The working fluid has been doped with DPX 9 containing a Cerium additive, which acts as a contrast agent. The first step of this work was to address the effect of this dopant, which increases the sensitivity of X-ray diagnostics due its strong photon absorption, on the behavior and the physical characteristics of n-dodecane spray. Comparisons of the diffused back illumination images acquired from n- dodecane spray with and without DPX 9 under similar operating conditions show several significant differences. The current data show clearly that the liquid penetration length is different when DPX 9 is mixed with dodecane. To address this problem, the dodecane was doped with a several quantities of DPX containing 25% ± 0.5 of Cerium. Experiments show that 1.25% of Ce doesn’t affect the behaviour of spray. Radiography and density measurements at ambient pressure and 60 bars are presented. Spray cone angle around 5° is obtained. The obtained data shows that the result is a compromise between the concentration of dopant for which the physical characteristics of thespray do not change and the visualization of the jet by X-ray for this concentration.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4705
Weakly nonlinear instability of a viscous liquid jet
Authors: Brenn Günter , Renoult Marie-Charlotte , Mutabazi Innocent
Published: September 2017

Aweakly nonlinear stability analysis of an axisymmetric viscous liquid jet is performed. The calculation is based ona small-amplitude perturbation method and restricted to second order. Contrary to the inviscid jet and the planar viscous sheet cases studied by Yuen in 1968 [1] and Yang et al. in 2013 [2], respectively, a part of the solution results from a polynomial approximation of Bessel functions. Results on interface shapes for a small wave number and initial perturbation amplitude, four different Ohnesorge numbers, taking into account the approximate part or not, are used to predict the influence of liquid viscosity on satellite drop formation and evaluate the influence of the approximation. It is observed that the liquid viscosity has a retarding effect on satellite drop formation, in agreement with previous experimental and numerical work. In addition, it is found that the approximate terms can be reasonably ignored, providing a simpler viscous weakly nonlinear model for the description of the first nonlinearity growth in liquid jets.The present work replaces the ILASS 2016 paper [3] by the authors on the same subject.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4711
Modelling and validation of near-field Diesel spray CFD simulations based on the Σ -Y model
Authors: Pastor J.M. , Desantes J.M. , García-Oliver J.M. , Pandal A. , Naud B. , Matusik K. , Duke D. , Kastengren A. , Powell C. , Schmidt D.P.
Published: September 2017

Diesel spray modelling still remains a challenge, especially in the dense near-nozzle region. This region is difficultto experimentally access and also to model due to the complex and rapid liquid and gas interaction. Modelling approaches based on Lagrangian particle tracking have struggled in this area, while Eulerian modelling has proven particularly useful. An interesting approach is the single-fluid diffuse interface model known as Σ-Y, based on scale separation assumptions at high Reynolds and Weber numbers. Liquid dispersion is modelled as turbulent mixing of a variable density flow. The concept of surface area density is used for representing liquid structures, regardless of the complexity of the interface.In this work, an implementation of the Σ-Y model in the OpenFOAM CFD library is applied to simulate the ECN Spray A in the near nozzle region, using both RANS and LES turbulence modelling. Assessment is performed with measurements conducted at the Advanced Photon Source at Argonne National Laboratory (ANL). The ultra-small- angle x-ray scattering (USAXS) technique has been used to measure the interfacial surface area, and x-rayradiography to measure the fuel dispersion, allowing a direct evaluation of the Σ-Y model predictions.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4715
Multiple Impinging Jet Air-Assisted Atomization
Authors: Costa Mário , Pizziol Bruno , Panao Miguel , Silva André
Published: September 2017

The growth of the aviation sector triggered the search for alternative fuels and continued improvements in thecombustion process. This work addresses the technological challenges associated with spray systems and theconcern of mixing biofuels with fossil fuels to produce alternative and more ecological fuels for aviation. This workproposes a new injector design based on sprays produced from the simultaneous impact of multiple jets, using anadditional jet of air to assist the atomization process. The results evidence the ability to control the average dropsize through the air-mass flow rate. Depending on the air-mass flow rate there is a transition between atomizationby hydrodynamic breakup of the liquid sheet formed on the impact point, to an aerodynamic breakup mechanism,as found in the atomization of inclined jets under cross-flow conditions. The aerodynamic shear breakupdeteriorates the atomization performance, but within the same order of magnitude. Finally, our experiments showthat mixing a biofuel with a fossil fuel does not significantly alter the spray characteristics, regarded as a stepfurther in developing alternative and more ecological fuels for aero-engines.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4737
Study of the soot quantification for two-stage injection of hydrogenated catalytic biodiesel in a constant-volume combustion chamber
Authors: Jiawei Cao , Zhixia He , Bei Li , Wenjun Zhong , Mei Wang
Published: September 2017

The effect of two-stage injection strategies on the soot formation of 0# fossil diesel were investigated experimentally using a constant volume combustion chamber. The ambient conditions was kept constant as injection pressure 150 MPa, ambient gas temperature 900 K, ambient gas pressure 45 bar. A high-speed diffused back-illumination extinction imaging technique was employed to make quantitative measurement on temporal soot evolution and reacting spray liquid length and a direct high-speed camera was used to measure the ignition delay. Two-stage injection strategies were varied with different pilot and main injection time, including a sweep of dwell time in pilot-main injection and pilot injection duration. The results show that the ignition delay decreases with the increasing dwell time. It may result from the entrained surrounding gas enhance the spray combustion process. In the reacting condition, the liquid-phase penetration is slightly longer with the shorter dwell time. However, the pilot injection duration shows slighter impact. The longer dwell time contributes to more total soot mass while the different pilot injection duration barely affect the total soot mass of the main injection.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4739
Quantification of diesel injector dribble using 3D reconstruction from x-ray and DBI imaging
Authors: Crua Cyril , Sechenyh Vitaliy , Turner Jack , Sykes Dan , Duke Daniel J , Swantek Andrew B , Matusik Katarzyna E , Kastengren Alan , Powell Christopher , Viera Alberto , Payri Raul
Published: September 2017

Post-injection dribble is known to lead to incomplete atomisation and combustion due to the release of slowmoving, and often surface-bound, liquid fuel after the end of the injection event. This can have a negative effect on engine emissions, performance, and injector durability. To better quantify this phenomenon we present a new image processing approach to quantify the volume and surface area of ligaments produced during the end of injection, for an ECN ‘Spray B’ 3-hole injector. Circular approximation for cross-sections was used to estimate three-dimensional parameters of droplets and ligaments. The image processing consisted in three stages: edge detection, morphological reconstruction, and 3D reconstruction. For the last stage of 3D reconstruction, smooth surfaces were obtained by computation of the alpha shape which represents a bounding volume enveloping a set of 3D points. The object model was verified by calculation of surface area and volume from 2D images of figures with well-known shapes. We show that the object model fits non-spherical droplets and pseudo-cylindrical ligaments reasonably well. We applied our processing approach to datasets generated by different research groups to decouple the effect of gas temperature and pressure on the fuel dribble process. High-speed X-ray phase-contrast images obtained at room temperature conditions (297 K) at the 7-ID beamline of the Advanced Photon Source at Argonne National Laboratory, together with diffused back-illumination (DBI) images captured at a wide range of temperature conditions (293-900 K) by CMT Motores Térmicos, were analysed and comparedquantitatively.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4742
Visualization of pilot flame of an optically-accessible coaxially-staged aero-engine lean-burn fuel injector
Authors: Matsuura Kazuaki , Uesaka Shunya , Iwasaki Tomoyuki , Kurosawa Yoji , Yamada Hideshi , Yamamoto Takeshi , Hayashi Shigeru
Published: September 2017

The visualization of the pilot flame of a coaxially-staged aero-engine lean-burn fuel injector, not only downstreambut also inside of the pilot nozzle, was successfully performed at realistic aero-engine conditions. Optical access toward the inside of the nozzle was achieved through the inner and outer shrouds, both of which were made of transparent quartz. The image distortion caused by complex contours of the two shrouds was corrected by a method based on optical ray tracing, which realized precise determination of spatial intensity distribution of optical signals. Line-of-sight OH chemiluminescence, cross-sectional OH-LIF, kerosene LIF and kerosene Mie scattering were employed as diagnostic tools. The effects of pilot local air-to-fuel ratio on spray flame structure were revealed, both inside and downstream of the pilot nozzle under stable combustions. As the pilot mixture got rich, the main reaction zone moved from inside of the pilot nozzle to the region near the injector lip downstream of the injector exit. The OH-LIF signal was detected near the central axis surrounded by the fuel spray. It was also observed near the back-step of the pilot nozzle for the rich cases. The experiments under combustion oscillation were also conducted and the correlation of phenomena inside and downstream of the pilot nozzle was captured. It was clarified that the reaction enhancement in the outer part of the lip vortex region was caused by the convectionof rich mixture, which appeared near the pilot atomizer lip at 150~210deg earlier oscillation phase angle.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4752
Simulation of droplet spreading on micro-CT reconstructed 3D real porous media using the volume-of-fluid method
Authors: Aboukhedr Mahmoud , Mitroglou Nicholas , Georgoulas Anastasios , Marengo Marco , Vogiatzaki Konstantina
Published: September 2017

Droplet impact on porous media has a broad range of applications such as material processing, drug deliveryand ink injection etc. The simulation studies of such processes are rather limited. To represent the spreading and absorption process of the droplet on porous materials, robust numerical schemes capable of accurately representing wettability as well as capillary effects need to be established. The current work, presents one of the first studies of droplet impact on a real porous media geometry model extracted from a micro-CT scan. The process involves processing of CT image and subsequent threshold based on the structures segmentation. The porous geometry is extracted in the form of a STL (STereoLithography) model, which, with the aid of dedicated software like ANSA and SnappyHexMesh, is converted to an unstructured mesh for successful discretization of the flow domain. The solution algorithm is developed within the open source CFD toolbox OpenFOAM. The numerical framework to track the droplet interface during the impact and the absorption phases is based on previous work [1, 2]. The volume-of-fluid (VOF) method is used to capture the location of the interface, combined with additional sharpening and smoothing algorithms to minimise spurious velocities developed at the capillary dominated part of the phenomenon (droplet recession and penetration). A systematic variation of the main factors that affect this process are considered, i.e. wettability, porous size, impact velocity. To investigate the influence of porous structures on droplet spreading, the average porosity of the media is varied between 18.5% and 23.3% . From these numerical experiments, we can conclude that the droplet imbibition mainly depends on the porous wettability and secondly that the recoiling phasecan be observed in the hydrophobic case but not in the hydrophilic case.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4755
Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions
Authors: Traxinger Christoph , Müller Hagen , Pfitzner Michael , Baab Steffen , Lamanna Grazia , Weigand Bernhard , Matheis Jan , Stemmer Christian , Adams Nikolaus A. , Hickel Stefan
Published: September 2017

Experiments and numerical simulations were carried out in order to contribute to a better understanding and predic-tion of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation processes of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a chamber filled with pure nitrogen at 5 MPa and 293 K and three different test cases were selected such that they cover regimes in which the thermodynamic non-idealities, in particular the effects that stem from the potential phase separation, are significant. Simultaneous shadowgraphy and elastic light scattering experiments were conducted to capture both the flow structure as well as the phase separation. In addition, large-eddy simulations with a vapor- liquid equilibrium model were performed. Both experimental and numerical results show phase formation for the cases, where the a-priori calculation predicts two-phase flow. Moreover, qualitative characteristics of the formation process agree well between experiments and numerical simulations and the transition behaviour from a dense-gasto a spray-like jet was captured by both.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4756
The liquid penetration of diesel substitutes
Authors: Weiss Lukas , Riess Sebastian , Rezaei Javad , Peter Andreas , Wensing Michael
Published: September 2017

Diesel fuel consist of several hundreds of substances on organic basis. Experimental and numerical investigationsof this multicomponent fuel are hard to interpret in detail, since the behavior of the multicomponent mixture is complex. Physical and chemical data of this system is not available under engine relevant conditions. Instead, fundamental research substitutes diesel with pure substances, where a big database exists.Prior work already showed, that overall spray propagation (including vapor phase) is nearly independent on the injected fuel. This is due to the high air entrainment at present diesel engine conditions (very high injection pressure and dense ambient atmosphere). The high air entrainment shortly behind the nozzle exit (within the first 5 mm penetration) creates a situation where properties of the ambient gas dominate the spray propagation resulting in similar mass and momentum distributions even for different fuels, if the injection conditions are kept constant. On the other hand, the liquid length is clearly different for different fuels, so that location and time of the phase change differ with consequences on the time available for mixture formation in the gas phase. The paper describes the liquid length as a function of the enthalpy necessary for the phase transition (given by the fuel and fuel temperature at injection) and the injection conditions (ambient gas properties, injector design and injection pressure). We compare two different models describing the enthalpy balance. Siebers et al. presented “Model I”, where mass transfer dominates the enthalpy transfer and evaporation takes place. In our own “Model II” evaporation is suppressed, resulting in a heat transfer driven enthalpy transfer without mass transport. The calculations are validated with experimental data.The liquid length is optically accessible by Mie-Scattering imaging techniques, the complete spray evolution by Schlieren technique. The experimental study was carried out in the high-pressure combustion vessel “OptiVeP” at FAU. The data shown in this paper derived from measurements with dodecane injected at 1200 bar into 613 K ambient. The ambient pressure varies from 1 – 10 MPa. A Continental research injector with a 115 µm hole and L/D of 6.5 was used. Nitrogen atmosphere suppressed ignition.Increasing the ambient pressure leads to a change in the mechanism in phase transition. It switches from a masstransfer dominated regime to a heat transfer dominated regime at high ambient pressures.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4764
A study on the relationship between internal nozzle geometry and injected mass distribution of eight ECN Spray G nozzles.
Authors: Matusik Katarzyna E , Duke Daniel J , Sovis Nicholas , Swantek Andrew B , Powell Christopher F , Payri Raul , Vaquerizo Daniel , Giraldo-Valderrama Sebastian , Kastengren Alan L
Published: September 2017

Gasoline direct injection (GDI) nozzles are manufactured to meet geometric specifications with length scales onthe order of a few hundred microns. The machining tolerances of these nominal dimensions are not always knowndue to the difficulty in accurately measuring such small length scales in a nonintrusive fashion. To gain insight intothe variability of the machined dimensions as well as any effects that this variability may have on the fuel spraybehavior, a series of measurements of the internal geometry and fuel mass distribution were performed on a set ofeight nominally duplicate GDI “Spray G” nozzles provided by the Engine Combustion Network. The key dimensionsof each of the eight nozzle holes were measured with micron resolution using full spectrum x-ray tomographicimaging at the 7-BM beamline of the Advanced Photon Source at Argonne National Laboratory. Fuel densitydistributions at 2 mm downstream of the nozzle tips were obtained by performing x-ray radiography measurementsfor many lines of sight. The density measurements reveal nozzle-to-nozzle as well as hole-to-hole density variations.The combination of high-resolution geometry and fuel distribution datasets allows spray phenomena to be linked tospecific geometric characteristics of the nozzle, such as variability in the hole lengths and counterbore diameters,and the hole inlet corner radii. This analysis provides important insight into which geometrical characteristics ofthe nozzles may have the greatest importance in the development of the injected sprays, and to what degreethese geometric variations might account for the total spray variability. The goal of this work is then to further theunderstanding of the relationship between internal nozzle geometry and fuel injection, provide input to improvecomputational models, and ultimately aid in optimizing injector design for higher fuel efficiency and lower emissionsengines.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4766