bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental study of liquid-vapor mass transfer in non-reacting and reacting droplet chains
Authors: Stöhr Michael , Werner Stefanie , Meier Wolfgang 
Published: September 2017

The dynamics of liquid-vapor mass transfer largely determines the performance of internal and gas turbine spraycombustors. The key mechanisms however typically take place on small spatial scales of less than 100 μm which have been difficult to measure. The present work thus aims at the development and application of an experimental technique for the characterization of droplet evaporation with high spatial resolution. Single chains of monodisperse acetone droplets with diameters of 125 and 225 μm are injected into a channel with a cross-section of 60x60 mm² and quartz glass side walls for optical access. The droplet chains are surrounded by a laminar air flow with velocity and temperature of about 0.1 m/s and 300 K, respectively. The distribution of acetone vapor around the droplets is measured using planar laser-induced fluorescence (PLIF) excited by the 4th harmonic of a Nd:YAG laser at 266 nm. The measurements are performed in thin transversal sections between the droplets in order to avoid signal corruption by halation effects that occur when the laser directly hits the droplets as reported in previous studies. In addition, the spatial resolution of the PLIF setup was enhanced by using proper sheet- forming and imaging optics. The resulting in-plane resolution and out-plane-resolution (i.e. thickness of the laser sheet) are both determined to about 20 μm, which thus allows an accurate characterization of the small-scale vapor distribution near the droplets. Using a separate calibration measurement, quantitative acetone concentrations are obtained for non-reacting conditions. As a complementary technique, the droplet evaporation is measured using shadowgraphy droplet sizing. Both non-reacting and reacting droplet chains are studied. The results for the non-reacting cases show that the droplet chains are surrounded by a column of nearly-saturated acetone vapor with a concentration maximum at the centerline. For increasing radial distances, the vapor concentration decays quickly with a half width of 0.5 mm and reaches almost zero for r&gt;1 mm. It is further seen that the width of the vapor column increases with streamwise distance. For the experiment with a reacting droplet chain, which is continuously ignited by a heating wire at the channel inlet, a cylindrical reaction zone around the chain with a radius of about 1.5 mm is observed. The shadowgraphy measurements show that the rate of droplet evaporation is significantly enhanced for the reacting conditions. This is attributed to the high rate of heat transfer from the flame to the droplets and the resulting enhanced acetone mass transfer to the sink at the reaction zone.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4767
Energy Aspects in Spray Formation by Homogenous Flash Boiling Process
Authors: Moshkovich Yahav , Levy Yeshayahou , Sher Ilai , Sher Eran 
Published: September 2017

When a pressurized bubbly mixture is driven out through an orifice, the mixture pressure abruptly drops and thebubbles undergo a rapid expansion process, which under some circumstances results in a rapid disintegration of the liquid bulk into small droplets (atomization). Depending on the initial conditions, heterogeneous or homogeneous nucleation of vapor bubbles may occur. For homogeneous nucleation, the vapor bubbles grow rapidly one towards the other, and when they touch each other the bubbles “explode”. In this stage, the liquid around the bubbles is teared, and a spray with small and uniform droplets is formed. In the literature, it seems that the efficiency of the homogenous flash boiling process is very low. In this work, we analyse this process andanalyse it for possible energy losses.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4773
Influence of the Fuel Properties on the Injection Process and Spray Development in a large ship diesel Engine
Authors: Najar Ibrahim , Buchholz Bert , Stengel Benjamin , Fink Christian , Hassel Egon 
Published: September 2017

The present paper deals with the influence of fuel properties on the spray behaviour. This influence was studiedexperimentally using a common rail injection system from a medium speed diesel engine. The experiments have been performed with diesel fuel (EN-590) and heavy fuel oil (RMG 180) on a constant volume chamber at room temperature. Comparison of the spray characteristics shows that the heavy fuel oil penetrates deeper in the chamber. However, the diesel spray has a bigger cone angle. These results formed the basis for a further development of the 1D-model [1] to predict the spray penetration by considering the fuel properties and temperature.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4787
High speed visualization of gasoline pump injector (GPI)
Authors: Balasubramanian Nallannan , Iwaszkiewicz Titus , Sethuraman Jayabalan 
Published: September 2017

Two-wheeler engines still use carburetor as a fuelling system in many Asian countries, owing to its low cost andless maintenance. The usage of carburetor to handle the upcoming stringent emission norms gets difficult, due to the absence of a closed-loop fuel correction. An electronic fuel injector (EFI), on the other hand, with the help of an electronic control unit (ECU), can correct the fuel quantity and set the air-fuel mixture close to stoichiometric, based on the feedback obtained from the oxygen sensor placed in the exhaust pipe. In this context, an innovative injection system has been developed, that can be applied for such electronic fuel injection in two-wheelers. In this design, the pump and injector are integrated into a single unit, making the system, simple, compact and less expensive. The integrated injector uses a solenoid and spring arrangement, for pressurizing the fuel in a small chamber, and the pressurized fuel is then injected through orifices to produce spray in the intake port. Two-wheeler engines can operate in the order of 10,000 rpm and it poses a big challenge in such injector designs, and therefore the time response of the mechanical and magnetic components of the injector become critical. High-speed back-lit imaging helps in understanding the time response of such injector, by visualizing the spray, while injecting continuously over a period of time. This paper presents the results of high-speed images, obtained from the spray of this new-concept gasoline pump injector (GPI). This exercise, demonstrated that this injector can work at a frequency as high as 83 Hz and also consistently. The spray pattern was found to be very unique and different from the conventional PFIinjection sprays.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4796
Flexible Piezoelectric Drop-On-Demand Droplet Generation
Authors: Riefler Norbert , Wriedt Thomas , Fritsching Udo 
Published: September 2017

The size of droplets generated by piezoelectric drop-on-demand (DOD) droplet generators can be varied to a cer-tain degree within one order of magnitude. This variation means that the droplet size is not solely determined by the nozzle diameter, and the droplet generation process is not restricted to drops extruded through a nozzle in conven- tional operation. By varying the electronic driving pulse, different droplet sizes can be obtained. To investigate the interaction of piezoelectric pulse excitation and the finally produced droplets, different approaches are applied. A comparison of a modal analysis of a pure piezo based on mechanical admittance calculations proofs the usability of electrical impedance measurements. This kind of measurements are then compared to finite-element simulations of a coupled piezo system – one as actuator, the other as pressure sensor – to extend the usable methods with the result that the fluid is of minor influence on the modal frequencies. Last, two phase fluid flow simulations with consequent pressure wave evaluations of the fluid show different pressure wave frequency specta than the modalanalysis.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4846
Drop Impact onto a Metallic Porous Layer: Effect of Liquid Viscosity and Air Entrapment
Authors: Boscariol Cristina , Sarker Dipak , Kang Boseon , Crua Cyril , Marengo Marco 
Published: September 2017

The drop impact onto porous surfaces has important applications in many fields, such as painting, paper coating,drug delivery and cosmetic sprays. In most of these applications, the optimisation of the deposition process is carried out empirically, without a proper understanding of the physics and a theoretical modelling of the spreading and the imbibition phenomena. The purpose of this study is to analyse droplet impacts on metallic meshes to define a general modelling strategy of the impact regimen on particular 2D regular porous surfaces. The application of this structure is relevant in process like filtration but also in the medical field, considering for example reconstructive surgery. By analysing the impact of droplets of water, acetone and a mixture of glycerol and water, having a diameter and an impact velocity in a range of 1.5-3mm and 2-4m/s, respectively, on meshes with a pore size ranging between 25 and 400 µm, a regime map was built considering 6 different impact outcomes. The outcomes were characterised by a deposition of the droplet on the substrate, or a partial imbibition, or a total imbibition. By increasing the impact velocity, a splash region was defined, which is still characterised by a final deposition, a partial imbibition and a total imbibition. It is found that the most influencing parameters are closely linked to the liquid properties and the impact velocity, more specifically liquid surface tension plays a major role in defining the impact outcome. In the case of Acetone, the lower surface tension brings to an almost instantaneous total imbibition whereas the experiments conducted using water and glycerol solution, showed a major distribution of the deposition regimes with respect to the other outcomes, due to the effect of a higher viscosity. It was found that the geometrical characteristics of the mesh such as pore size and wire diameter, play an important role as well in defining the total imbibition outcome. Finally, the defined transition maps, shows that for a certain combination of physical properties and initial condition,the outcome of the droplet impact is predictable.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4973
VOF Simulation of The Cavitating Flow in High Pressure GDI Injectors
Authors: Giussani Filippo , Montorfano Andrea , Piscaglia Federico , Onorati A. , Helie Jerome 
Published: September 2017

The paper describes the development in the OpenFOAM® technology of a dynamic multiphase Volume-of-Fluid (VoF) solver, supporting mesh handling with topological changes, that has been used for the study of the physics of the primary jet breakup and of the flow disturbance induced by the nozzle geometry during the injector opening event in high-pressure Gasoline Direct Injection (GDI) engines. Turbulence modeling based on a scale-resolving approach has been applied, while phase change of fuel is accounted by means of a cavitation model that has been coupled with the VOF solver. Simulations have been carried out on a 6-hole prototype injector, especially developed for investigations in the framework of the collaborative project FUI MAGIE and provided by Continental Automotive SAS. Special attention has been paid to the domain decomposition strategy and to the code development of the solver, to ensure good load balancing and to minimize inter-processor communication, to achieve good performanceand also high scalability on large computing clusters.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4989
Visualization of water droplet deformation and breakup in a continuously accelerating flow field
Authors: Garcia-Magariño Adelaida , Sor Suthyvann , Velazquez Angel 
Published: September 2017

A new specific direct illumination technique is proposed for studying the deformation and breakup process ofdroplets that are exposed to a continuously increasing flow field. This type of flow field is in contrast to the traditional shock-tube experiments where droplets are suddenly exposed to a constant high airstream. In order to generate a continuously accelerated flow field the rotating arm facility at INTA is used. Droplets are allowed to fall in the path of an incoming airfoil mounted at the end of a rotating arm. Under certain conditions, these droplet deform and breakup before impinging on the airfoil. The incoming airfoil is a key element in the illumination technique. Droplets of 0.8 mm of diameter immersed in the flow field generated by an airfoil model of chord 0.690m approaching at 80 m/s were chosen for this study and were found to undergo a breakup process similar to the bag and stamen breakup found in the literature. Each of the stages at this type of breakup process was investigated by means of this new direct illumination technique and a high resolution camera. These images were compared to those images obtained using shadowgraph illumination technique and a high speed camera under the same conditions. Five different stages were studied and characterized. The final objective in this study was to visualize and identify fluid structures that occur during the deformation and breakup process in a continuouslyaccelerated flow field in order to develop and fine tune physical-mathematical models.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4991
Spreading model for wall films generated by high-pressure sprays
Authors: Lamarque Nicolas , Lamiel Quentin , Hélie Jérome , Legendre Dominique 
Published: September 2017

This paper presents a new model developed to predict the area of wall films that may develop in gasoline direct injection engines (GDI). In a always more restrictive legislation on gas emissions the injection process in internal combustion (IC) engines has been highlighted as a domain of great concern in order to satisfy these requirements. Many spray wall interactions models exist in literature and are included in different CFD tools. Most often they are based on the sum of single drop-wall impacts. The specificity of the present model lies in its simplicity and the way the film is treated globally. Here its propagation is predicted using a balance between the momentum given by the spray and the viscous shear stress. Jointly with the theoretical model, an experimental set-up has been built up, an optical measurement technique called Refractive Index Matching method is used to follow the development of the wall film.It has been found that the area of the wall film is proportional to the duration of injection, while the distance betweenthe injector and the wall has not shown many influence on the evolution of area. The influence of the injection pressure has also been identified, when the pressure is doubled the radius of the film is multiplied by 3√2. Eventuallyedicts that film thickness decreases as fuel pressure rises.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4999
Characterization of Liquid Impinging Jet Injector Sprays for Bi-Propellant Space Propulsion: Comparison of PDI and High-Magnification Shadowgraphy
Authors: Boust Bastien , Michalski Quentin , Claverie Alain , Indiana Clément , Bellenoue Marc 
Published: September 2017

Impinging jet sprays are investigated in the reference case of like-doublet injector, for application to bi-propellantcombustion. Green propellants are considered, namely ethanol as a fuel and hydrogen peroxide as an oxidizer, that is well represented by water. This study reports original comparisons between standard spray characterization (PDI) and high-magnification shadowgraphy of the spray (2.5 x 3.2 mm, 2.5 µm per pixel) based on short laser backlight illumination (5 ns). Shadowgraphy images describe accurately the inner spray structure and provide the size and velocity of droplets. This diagnostic is used to analyse the influence of jet momentum (driven by injection pressure) on impinging jet atomization, as well as the evolution of spray topology, drop size distribution and average diameter along the spray centreline. The application of shadowgraphy to the dense region of water and ethanol sprays shows the different atomization behaviour of these two fluids with respect to their surface tension. Elliptical droplets are characterized inside the spray, which confirms the interest of a direct visualization of droplets in suchdense sprays.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5001
Experimental and numerical study on sensible heat transfer at droplet/wall interactions
Authors: Moita Ana Sofia , Teodori Emanuele , Pontes Pedro , Moreira António Luís Nobre , Georgoulas Anastasios , Marengo Marco 
Published: September 2017

The present study addresses a detailed experimental and numerical investigation on the impact of water dropletson smooth heated surfaces. High-speed infrared thermography is combined with high-speed imaging to couple the heat transfer and fluid dynamic processes occurring at droplet impact. Droplet spreading (e.g. spreading ratio) and detailed surface temperature fields are then evaluated in time and compared with the numerically predicted results. The numerical reproduction of the phenomena was conducted using an enhanced version of a VOF- based solver of OpenFOAM previously developed, which was further modified to account for conjugate heat transfer between the solid and fluid domains, focusing only on the sensible heat removed during droplet spreading. An excellent agreement is observed between the temporal evolution of the experimentally measured and the numerically predicted spreading factors (differences between the experimental and numerical values were always lower than 3.4%). The numerical and experimental dimensionless surface temperature profiles along the droplet radius were also in good agreement, depicting a maximum difference of 0.19. Deeper analysis coupling fluid dynamics and heat transfer processes was also performed, evidencing a strong correlation between maximum and minimum temperature values and heat transfer coefficients with the vorticity fields in the lamella, which lead to particular mixing processes in the boundary layer region. The correlation between the resulted temperature fields and the droplet dynamics was obtained by assuming a relation between the vorticity and the local heat transfer coefficient, in the first fluid cell i.e. near the liquid-solid interface. The two measured fields revealed that local maxima and minima in the vorticity corresponded to spatially shifted local minima and maxima in the heat transfer coefficient, at all stages of the droplet spreading. This was particularly clear in the rim region,which therefore should be considered in future droplet spreading models.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5024
Direct numerical simulation of an atomizing biodiesel jet: Impact of fuel properties on atomization characteristics
Authors: Ling Yue , Legros Guillaume , Popinet Stéphane , Zaleski Stéphane 
Published: September 2017

The utilization of biodiesel is an effective approach to reduce pollution from internal combustion engines and thushas attracted steadily increasing interest in the recent years. As the viscosity of biodiesel is much higher than that of standard diesel, the atomization characteristics of a biodiesel jet can significantly deviate from those of a standard diesel jet under identical injection conditions. Since atomization of the injected fuel has a strong impact on fuel-air mixing and the following combustion processes, it is important to investigate the atomization of biodiesel and in particular to understand how the fuel properties affect the atomization process and the resulting spray character- istics. In the present study, three-dimensional direct numerical simulations are conducted to investigate atomizing biodiesel and diesel jets. The novel adaptive multiphase solver Basilisk is used for simulations. The statistics ofdroplets formed in the biodiesel jet is compared to the diesel jet under identical injection conditions.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5035
Binary cavitation in a transparent three hole GDI nozzle
Authors: Chaves Humberto , Donath Sebastian 
Published: September 2017

A more or less real size three hole (0.1 mm diameter) transparent injection nozzle was made with 120° betweenthe orifices and an inclination of 20° to the injector axis. The geometry is similar to that of a multi hole GDI injector. Experiments are performed using n-pentane and α-methyl-naphtalene mixtures in varying composition. The flow in the orifices is observed under submerged injection conditions from downstream looking in direction of the injector using a beam splitter plate for illumination with the light from a Minilite NdYag laser that was made incoherent by fluorescence in a cuvette filled with a dilute rhodamine-ethanol mixture. The images show the appearance of cavitation depending on the cavitation number as well as on the composition of the mixture. The behaviour is not what can be expected from equilibrium thermodynamics. Due to the transient nature of the flow the n-pentane concentration cannot attain the equilibrium value one would expect and cavitation occurs at highercavitation values. Diffusion appears to play a role in the onset appearance of cavitation for binary mixtures.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5051
Transcritical mixing of sprays for multi-component fuel mixtures
Authors: Manin Julien , Crua Cyril , Pickett Lyle M. 
Published: September 2017

The mixing of fuels with oxidizer has been an increasingly interesting area of research with new engine technologiesand the need to reduce emissions, while leveraging efficiency. High-efficiency combustion systems such as diesel engines rely on elevated chamber pressures to maximize power density, producing higher output. In such systems, the fuel is injected under liquid state in a chamber filled with pressurized air at high temperatures. Theoretical calculations on the thermodynamics of fuel mixing processes under these conditions suggest that the injected liquid can undergo a transcritical change of state. Our previous experimental efforts in that regard showed through high- speed imaging that spray droplets transition to fluid parcels mixing without notable surface tension forces, supporting a transcritical process. Only mono-component fuels were used in these studies to provide full control over boundary conditions, which prevented extrapolation of the findings to real systems in which multi-component fuels are injected. Multi-component fuels add another layer of complexity, especially when detailed experiments serve model development, requiring the fuels to be well characterized. In this work, we performed high-speed microscopy in the near-field of high-pressure sprays injected into elevated temperature and pressure environments. A reference diesel fuel and several multi-component surrogates were studied and compared to single component fuels. The results support that a transition occurs under certain thermodynamic conditions for all fuels. As anticipated, the transition from classical evaporation to diffusive mixing is affected by ambient conditions, fuel properties, droplet size and velocity, as well as time scales. Analogous to previous observations made with the normal alkane sprays, the behavior of the multi-component fuels correlate well with their bulk critical properties.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5065