ILASS - AMERICAS 2010 CONFERENCE PAPERS
TITLE: Large Eddy Simulations of Temporal Mixing Layers and Supercritical Thermodynamic Conditions: O2/H2
ABSTRACT: Please see full paper for abstract: ILASS2010-179.PDF
AUTHORS: Ezzi S. Taskinoglu, California Institute of Technology
Josette Bellan, Jet Propulsion Laboratory, California Institute of Technology
TITLE: High-speed Shadowgraphy investigation on a flashing liquid jet
ABSTRACT: Flash-atomization occurs when a liquid fuel is injected into a chamber where the ambient pressure p∞ is lower than the fuel saturation pressure psat(Tinj) The inception of flashing strongly depends on the level of superheat (Rp=psat(Tinj)/p∞) and on the transient heat conduction process within the jet. If flashing occurs, then jet disintegration is induced by bubble bursting. This process has a strong impact on the spray morphology and droplet size distribution, and hence on the combustion efficiency of the engine.
The study of a flash-disintegrating jet is particularly relevant for the aerospace industry. When expanding high-pressure fluids into near vaccum, e.g. during engine start-up , a state of high superheat may be attained and the process of mixture formation occurs through flash atomization and vaporization. Despite its technical relevance, a comprehensive and verified model for superheated jet disintegration is still not available due to the paucity of reliable experimental data.
The present study aims at providing a comprehensive database for model validation, which includes data on spray morphology, droplet size, velocity and temperature distributions. As first step, a new test bench was designed for performing flash atomization experiments at low pressure and near vacuum conditions. This paper analyses the transient behavior of a flash-atomizing jet, investigated by means of high-speed shadowgraphy.
The experiments are carried out with ethanol and acetone issuing from a small nozzle into a vacuum chamber. The chamber is equipped with a fast-response, heated injector. The experiments are performed at ambient temperature and chamber pressure p∞ varying between 0.02 and 0.4 bar. The injection pressure is fixed to 10 bar and the injection temperature Tinj varies between 30 and 170C.
The high-speed photographs enabled the visual inspection of the flashing jet structure and geometry. For low superheat conditions, no difference was obs
AUTHORS: Hend Kamoun, Institut fr Thermodynamik der Luft- und Raumfahrt (Institute of Aerospace Thermodynamics), Universitt Stuttgart, Germany
Grazia Lamanna, Bernhard Weigand Institut fr Thermodynamik der Luft- und Raumfahrt (Institute of Aerospace Thermodynamics), Universitt Stuttgart, Germany
Johan Steelant ESTEC-ESA, Noordwijk, The Netherlands
TITLE: Direct Injection Multi-hole Spray and Mixing Characterization of Ethanol Gasoline Blends in Engine
ABSTRACT: Multi-hole gasoline injectors are being adopted as the direct injection (DI) fuel injector of choice as vehicle manufacturers look for ways to reduce fuel consumption without sacrificing power. To realize the full benefits of direct injection, the resulting spray needs to be well atomized with appropriate fuel vapor concentration near the spark plug. Ethanol and its gasoline blends synergistically improve the DI gasoline performance especially in down-sized engine, with the aid of variable valve train. This paper presents the spray imaging results of a multi-hole gasoline injector with fuels ranging from E0 to E100 and environmental conditions that represent engine operating points under variable intake valve timing. Both high-speed Schleiren and Laser Mie results are shown inside pressurized chamber and optical accessible engine. Validations of multi-dimensional Computation Fluid Dynamics (CFD) model for predicting spray behaviors inside the chamber and engines are also discussed.
AUTHORS: Atsushi Matsumoto
Xingbin Xie, Yi, Zheng, Ming-Chia Lai, Wayne State University; Wayne Moore, Delphi Corporation
TITLE: Fine Spray Behaviour upon Impaction of Varied Material Surfaces
ABSTRACT: A mobile fine spray unit, utilising a spill return atomiser has been developed for the purpose of decontamination within healthcare environments. The unit must be able to spray uniformly onto any given surface, providing mist like coverage. Any streaking patterns on the surface during or after spray application would jeopardise the efficiency of delivering the decontaminant. Thus it is pertinent to understand the behaviour of droplets impacting on various surfaces, and particularly the conditions that cause streaking.
Within this investigation four sample surfaces; steel, acrylic, glass and laminated wood have been sprayed separately using the spill return device with a substitute MRSA disinfectant liquid. Through experimentation the optimum spray input conditions for the atomiser: distance, time and pressure required to uniformly coat various surfaces without the occurrence of streaking have been obtained.
AUTHORS: J.A. Stewart, University of Salford
G.G. Nasr and M. Burby, University of Salford
TITLE: A Computational Study of Viscoelastic Droplet Collisions
ABSTRACT: A computational study of oblique binary viscoelastic droplet collisions is performed. The free surface is modeled by a Lagrangian moving-mesh interface tracking method which is validated against analytical solutions and experimental data for binary Newtonian droplet collisions. Mesh quality is consistently maintained using a topological adaptation algorithm along with mesh smoothing. This method was then applied to the collision of viscoelastic droplets through a finite volume implementation of the linearized Phan-Thien-Tanner constitutive stress equation. The extensional nature of an oblique droplet collision highlights the transient effects of the large Trouton ratios typically found in this class of fluids though increased stabilization of fluid ligament structures. By altering the spray kinematics in this manner, the spray characteristics as a whole are changed by the viscoelastic rheological effects. The fully three dimensional computational study investigated the effect of Weber number, Deborah number and impact parameter on droplet collision.
AUTHORS: Kyle Mooney University of Massachusetts Amherst
Sandeep Menon, David P. Schmidt, University of Massachusetts
TITLE: Empirical and theoretical analysis of the stability of an air-assisted atomising annular liquid sheet
ABSTRACT: A novel application of a correlation-based measurement technique combined with high speed magnified imaging is employed to measure the interfacial stability properties of an air-assisted atomising annular liquid sheet in the near-nozzle region prior to sheet break-up. Comparison between theoretical stability analysis and such empirical data for the atomisation of liquid sheets has been extremely limited due to the challenging complexities of undertaking measurements in the near-nozzle region where the instabilities amplitudes are extremely small. Using this new technique, extraction of the spatial wave numbers (frequencies), wave speeds and spatial growth rates of the initial instabilities can be extracted with sufficient precision and accuracy to permit a comparison with stability analysis models. Variations in the stability properties are investigated against variation in the liquid and air-assisted co-flow momentum. It is further demonstrated that within the region of approximately one sheet thickness from the nozzle exit, the growth of the initial instability is approximately linear. A whole volume-of-fluid linear stability
analysis, solving the Orr-Sommerfeld equations, is thus undertaken in order to permit comparison with empirical data in the near-nozzle region. Some improved agreement between empirical and theoretical analysis is observed, permitting a more rigorous analysis of the use of stability analysis as an analytic tool for sprays.
AUTHORS: Daniel Duke, Laboratory for Turbulence Research in Aerospace and Combustion, Monash University
Damon Honnery and Julio Soria, Laboratory for Turbulence Research in Aerospace and Combustion, Monash University
TITLE: Spray patternation of a multi-hole injector utilizing planar line-of-sight extinction tomography
ABSTRACT: Spray characteristics of a multi-hole injector intended for use in direct-injection gasoline engines have been eva-luated for a variety of operating conditions including those that promote flash boiling. Planar line-of-sight extinc¬tion tomography was employed to evaluate spray patterns to determine the influence of ambient pressure and tem¬perature and fuel pressure and temperature on spray structure. Under severe flash boiling conditions, sprays were found to collapse and change shape significantly
AUTHORS: Scott E. Parrish, General Motors R&D
R. J. Zink General Motors R&D 30500 Mound Road Warren, MI 48090-9055 USA, Y. Sivathanu and J. Lim En’Urga Inc. 1291A Cumberland Ave. West Lafayette, IN 47906
TITLE: Spray Diagnostics at the Advanced Photon Source 7-BM Beamline
ABSTRACT: In recent years, x-ray radiography has been used to probe the internal structure of dense sprays. Quantitative measurements of spray mass distribution have been obtained on microsecond time scales and with spatial resolution of 15 m even in high-pressure environments. These data have been difficult or impossible to obtain with conventional optical diagnostics. A limitation to these measurements is the need to perform them at a synchrotron light source. While several synchrotrons are available throughout the world, the experimental time at these facilities is competitively awarded and is often limited. This has limited the scope of previous spray radiography measurements.
Recently, the US Department of Energy has funded the construction of an experimental station largely dedicated to x-ray spray measurements at the Advanced Photon Source. This facility provides significantly enhanced access to the x-ray beam in an environment tailored to spray measurements. The spatial resolution and x-ray intensity at this beamline also represent a significant improvement over previous x-ray radiography measurements. The capabilities of the beamline will be outlined in detail. Sample data from a diesel spray from a 110 m single-hole nozzle will be used to demonstrate the capabilities of the new beamline for performing spray measurements. The future prospects for additional measurements of sprays and spray systems will also be discussed.
AUTHORS: Alan L. Kastengren, Argonne National Laboratory
Christopher F. Powell, Eric Dufresne, Dohn Arms, and Jin Wang, Argonne National Laboratory
TITLE: Effect of Grid Spacing in Large-Eddy Simulation of Evaporating Drops in a Mixing Layer
ABSTRACT: Please see full paper for abstract: ILASS2010-178.PDF
AUTHORS: Senthilkumaran Radhakrishnan, Jet Propulsion Laboratory, California Institute of Technology
Josette Bellan, Jet Propulsion Laboratory, California Institute of Technology
TITLE: Axial Development of Diesel Sprays at Varying Ambient Density
ABSTRACT: Due to their importance in the performance and emissions of diesel engines, diesel sprays are the subject of significant research interest. One of the most fundamental findings of this research has been that the width of sprays is strongly dependent on the density of the ambient gas environment. There is disagreement in the literature, however, concerning the quantitative relationship between spray width and ambient density. A limitation in these previous studies is the use of optical diagnostics, which focus on the periphery of the spray.
X-ray radiography is a well-established technique to probe the internal structure of transient diesel sprays. Unlike optical techniques, it can provide quantitative data regarding the mass distribution of dense sprays. Previous x-ray radiography work examining the relationship between ambient density and spray width showed that, similar to variable-density gas jets, a rescaling of the spray axial coordinate to account for the density ratio between the jet and ambient fluids can account for much of the variation in spray width with ambient density. A limitation of this previous work was the limited field of view available for the x-ray radiography measurements, particularly for the low ambient density cases. Moreover, this previous work largely focused on the steady-state spray behavior.
The current work will examine the influence of ambient density on diesel spray structure over an expanded range. A smaller nozzle and larger windows will be used compared to previous x-ray radiography work, allowing more firm conclusions regarding the applicability of axial rescaling to account for ambient density effects. The influence of ambient density on the structure of the spray leading edge will be discussed as well as the steady-state spray behavior.
AUTHORS: Alan Kastengren, Argonne National Laboratory
Christopher F. Powell, Zunping Liu, Seoksu Moon, Jian Gao, and Jin Wang, Argonne National Laboratory
TITLE: Simulating Electrohydrodynamic Atomization for Fuel Injection
ABSTRACT: Over the past decade, there has been considerable interest in controlling the emissions from small engines in the size range of 200 cubic centimeters or smaller. Fuel injection schemes may reduce the incidence of pollutant emissions. However, the cost of implementation is a barrier to large scale adoption.
One approach to small-scale fuel injection is to capitalize upon the benefits of electrohydrodynamics (EHD) and enhance fuel atomization. There are many possible benefits to EHD aided atomization for combustion, such as smaller droplets, wider spray cone, and the ability to control or ``tune" the spray for improved performance. The objective of this work is to employ recently advanced, state-of-the-art numerical schemes to conduct direct numerical simulation (DNS) of electrohydrodynamic atomization.
Numerical simulations employs the recently-developed
adaptive spectrally refined interface (ASRI) tracking method coupled to a robust and accurate Navier-Stokes/Ghost fluid
solver. The NGA code, a high-order fully conservative finite difference scheme, is used for high-fidelity simulations. The ASRI interface tracking methodology provides several features that improves the accuracy and
resolution of the liquid structures. A novel numerical scheme for EHD has been developed using a sharp and robust implementation of the ghost fluid method (GFM). The combination of these numerical tools permits full DNS of electrostatic-aided liquid atomization. This research explores primary atomization for high electric Reynolds number EHD, whereby volumetric space charge influences the liquid breakup.
Electrohydrodynamic flows and sprays have drawn increasing interest in recent years, yet key questions regarding the complex interactions among electrostatic charge, electric fields, and the dynamics of atomizing liquids remain unanswered. Two relevant research questions explored in this work include:
a. Role of electric Reynolds number. Does surface charge play
AUTHORS: Bret P. Van Poppel, University of Colorado at Boulder
Olivier Desjardins and John W. Daily, University of Colorado at Boulder
TITLE: A Prediction of Primary Atomization for a Subsonic Spray in Crossflow Using the Sigma-Y Model
ABSTRACT: The prediction of spray formation occurring when a liquid jet is injected normally to a high velocity gas stream is of fundamental interest to a variety of combustion and power related applications.Of primary interest is the penetration of this liquid jet and the characteric droplet diameter of the resulting spray.The sigma-Y model for primary atomization has proven successful in predicting a number of high-velocity diesel and coaxial type injection arrangements, but has yet to be tested in more complex flow configurations Evaluating the model’s generality in predicting arbitrary injection configuration is fundamental in gauging its potential as a practical engineering tool. Encouraging preliminary results presenting the models ability to predict mass distribution and spray penetration of sprays in cross flow are presented and compared to experimental PDPA measurements.
AUTHORS: Nathaniel Trask, University of Massachusetts
David P. Schmidt, University of Massachusetts
TITLE: Measurement of Thin Liquid Film Characteristics using Laser Focus Displacement Intruments for Atomization Applications
ABSTRACT: Dynamic thin liquid films are present in numerous engineering applications including atomizers, wave plate mist eliminators, and refrigerant flows in evaporators. As computational models emerge and evolve to describe the complex behavior of such films, experimentalists search for robust methods for validating these models. An experimental film thickness measurement technique is one example of the desired methods, and here a laser focus displacement instrument (LFD) is explored as a solution. An LFD utilizes the confocal principle with laser light to determine the location of an interface between two media. The device has seen use in static applications such as product quality verification processes where spatial accuracy is paramount, and a limited few research groups have applied an LFD to fluid dynamics applications such as would be encountered in atomization processes. Although researchers had success using the instrument as a film thickness measurement technique, there lacks a comprehensive study of the technologys capabilities when used as such. This study examines the abilities of the LFD technology by isolating and quantifying its limitations, including optical configuration as well as fluid properties such as refractive index. Following a detailed description of the instrument, theoretical calculations and static liquid experiments were performed to identify the maximum surface angle which allows measurement. This limitation is important for wavy liquid film applications. The surface angle limitation, combined with temporal resolution, will largely determine whether a time-resolved film surface profile can be obtained or if only time-averaged film thickness measurements are possible. An LFD was applied to both gravity driven films and shear-driven films to show the significance of film surface dynamics and experimental thickness measurements are presented for both cases. The experimental results and analysis show that the specific model of LFD utilized in th
AUTHORS: Jeffrey Wegener, University of California-Los Angeles
James Drallmeier, Missouri University of Science and Technology
TITLE: Stochastic Spray Flow Models: A Review
ABSTRACT: Understanding and modeling multiphase flows is of primary interest in a wide variety of applications. Most theoretical and numerical models of multiphase flows can be placed into one of three categories: Eulerian-Eulerian, Lagrangian-Eulerian, or stochastic methods. With the Eulerian-Eulerian approach, a set of conservation equations is written for each phase, and the sets are coupled through their respective source terms. Typically, the spatial resolution of the Eulerian-Eulerian formulations is much larger than the interparticle spacing, and thus the discrete phase is treated as through it were a continuous medium with its own material properties. In the Lagrangian-Eulerian particle tracking framework, drops are injected into the gas and the drop trajectories are computed by numerically integrating Lagrangian equations of motion. Because of the large number of drops in a typical spray, computational parcels are often employed, where each parcel represents some number of individual drops. Probabilistic, or stochastic, methods generally involve the development of a probability density function (pdf) describing the random variables representing droplet properties, and computing the evolution of that pdf as the drops move through the gas phase, undergo secondary breakup, heat, and vaporize. This approach allows one to calculate general and/or detailed statistics about the spray drops and the gas phase at each point in the flow. This paper presents a survey of stochastic spray modeling frameworks that have appeared in the literature. A review of the spray equation and the sectional approach provides a background to a more extensive discussion on specific modeling methods including assumed pdfs, maximum entropy moment closure, and particle methods. The assumed-pdf method is the simplest to implement but has the disadvantage that there is no guarantee the spray characteristics will always conform to the assumed form. The assumed forms may be anything from a de
AUTHORS: Mark R. Archambault, Florida Institute of Technology
TITLE: A KIVA-based Model for Liquid Jet in Cross Flow
ABSTRACT: KIVA-III code was employed to model the atomization of a liquid Jet In Cross Flow (JICF). The liquid jet was represented by injecting single droplets into cross flow continuously and they were forced to follow the jet trajectory associated with an experimental correlation. Furthermore, these droplets were not allowed to go through aerodynamic breakup and collision. This takes account of wake region behind the jet, which might be important in secondary breakup of the droplets. In the present study, in order to model the droplet shedding along the liquid jet at high gas Weber number (i.e. shear breakup regime), a number of nozzles were located on both sides of the jet between the locations of the onset of the droplet shedding and the column breakup. The properties of theses nozzles including number, stripping mass rate, size and velocity of the droplets were obtained from phenomenological sub-models and experimental correlations. The results consisting of droplets size, velocity and volume flux distributions were compared with those of available experiments in a similar flow conditions. The model was able to capture the trend which existed in the experiments and there was a fare agreement between the droplets size and volume flux obtained by the model and the experimental results.
AUTHORS: Mohsen Behzad, Graduate Research Assistant, Dept. of Civil Eng., University of Toronto
Alireza Mashayek, Graduate Research Assistant, Dept. of Physics, University of Toronto and Nasser Ashgriz, Professor, Dept. of Mechanical and Industrial Eng., University of Toronto
TITLE: Exploration of Near-Field Structures of Aerated-Liquid Jets in a Quiescent Environment Using the X-Ray Technique
ABSTRACT: The structures of pure- and aerated-liquid jets injected into a quiescent environment have been explored, using the phase contrast imaging technique combined with the x-ray light source, available at the Argonne National Laboratory. Never-before-seen features on the liquid column surface of the pure-liquid jets were observed and qualitatively described in the previous study. The x-ray phase contrast imaging can also provide the unique capability of depicting interfacial features on the entire periphery of the liquid column, ligament, and droplets. The near-field structures of aerated-liquid jets, which are optically dense, can be clearly depicted by the present diagnostic technique.
With these promising findings, more data were recently obtained from the same test facility. The specific objectives of this experiment are to explore the near-field structures of pure- and aerated-liquid jets and the two-phase mixtures within the aerated-liquid injectors and to quantitatively characterize the structure of aerated-liquid jets in terms of droplet size and number density. Water is the test injectant and nitrogen is the aerating gas. Two previously-designed aerated-liquid injectors were utilized for the experiment for the exploration of near-field structures of the aerated-liquid jets. In addition, two 2-D injectors equipped with diamond windows were designed and fabricated. The diamond windows provide x-ray access into the mixing chamber at various locations for the exploration of internal two-phase mixtures. A total of 5 window locations was selected, ranging from the first row of the aerating tube to near the injector exit. The evolution of the internal two-phase mixture was, therefore, thoroughly investigated. The near-field spray structures generated from the specifically-contoured cavitators was also evaluated.
An effort to quantitatively measure the droplet size from the images taken from the x-ray phase contrast imaging was initiated during this research peri
AUTHORS: Kuo-Cheng Lin, Taitech, Inc.
Christopher Rajnicek, Campbell Carter, Air Force Research Laboratory, Kamel Fezzaa, Argonne National Laboratory
TITLE: Droplet Nucleation Processes Inside the Injectors of Supercritical Ethylene Jets
ABSTRACT: The structures of condensed supercritical ethylene jets inside a rectangular injector were explored, using the small-angle x-ray scattering (SAXS) technique. The experiment was conducted at the 8-ID beamline at the Argonne National Laboratory. The rectangular injector is equipped with diamond windows at various axial locations for x-ray access. Scattering intensity as well as size and population of droplets were measured and calculated. Evolution of the internal flow properties, along with the effects of injection temperature and injector internal geometries on nucleation/growth processes, were investigated.
The ability of the SAXS technique to measure tiny incipient droplets generated from the homogeneous nucleation process is demonstrated in the present study. The measured incipient droplet size is in the range of 30-100 (3-10 nm). The present efforts also demonstrate, for the first time, the capability to explore a highly dynamic supercritical ethylene jet inside an injector. Populations of x-ray scatterors of two sizes were observed inside the injector. One population is on the order of 100 and is consistently present inside the injector. The other population is on the order of 1000 and is mainly present in the downstream region. These 1000 droplets, however, are strongly associated with window assembly issues realized during the experiment and post-test analysis. The present study observes more large droplets along the injector wall.
It was also found that the injection condition with an injectant temperature close to the critical temperature promotes early occurrence of the nucleation process, which allows a longer residence time for nuclei to grow with more readily available ethylene molecules into large droplets. Evidence that the nucleation/growth processes also depend on the injector contour are obtained in the present study. In particular, the converging angle leading to the final nozzle passage affects the expansion process of the injected flu
AUTHORS: Kuo-Cheng Lin, Taitech, Inc.
Campbell Carter, Air Force Research Laboratory, Alec Sandy, Suresh Narayanan, Jan Ilavsky, Jin Wang, Argonne National Laboratory
TITLE: Three-Dimensional Penetration and Velocity Distribution of Liquid Jets Injected Transversely into a Swirling Crossflow
ABSTRACT: An experimental study has been conducted to study the effect of a swirling crossflow on transversely injected liquid jets. In-house designed axial swirlers, with vane exit angles of 30, 45 and 60, were used to generate a swirling crossflow and the resulting flowfield was investigated using Laser Doppler Velocimetry (LDV). The resultant flow was close to a solid body rotation with the flow angle lesser than the swirler vane exit angle. The deficit in the flow angle increased with an increase in the swirl angle. Multi-plane Particle Image Velocimetry (PIV) studies were conducted in order to study the jet penetration and the progress of the spray plume in the 3-D flowfield. PIV measurements were conducted in streamwise planes (reported previously) and cross-sectional planes. The Mie-Scattering images from the measured planes were collated to form a 3-D representation of the spray plume. The jets were observed to follow a curved (helical) trajectory. As a result, it was found to be more beneficial to conduct the penetration analysis in a cylindrical frame of reference. The angle made by the jet trajectory trailed the flow angle of the crossflow due to a phenomenon described here as a circumferential penetration, which describes the opposition to circumferential (tangential) displacement of the jet caused by the tangential momentum of the crossflow. The radial penetration of the jets was observed to be higher than that of an equivalent jet in a uniform crossflow. Increasing the momentum flux ratio (q) increased the radial penetration while increasing Weber number (We) had no effect on the penetration. As the swirl angle of the crossflow increased, the radial penetration decreased while the circumferential penetration as well as the tangential displacement of the jets increased. The PIV results from the cross-sectional and streamwise planes were combined to obtain the 3-D velocities of the droplets throughout the spray plume. As the jets move downstream, the droplet veloc
AUTHORS: Samir B. Tambe, University of Cincinnati
San-Mou Jeng, University of Cincinnati
TITLE: Time-Resolved Measurements of In-Cylinder Fuel Spray and Combustion Characteristics using High-Speed Flow Visualization and Ionization Sensing
ABSTRACT: A time-resolved measurement technique combining the diagnostic tools of high speed flow visualization and high frequency in-cylinder ionization sensing was implemented to evaluate the fuel air mixture formation and combustion characteristics in a single cylinder engine with optical access to the combustion chamber. In-cylinder spray and combustion images were taken at an acquisition rate of 10,000 frames per second with simultaneous recordings of both in-cylinder ionization and pressure signal traces within a complete engine cycle. The results reveal that, prior to the combustion event, the injector spray pattern and injection timings affect the fuel-air mixture formation, spray impingement on cylinder wall, and fuel distribution near the spark plug in the cylinder. After combustion is initiated, the synchronized combustion images with in-cylinder ionization measurements provide more cycle-resolved information about the combustion characteristics, from the onset of spark ignition to flame propagation and to flame quenching at the cylinder wall. Combining and synchronizing the high speed images with in-cylinder combustion ionization and pressure signals improve the understanding of fuel mixture distribution, combustion characteristics, flame propagation, and the quality of combustion in the engine combustion chamber.
AUTHORS: David L.S. Hung, Michigan State University
George G. Zhu and Harold Schock, Michigan State University
TITLE: A VAPORIZATION MODEL FOR REALISTIC MULTI-COMPONENT FUEL SPRAYS
ABSTRACT: A vaporization model for multi-component fuel sprays is described. A new approach, named the discrete/continuous multi-component (DCMC) model, was used to model the properties and composition of gasoline fuel. In this approach gasoline is composed of five discrete families of hydrocarbons: n-paraffins, i-paraffins, naphthenes, aromatics, and olefins. Each family of hydrocarbons is composed of an infinite number of continuous components, which are modeled as a probability density function (PDF), and the mass fraction of each family of hydrocarbons (PDF), and the mean and variance of each PDF is tracked. Compared with the discrete multi-component (DMC) model, which must model hundreds of components for gasoline, the DCMC model saves computer time. Compared with the continuous multi-component (CMC) model, the DCMC model has much higher accuracy. Unsteady vaporization of single and multi-component fuel droplets and sprays was considered for both normal and flash-boiling evaporation conditions. An unsteady internal heat flux model and a model for the determination of the droplet surface temperature were formulated. An approximate solution to the quasi-steady energy equation was used to derive an explicit expression for the heat flux from the surrounding gas to the droplet-gas interface, with inter-diffusion of fuel vapor and the surrounding gas taken into account. The present vaporization models were implemented into a multi-dimensional CFD code and applied to calculate evaporation processes of single and multi-component fuel droplets and sprays for various ambient temperatures and droplet temperatures. Differences between representing model fuels using the single and multi-component fuel descriptions are discussed.
AUTHORS: Shiyou Yang, University of Wisconsin-Madison
Youngchul Ra, and Rolf D. Reitz, University of Wisconsin-Madison
TITLE: Modeling Charge Preparation and Combustion in an Ethanol-Fueled PPCI Engine
ABSTRACT: Partially premixed compression ignition (PPCI) has been shown to be a promising strategy to simultaneously reduce NOx and soot emissions while realizing improved fuel economy. Many studies have explored the benefits of PPCI operation using high cetane fuels (e.g., diesel fuel); however, only recently have low cetane fuels been explored as viable future fuel for compression ignition operation. Recent research has shown promising results when low cetane fuels, such as gasoline and ethanol, are used in a PPCI engine. The reduced fuel reactivity of low cetane fuels increases the ignition delay and allows higher load PPCI operation. Additionally, since ethanol can be produced from a wide range of renewable sources, it is of interest to explore and characterize PPCI engine operation using ethanol and ethanol gasoline blends.
PPCI combustion uses high levels of pre-combustion mixing to avoid rich regions and lower soot levels. The high level of pre-combustion mixing results in a primarily kinetics controlled combustion process. Because reaction rates are very sensitive to temperature and equivalence ratio, modeling of PPCI combustion requires precise treatment of the injection, evaporation, and mixing processes. In this work multi-dimensional modeling is used to explore charge preparation and combustion of neat ethanol and blends of ethanol and gasoline in a direct-injection, compression-ignition (DICI) engine. Modeling is performed using the KIVA-CHEMKIN code with a Discrete Multicomponent (DMC) fuel vaporization model. Oxidation of gasoline is evaluated using a reduced primarily fuel reference (PRF) mechanism that has been extensively validated against experimental data. The PRF mechanism was extended to describe the decomposition of ethanol through the addition of 4 species and 33 reactions. In this work, the combined PRF-ethanol mechanism is validated against detailed mechanisms for primary reference fuels and ethanol.
Simulations are performed and
AUTHORS: Sage L. Kokjohn, University of Wisconsin-Madison
Jessica L. Brakora and Rolf D. Reitz, University of Wisconsin-Madison, Vittorio Manente and Bengt Johansson, Lund University
TITLE: The Effect of Flashing on Characteristics of Sprays of Splash-Plate Nozzles
ABSTRACT: An experimental study of flash evaporation of water in splash-plate nozzles was conducted. This type of nozzle is used in pulp and paper industry to inject black liquor in recovery boilers. If the temperature of the liquid is above the saturation temperature corresponding to the back pressure, sudden pressure drop in the liquid passing through the convergent part of the nozzle leads to abrupt bubble nucleation and bubble growth, the phenomenon which is referred to as flashing.
In splash plate nozzles a circular jet impinges on a plate and forms a sheet of liquid. In non-flashing condition, the jet breakup is due to sheet instability and growth of perforations in random locations on the sheet. The observations suggest that increasing the liquid temperature, by only a few degrees above the saturation temperature, initiates flashing and completely changes the breakup regime. Observations of the internal flow revealed that small number of bubbles appear inside the tube feeding the nozzle. Increasing the temperature to 4-7K above the flashing point leads to a spray that is not intact; small liquid sheet segments are observed which break and/or shrink to ligaments and droplets. Slug flow inside the nozzle tube in this temperature causes an oscillatory type of flow in the nozzle exit and hence separates the sheet into segments. Further increase in temperature completely shattered the liquid prior to impingement. The flow regime at this temperature is normally annular or wispy annular, which due to high velocity and mixing with vapor cannot form an intact liquid sheet. The initiation point of flashing is highly dependant on flow and delivery system characteristics. Increasing the injection pressure moves the nucleation point towards the nozzle orifice. At very high pressures, evaporation occurs after the nozzle exit. Increasing the temperature shifts the nucleation point upstream.
The flashing process also affects droplet size and velocity distributions. Increasing the
AUTHORS: Abdolreza Karami, Mechanical & Industrial Engineering Department, University of Toronto
Nasser Ashgriz, Mechanical & Industrial Engineering Department, University of Toronto, Honghi Tran, Chemical Engineering Department, University of Toronto
TITLE: Multicompartmental Microstructured Materials via Electrohydrodynamic co-jetting : a diagnostic and bio-sensing platform
ABSTRACT: Control over nano- and microscale architecture of polymeric materials is highly desirable for improved versatility, utility, and performance of biomedical devices, which include smart drug release systems, biomedical coatings, surgical dressings, and multiplexed bioassays. Apart from size and shape of polymeric micro-objects, phase distribution, or selective material compartmentalization has been shown to be increasingly important for maximizing device performance.1 We herein demonstrate the fabrication of multicompartmental microparticles and microfibers from biodegradable polymers via electrohydrodynamic co-jetting.2 In its simplest form, two polymer solutions are flown through a modified side-by-side capillary system. Application of an electric field results in the formation of an electrospray, and solvent evaporation results in particle formation. The interface between two polymer solutions is sustained during jet fragmentation and size reduction. Because of its intrinsic simplicity and generality, the electrohydrodynamic co-jetting process can be applied to a wide range of specialty and non-specialty materials. Furthermore, simple variations of different solution and process parameters, such as concentration, flow rate, applied voltage, etc. provides access to a vast repertoire of shapes and sizes of particles.4 Such novel particle geometries enable independent control of key parameters, such as chemical composition, surface functionalization, biological loading, shape, and size for each compartment. In this work, we demonstrate the fabrication of multicompartmental particles and fibers from biodegradable polylactide polymers via electrohydrodynamic co-jetting. We then demonstrate the versatility of this process by fabricating a variety of non-equilibrium biphasic shapes, such as discs and rods, in addition to spheres.4,5 Spatioselective control over particles surface is demonstrated via introduction of free acetylene groups in one hemisphere of biphasic microp
AUTHORS: Srijanani Bhaskar, University of Michigan Ann Arbor
Kelly Marie Pollock, Cornell University, Himabindu Nandivada, Xiaopei Deng, JOnathan Hitt and Joerg Lahann
TITLE: Droplet Lamella Lift Dynamics and Surface Wettability
ABSTRACT: Droplet impact on dry surfaces remains an issue for a variety of important applications such as fuel injection, spray cooling, metallurgy, pesticides and coatings. The mechanisms that initiate splashing are highly complex and differ from those on pre-wetted surfaces. In a recent work, the authors determined a timeline of events initiating splashing consisting of: lamella formation, lamella lifting, finger formation, and finger elongation and breakup. The momentum transfer from the surrounding gas phase into the spreading lamella was found to be critical to splash initiation. The droplets affinity for the impact surface was also believed to influence the threshold for lamella lifting. In this work, droplet wettability on a smooth, dry glass surface is examined further to quantitatively determine its influence on splashing. Hydrophobic and hydrophilic coatings were applied to the glass in order to change wetting characteristics. Water-glycerol mixtures from 0-50% were used to vary liquid viscosity and slow impact dynamics recorded using a high-speed video camera. Progressive, receding and static contact angles were measured to characterize the level of wetting. Highly volatile FC72 was also used to simulate a condition of zero wettability due to the vapor layer that forms on the surface during impact. It was found that higher wettability increases the required momentum transfer from the gas to the liquid droplet for splashing to occur. A splashing threshold correlation was modified to account for this effect. Heating impact surfaces at or near the liquid boiling temperature may also be a method to reduce wettability and may have important consequences for many applications.
AUTHORS: Henry Vu, University of California, Riverside
Guillermo Aguilar, University of California, Riverside
TITLE: Effect of Viscosities on the Instability of Sprays from a Swirl Atomizer
ABSTRACT: The phenomena of breakup of liquid sheets and jets are encountered in daily life as well as in various industrial applications. This paper studies the effects of liquid viscosity and surface tension on the spray instability during the transient operations of a swirl atomizer in a trigger sprayer via experimental investigations. In the experiments, water-glycerol mixtures were used to simulate different fluids with a wide range of viscosity variation as well as water-glycerolisopropanol mixtures were used to simulate different fluids with different surface tension. A high-speed digital camera was used for the near-nozzle spray structure visualization. The axisymmetric three-dimensional wave patterns can be clearly obtained in a conical liquid sheet produced by the swirl atomizer. The digital images of the sprays were further processed to analyze the spatial and temporal surface waves on the spray cone. From the experimental results, it is seen the fluid viscosity play very important role in controlling the liquid sheet breakup and atomization. The spray cone angle variations were calculated for various viscous fluids. It is found that more viscous fluid leads to a smaller average spray cone angle value. The spray cone developed vary fast during early stage, while for very viscous liquid, it turns that they have very small cone angle with little breakup. With the increase of viscosity, the cone collapse earlier with larger droplets in the end stage. The surface wave temporal frequency is also analyzed for different viscosity fluid. The results show that with the increase of fluid viscosity, the surface wave temporal frequency decreases. Compare with similar viscosity, spray structure of liquid sheet is more irregular for the liquid with various surface tensions. Surface tension suppresses the breakup of spray with high viscosity and the air core cannot form near the end of spray.
AUTHORS: Shanshan Yao
Ji Zhang, Tiegang Fang, North Carolina State University
TITLE: Temporal analysis of instabilities in the column of a plain liquid jet in a crossflow using image processing
ABSTRACT: The injection of a plain liquid jet into a gaseous crossflow has been studied extensively in the past decades. Numerous empirical models describing the aspects of the breakup, penetration and dispersion of the liquid jet have been developed based on the experimental data. In recent years, however, the developments of detailed models for the behavior of the jet evolve and more quantitative model for the jet breakup process are receiving more interest due to the progress of CFD modeling of liquid jet. Furthermore, as more sophisticated simulation approaches such as surface tracking methods evolve, a richer database for assessing accuracy is of great interest. The present work extends work done to assess column breakpoint and trajectory of plain liquid jets using analysis of high resolution, high speed digital imaging. In particular, temporal liquid column characteristics such as instability frequencies are assessed in the present work.
AUTHORS: Qing Wang Energy Research Consultants
Christopher Brown, Vincent McDonell, Energy Research Consultants
TITLE: Effect of injection pressures on GDI spray and atomization of different fuels
ABSTRACT: Liquid fuel atomization is critical to the combustion and emissions in gasoline engines. Meanwhile, renewable alternative fuels, such as bio-butanol and bio-ethanol, have received much attention due to the elevated fossil fuel depletion. These biofuels have quite different chemical and physical properties, and the property variation among different fuels can greatly affect the spray and combustion characteristics. In this paper, the effect of injection pressures on the liquid spray formed by a Fuel Stratified Injection (FSI) injector with different fuels, including butanol, ethanol, Exxon-mobile gasoline, and Shell gasoline, was investigated. The injection pulse width was calibrated for each fuel at different injection pressures to ensure the same fuel quantity per injection for all the conditions. A high speed camera was used to capture the images of the spray, which was volumetrically illuminated. Droplet size distributions of the sprays were analyzed by using a laser diffraction technique with a commercial Malvern SprayTec particle analyzer at a sampling rate of 10 kHz. From the experimental results, it is seen that the injection pressure plays an important role in determining the spray structure, its development, and the liquid fuel atomization. Under lower pressure, atomization of butanol was seen worse than that of gasoline and ethanol, while under higher pressures not much difference among fuels was observed. The early stage of the spray features some large droplets despite of the pressures and fuels. The spray cone is formed rapidly after the injection starts and the wave propagation on the cone surface can be observed. In the developed stage, higher pressure produces better atomization for all fuels, while the cone angle does not change much. During the ending stage, the spray is shut off very quickly with no large droplets observed out of the nozzle. The droplet size distributions further explain and confirm the observation in the images of the spray forma
AUTHORS: Ji Zhang
Shanshan Yao, Himesh Patel, Tiegang Fang, North Carolina State University
TITLE: Reduced Order Modeling of Steady and Unsteady Flow over a Sphere
ABSTRACT: Reduced order modeling is the process of generating low-dimensional models for infinite dimensional systems. A common application of reduced order modeling is to fluid flow. A fluid flow has an infinite range of flow states that can exist. However, in a typical fluids problem only a small range of those flow states is exhibited. To take advantage of this fact a tool like the proper orthogonal decomposition can be used. The proper orthogonal decomposition finds the smallest set of orthogonal functions (or POD modes) that can accurately represent the range of flow states. The governing equations for the flow can then be compressed onto the space of states described by those functions using weighted integral methods. This then results in a low dimensional model. In this talk we investigate the performance of such reduced order models for modeling unsteady flows over spheres. The accuracy of such models at both low and high Reynolds number and low and high Strouhal numbers is compared to classical models.
AUTHORS: Brian T. Helenbrook, Clarkson University
David Whitman, Clarkson University
TITLE: Pressure Swirl Atomization of Water-in-Oil Emulsions
ABSTRACT: The injection of water-in-oil emulsions is investigated experimentally for stabilized emulsions for a spray into an ambient environment. Stabilized water and diesel fuel #2 are well mixed with cor-responding surface stabilizing agents (surfactants) prior to emulsion formation. The stabilized components are flowed through a controlled shear device to generate size distributions with estab-lished droplet statistics. Two pressure swirl atomizers are used in the study (one with 20x the ca-pacity of the second). Laser diffraction is utilized to measure spray drop size statistics. Spray properties are investigated utilizing high speed cinematography and a mechanical spray patterna-tor. Results show that atomizer scale affects how the different emulsions behave. Analysis is pre-sented which illustrates the important factors that determine the spray characteristics for both ato-mizers.
AUTHORS: Christopher Bolszo University of California, Irvine
Adrian Narvaez, Vincent McDonell, Derek Dunn-Rankin, William Sirignano
TITLE: Evaporation rate and spread area of adjuvant-amended droplets on waxy and hairy leaves
ABSTRACT: The fate of pesticide droplets on leaves is seriously influenced by spray formulations and fine structures on leaf surfaces. Evaporation times and spread areas of droplets on hairy and waxy geranium leaf surfaces were determined under controlled conditions. For each treatment a single droplet was produced with a microprocessor-based timed mode, air-powered fluid dispenser. Droplet evaporation processes were taken with stereoscopic sequential images for various droplet sizes, relative humidity (RH) conditions and spray formulations. The spray formulations were combinations of water, a drift retardant, a surfactant, a fungicide and three insecticides. The evaporation time and spread area of droplets were significantly changed by adding the surfactant or drift retardant to the sprays, but not by adding the fungicide or insecticide. Droplet evaporation times on waxy leaves were longer than those on hairy leaves. Evaporation times increased exponentially as droplet diameter and RH increased with limited variability of regression coefficients independent of spray type and leaf surface. The spread area of droplets also increased exponentially as droplet diameter increased but it was not significantly affected by RH. On waxy geranium leaf surfaces, the spread area of pesticide droplets decreased throughout the evaporating process and at all RH conditions, while, on hairy leaf surfaces for the same droplets and at the same RH conditions, the contact area continued to spread until evaporation was nearly completed. Given that the duration of evaporation time and the extent of the spread area affect pesticide distribution on waxy or hairy leaves, recommendations for pesticide dosage and spray methods should be specifically customized for different plant species to obtain the optimal biological effect and reduced pesticide use.
AUTHORS: Heping Zhu, USDA/ARS Application Technology Research Unit, Wooster, Ohio, USA
Linyu Xu, Yang Yu, Erdal Ozkan
TITLE: Effects of Interfacial and Viscous Properties of Liquids on Drop Spread Dynamics
ABSTRACT: An experimental study of the post-impact spreading of liquid droplets on dry horizontal substrates is presented in this paper. The drop spreading and recoil behavior are captured using a high-speed digital video camera at 4000 frames per second. To ascertain the effects of liquid interfacial and viscous properties, experiments were conducted with five liquids (water, ethanol, propylene glycol, glycerin, and acetic anhydride). A range of drop Weber number from 20 to 120 was considered by altering the height from which the drop is released. Effects of liquid properties on droplet impact dynamics were determined by comparing liquids with different surface tension but similar viscosity and vice versa. The high-speed photographs of impact, spreading and recoil are shown and the temporal variations of dimensionless drop spread, height, and the dynamic variation of the contact angle are provided in the paper. Results show that changes in liquid viscosity and surface tension significantly affect the spreading and recoil behavior. For a fixed Weber number, lower surface tension promotes greater spreading and higher viscosity dampens recoil. A detailed comparison of maximum spreads observed in the experiments with those obtained using spread correlations available in the literature show significant differences. Limitations of the available correlations are discussed in the paper.
AUTHORS: Vishaul Ravi, University of Cincinnati
Milind A. Jog and Raj M. Manglik, University of Cincinnati
TITLE: Droplet-ambient sub-grid interaction modeling in large eddy simulation of diesel sprays
ABSTRACT: This work presents a large eddy simulation (LES) study of diesel sprays and particle laden flows. A one-equation dynamic structure LES model is used which solves an additional transport equation for sub-grid kinetic energy (k). The atomized liquid droplets are generally smaller than the computational cell, and therefore the sub-grid scale interaction of droplets with the ambient gas phase needs to be modeled in the LES of diesel sprays. This two-phase interaction is accounted through the spray source term in the k - transport equation. The spray source term is a dot product of the droplet drag and the gas phase sub-grid gas velocity. An approximate deconvolution technique is used to obtain the sub-grid velocities from the resolved flow field. The results of LES predicted mean and turbulence velocities for a particle laden jet are shown to compare very well with the previous experiments. A discussion on the sub-grid, resolved, turbulence and mean kinetic energies is presented. The non-evaporating diesel spray LES results are compared with previously published X-ray radiography experiments conducted at Argonne National Laboratory. The comparisons are made for quantities such as transverse integrated mass (TIM), mass averaged axial velocity profile and spray momentum. In diesel sprays, the near nozzle contribution from droplets to gas phase sub-grid kinetic energy is found to dominate the production and dissipation rates. The spray source term in evaporating sprays is found to have a significant effect on the spray evaporation and penetration characteristics.
AUTHORS: Nidheesh Bharadwaj, Engine Research Center, University of Wisconsin-Madison, USA
Christopher J. Rutland, Engine Research Center, University of Wisconsin-Madison, USA
TITLE: Breakup of Water-in-Oil Emulsions in Liquid Jets and Conical Sheets
ABSTRACT: The breakup process is investigated experimentally for water/oil emulsions. The effects of the dis-persed liquid phase and stabilizing an emulsion on breakup behavior is studied at ambient condi-tions. The results are utilized to explain the breakup process in pressure atomization experiments at fuel flow conditions typical in large-scale gas turbine applications. Stabilized water and diesel fuel #2 are well mixed with corresponding surface stabilizing agents (surfactants) prior to emulsion formation. Stabilized components are flowed through a controlled shear device to generate size distributions with established droplet statistics. The presence of the discrete phase in volume fractions below 0.5 are studied, which constitutes a mild non-Newtonian fluid behavior. To better understand the initial breakup of these types of emulsions, a simplified experiment utilizing a mono-dispersed droplet generator is used to isolate the ligament formation and droplet formation in an emulsion stream. The shear forces in these scenarios are used to relate the performance with the addition of shearing from pressure atomization. Laser diffraction is utilized to measure spray drop size statistics for these fuel emulsions. A novel dual-laser fluorescence method is evaluated to gain insight on the shear behavior in the current spray configuration by identifying the concentrated regions of oil and water
AUTHORS: Christopher Bolszo University of California, Irvine
Mina Rohani, Adrian Narvaez, Vincent McDonell, Derek Dunn-Rankin, William Sirignano
TITLE: A Numerical Method for Variable Surface Tension Effects in Non-Isothermal Atomization with Overset Grids
ABSTRACT: Overset or overlapping grids have been used to simulate a wide variety of flows. A typical overset grid consists of at least 2 curvilinear grids which cover a domain and overlap where they intersect. Flow field variables are transferred between the grids in the overlap region via appropriate interpolation functions. Overset grids can thus vastly simplify the grid generation process for complex 3-D geometries and flows with moving boundaries. They also lend themselves to problems requiring very high resolution in a region of the domain. Here we aim to couple an overset-grid method to our flow solver and interface tracking scheme for the purpose of high resolution atomization simulations.
The atomization process of turbulent liquid jets is as of this day not well understood. Detailed numerical simulations can help study the fundamental mechanisms in regions, where experimental access and analysis is virtually impossible. However, simulating atomization accurately is a huge numerical challenge since time and length scales vary over several orders of magnitude, the phase interface is a material discontinuity, and surface tension forces are singular. The Refined Level Set Grid (RLSG) method presented here, coupled to an overset meshing scheme, is one numerical approach to simulate the primary breakup process of liquid jets and sheets in detail.
With it, the liquid/gas phase interface is tracked by a level set method using an auxiliary high resolution equidistant Cartesian grid. This not only allows for application of higher-order WENO schemes retaining their full order of accuracy both for advecting and reinitializing the level set scalar, but it also provides the necessary high resolution of the phase interface geometry during topology change events in an efficient manner.
In many technical applications of interest atomization occurs in non-isothermal environments, like for example in combustion devices. In these devices, thermal fluctuations can be signific
AUTHORS: P. Brady, Arizona State University
M. Herrmann and J. Lopez, Arizona State University
TITLE: Ultra-Fast Phase-Contrast X-ray Imaging of Near-Nozzle Velocity Field of High-Speed Diesel Fuel Sprays
ABSTRACT: High-pressure, high-speed diesel fuel sprays are complex multiphase flow phenomena. Great ef-forts have been devoted to understand their dynamics that is essential to the breakup, especially, in this near-nozzle region. In the near nozzle region, conventional optical techniques are not effective to probe the velocity field in this optically dense region. By taking advantage of high-intensity and high-brilliance x-ray beams available at the Advanced Photon Source (APS), the morphology of the sprays can be imaged with x-ray phase contrast imaging and with sub-ns temporal resolution, Furthermore, a special x-ray timing mode was developed at the APS, so that two x-ray pulses with a few nanosecond width and a fixed interval of about 200 ns can be used to visualize the high-speed sprays. By tracking the movement of features in the double-exposure images without the need of seed particles, we have been able to extract velocity fields of the sprays. Velocity field is obtained by using local autocorrelation analysis of the double-exposure images of the entire sprays and during entire injection events.
In the experiment, two slightly different single-hole minisac nozzles were used, one with a hydro-ground rounded orifice inlet and the other one with a sharp inlet. In the quasi-steady state of the injection to 0.1 MPa nitrogen gas, the diesel sprays from the types of nozzles show distinct dy-namic behaviors near nozzle exit, showing different velocity fields. The velocity fields of the sprays from both nozzles are compared at the same distance from nozzle exit. The direct spray ve-locity mapping paves a way for understanding the dependence of discharge coefficients on nozzle geometry. The velocity field mapping also reveals the near-nozzle spray dynamics dependence on the injection pressure.
AUTHORS: Zunping Liu
Zunping Liu, Kyoung-Su Im, Yujie Wang, Kamel Fezzaa, Kathy Harkay, Vadim Sajaev, Louis Emery and Jin Wang :
Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave., Argonne, IL 60439;
Xingbin Xie, Ming-Chia Lai :
Department of Mechanical Engineering, Wayne State University, 5050 Anthony Wayne Dr, Detroit, MI 48202.
TITLE: Ultrafast X-ray Phase-Contrast Imaging of High-Speed Fuel Sprays from a Two-Hole Diesel Nozzle
ABSTRACT: Near-nozzle fuel spray morphology during high-pressure injection by axially symmetric single-hole nozzles for high-pressure diesel injection has been unveiled from recent studies. Such a study had not extended to more realistic and practical multihole injectors. This study focuses on near-nozzle spray morphology of high-speed fuel jets from a two-hole nozzle under varied injection conditions. The two-hole nozzle is a simplified version of multihole nozzle, where two orifices are symmetrically aligned around the nozzle axis. The angle between two-orifices is 135. The jet morphology of the two-hole nozzle was compared to that of the single-hole nozzle during quasi-steady injection process.
The experiment was performed with the high-intensity and high-brilliance X-ray beam available at the Advanced Photon Source (APS) in Argonne National Laboratory. The X-ray pulses have a sub-ns (150 ps) temporal duration, which is sufficiently short to minimize the motion blur of the high-speed fuel jets (>500 m/s). It was observed that turbulent flow in swirl-like morphology was formed inside fuel jets from the two-hole nozzle, while more laminar-like morphology is associated with the jets issued by single-hole nozzles. This turbulent jet flow of the two-hole nozzle led to unstable jet development, wider cone angle and faster break-up of the jet compared to the single-hole nozzle jet. At relatively low injection pressures, unstable swirl-like wavy jet flow was formed inside the two-hole nozzle jet. At higher injection pressures, more turbulent jet morphology other than wavy structures was observed inside the two-hole nozzle jet, while the jet axis was more stable compared to those at lower injection pressures.
AUTHORS: Seoksu Moon,
Zunping Liu, Jian Gao, Eric Dufresne, Kamel Fezzaa and Jin Wang, X-Ray Science Division, Argonne National Laboratory
X. Xie, M.C. Lai, Department of Mechanical Engineering, Wayne State University
Argonne National Laboratory
Xingbin Xie and Ming-Chia Lai
Wayne State University
TITLE: Discontinuous Galerkin based Level Set Scheme
ABSTRACT: In this work, the accuracy, efficiency, and robustness of level-set schemes based on discontinuous Galerkin (DG) are investigated. DG employs a high order polynomial basis to represent the transported function accurately. The polynomial reconstruction is discontinuous between cells, and with the exception of a Riemann solver at the cell faces, the solution of the equation is independent from cell to cell. These features confer to DG schemes both high order accuracy and high compactness, making them ideal candidates for resolving the highly complex topological structures often observed in turbulent two-phase flows. An additional advantage of DG in comparison to other schemes lies in the fact that higher order quantities such as the gradient or the curvature of the level set function, which play an important role in two-phase flows, are readily available.
Despite these advantages, the use of DG in level set schemes has remained scarce. In particular, the influence of the limiting step, often necessary in DG schemes, has not been analyzed. Similarly, the re-initialization step used to reset the level set function to its desired shape is challenging to implement using DG, and requires careful investigation.
In this work, a comprehensive DG strategy for level set schemes is developed. It combines a quadrature-free DG scheme for the level set transport, a recently proposed DG scheme for the Hamilton-Jacobi equation that arises in the re-initialization step, and a Hermite Weighted Essentially Non-Oscillatory (HWENO) scheme in order to limit the oscillatory nature of the solution. The influences of various design parameters of the schemes are analyzed for the target application of complex multiphase flows. In particular, special care is given to the accuracy of the curvature computation and the amplitude of the spurious currents. The robustness of the proposed approach is discussed in the presence of a turbulent flow field. Finally, the effect of DG on mass conservati
AUTHORS: Mark Czajkowski, University of Colorado at Boulder
Alireza Nejadmalayeri and Olivier Desjardins, University of Colorado at Boulder
TITLE: Experimental and Computational Study of a Spray at Multiple Injection Angles
ABSTRACT: The interaction of a spray plume within a confined cross-flow environment occurs often in spray applications, most notably in gas conditioning applications. Characterization and modeling of the drop size and velocity distributions, as well as spray shape, was conducted within a controlled wind tunnel environment. The primary focus of this study is the effect of various incident angle cross-flows on the characteristics of a spray nozzle.
While the spray characteristics immediately downstream of the nozzle will govern the significance of the effect of the cross-flow, this study aims to provide a reference case in order to guide and compare future work. A low flow rate, hydraulic, hollow cone spray was investigated with a nominally uniform cross-flow air speed of 15 m/s. These results demonstrate the trajectory change as well as the change in spray plume characteristics over a range of spray angles defined relative to a co-flow air stream.
The experimental results were acquired with a LaVision Laser Sheet Imaging (LSI) and an Artium Phase Doppler Interferometer (PDI), to measure the spray shape, size, distribution characteristics as well as droplet size and veloci-ty. The spray simulations were conducted using ANSYS FLUENT computational fluid dynamics (CFD) package in conjunction with custom spray injection methods developed in-house. The computational models agreement, and disagreement, with the experimentally acquired results provides insight for the appropriate considerations when con-structing cross-flow models.
This work builds on results and methods presented at the 2009 ICLASS conference.
AUTHORS: Kyle Bade, Spray Analysis and Research Services, Spraying Systems Co.
Wojciech Kalata, Kathleen Brown, Rudi Schick, Spray Analysis and Research Services, Spraying Systems Co.
TITLE: Exhaust Tailpipe fuel Spray Optimization and Fuel Usage Rates for Operating an Exhaust Aftertreatment System on a Heavy-Duty Diesel Engine Powered Vehicle
ABSTRACT: Please see full paper for abstract: ILASS2010-177.pdf
AUTHORS: James McCarthy, Jr., Eaton Corporation
Daniel Bamber, Steve Ambrose, Eaton Corporation
TITLE: Planar Laser Induced Fluorescence (PLIF) Flow Visualization applied to Agricultural Spray Nozzles with Sheet Disintegration; Influence of an Oil-in-Water Emulsion
ABSTRACT: A typical agricultural spray process involves atomizing a liquid stream of diluted pesticide solution through hydraulic spray nozzles that inherently produce a wide spectrum of spray droplet sizes. Finer droplets have higher potential for off-target movement or drift, which is of concern due to their potential impacts on neighboring crops and livestock, sensitive ecological resources, and human health. A factor that has been found to reduce fines production is the addition of an oil phase in the form of an oil-in-water emulsion. The mechanism of the effect is not fully understood.
The flow visualization technique Planar Laser Induced Fluorescence (PLIF) is commonly employed for characterization of scalar mixing. PLIF has also been used to characterize sprays. For this study, Rhodamine WT fluorescent dye was mixed into the solution to be sprayed. The laser sheet, aligned vertically, is passed through the exit area of the nozzle causing the droplets to fluoresce. The fluoresced pattern is imaged. For sprays, image pairs are taken on the order of 100 s apart, thus the displacement and hence velocity vectors of drops can be computed throughout the spray pattern. Additionally, the images are of sufficient quality to study liquid sheet breakup physics.
For sprays with sheet breakup, such as many fan-type agricultural sprays, PLIF is effective at measuring the velocity within the spray before, during, and after the sheet disintegration. The motion of surface features on the sheet before disintegration allow the velocity to be calculated in a similar fashion to discrete particles. Traditional Particle Image Velocimetry (PIV) can in principle work as well, however the image quality from light scattered off of the unbroken sheet in PIV was found to be inferior to images from fluoresced light generated within the sheet by PLIF.
The method was applied to fan sprays (hydraulic and air-induced) in common use in agricultural applications. Measurements were per
AUTHORS: Michael D. Cloeter, The Dow Chemical Company
Kuide Qin, Dow AgroSciences LLC, Pramod Patil, The Dow Chemical Company, Billy Smith, The Dow Chemical Company
TITLE: A level-set based methodology for modeling interfacial flows characterized by large density ratios
ABSTRACT: We introduce a numerical methodology for modeling interfacial flows characterized by large density ratio. The method uses the temporal evolution of a signed distance function, commonly employed in the level set method to represent fluid interfaces. In this method, the conservative form of the momentum equation is solved to advect momentum. To calculate the momentum fluxes at any point, we use the signed distance function at two subsequent time steps. For consistency, we use the same flux density for advecting mass, and thereby establish a tight coupling between mass and momentum transport. We present a set of results in which the density ratio ranges from 650 to 10,000, and validate the methodology against theoretical and experimental results. Finally, to demonstrate the capability of the method in handling flows with large interface deformations, we present simulations of liquid sheet breakup in shear air.
AUTHORS: Mehdi Raessi, Stanford University
Heinz Pitsch, Stanford University
TITLE: Micro-Particles Dispersion and Gas Dynamics in an Axi-Symmetric Supersonic Nozzle
ABSTRACT: This paper describes a new pain free device for micromolecular vaccine/drug delivery. The device accelerates micro solid particles to high speeds sufficient to penetrate the epidermis/dermis layer to achieve the pharmaceutical effect (cells of interest). Helium is used as the driving gas for the solid particles because of its high compressibility factor. Numerical parametric study for gas pressures ranging between 3 and 6 Mpa and gold particles of diameters
1.8 µm and 5 µm is investigated. The computed results using FINE/Turbo show that uniform particle velocity was achieved at standoff distance of 20 mm downstream of the device exit with particles concentrated on the supersonic core jet. Changing the helium pressure did not change the particles velocity but increased the gas velocity by about 16 %. Furthermore gas pressure has no effect on the particles concentration at device exit. The calculated Particle impact parameter required to insure particle penetration to breach stratum corneum was achieved for both 5µm and1.8 µm gold particles with the later has more uniform spatial distribution.
AUTHORS: Salah M. Soliman, University of Cincinnati
S. Abdallah, E. J. Gutmark and M. Turner, Dept. of Aerospace Eng. And Eng. Mechanics, PO Box 210070
University of Cincinnati, Cincinnati, OH 45221
TITLE: Mass Flux Measurement of Two Phase Dense Spray Using a Coupled Impulse Probe and PDPA Technique
ABSTRACT: Please see full paper for abstract: ILASS2010-182.PDF
AUTHORS: M.A. Rahman, University of Alberta
F. Vakili-Farahani, T. Heidrick, B.A. Fleck, University of Alberta, Ecole Polytechnique Federale de Lausanne
TITLE: The Influence of Density Ratio on the Primary Atomization of a Turbulent Liquid Jet in Crossflow
ABSTRACT: In this paper we study the impact of density ratio on liquid jet in crossflow penetration, deformation, and atomization if all other characteristic parameters, i.e. momentum flux ratio, jet and crossflow Weber and Reynolds numbers, are maintained constant.
We perform detailed simulations of the primary atomization region using the refined level set grid method to track the motion of the liquid/gas phase interface. We employ a balanced force, interface projected curvature method to ensure high accuracy of the surface tension forces, use a multi-scale approach to transfer broken off, small scale nearly spherical drops into a Lagrangian point particle description allowing for full two-way coupling and continued secondary atomization, and employ a dynamic Smagorinsky large eddy simulation approach in the single phase regions of the flow to describe turbulence.
We compare simulation results obtained previously using a liquid to gas density ratio of 10 for a momentum flux ratio 6.6, Weber number 330, and Reynolds number 14000 liquid jet injected into a Reynolds number 740,000 gaseous crossflow to those at a density ratio of 100, a value typical for gas turbine combustors. The results show that the increase in density ratio results in a noticeable increase in jet penetration and decrease in liquid core deformation in the transverse direction. Grid converged drop size distributions resulting from primary atomization show no impact of density ratio on medium size drops, but some decrease in large scale drops. Velocities of drops generated by primary atomization are reduced in the crossflow direction, but virtually unchanged in the jet and transverse direction.
AUTHORS: Marcus Herrmann, Arizona State University
TITLE: Morphology of Fuel Sprays from Single-Orifice Microhole Nozzles
ABSTRACT: Ultrafast (150ps) x-ray propagation-based phase-contrast imaging technique was used to obtain high-spatial-resolution, single-shot images of the dense diesel fuel jets in the near-nozzle region (0~6mm) issuing into a quiescent nitrogen gas ambient. Specially fabricated axial single-hole nozzles with diameters of 135 and 96 micrometers were used to inject both diesel and biodiesel at different injection pressures. The injection pressure of the fuel jet was varied between 30 and the 100 MPa while the entire injection process and the breakup of the fuel jet was investigated.
In the experiment, complex features of high-speed liquid jet in the optically dense near-nozzle region are clearly captured by the phase-contrast images, including the morphology and the dynamics. Such information cannot be obtained with any optical diagnostics due to significant scattering by the large number of droplets in this region. The results show that the jet morphology is highly sensitive to jet velocity, nozzle geometry and the physical properties of fuels. During the quasi-steady flow, the near-nozzle jet showed the transition of laminar to turbulent flow within a few mm from the nozzle exit depending on the injection conditions. The jet structures, in particular the surface wave length and break-up distance were quantitatively correlated with the injection conditions. These results will undoubtedly facilitate better understanding the atomization mechanisms of liquid jets and provide directly experimental evidence for high-fidelity computations and simulations.
This work and the use of the APS at Argonne National Laboratory were supported by the U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The work is partially supported by DOE Office of Vehicle Technology.
AUTHORS: Jian Gao, Engine Research Center, University of Wisconsin-Madison & Advanced Photon Source, Argonne National Laboratory
Zunping Liu, Seoksu Moon, Eric Dufresne, Kamel Fezzaa, Jin Wang, Advanced Photon Source, Argonne National Laboratory; Xingbin Xie, Ming-chia Lai, Wayne State University
TITLE: Computational Study of Effects of Drop Size Distribution in Fire Suppression Systems
ABSTRACT: As the use of water mist continues to gain acceptance as a practical fire suppression agent, the fire protection indus-try continues using computational fluid dynamics (CFD) to model the formation, delivery and flame interaction of water mist drops. With positive results and incredible progress, several efforts have been made over recent years to improve the fire suppression modeling techniques. However, a simulation is only as meaningful as the quality of the initial assumptions and parameters used to drive the suppression model. With this in mind, the authors incorporate a comprehensive water mist droplet characterization with realistic geometrical and parametric configuration into CFD fire suppression model.
In this study, spray simulations in fire suppression scenario were conducted using ANSYS FLUENT CFD package. The main focus for the CFD study was to assess the fire suppression sensitivity to realistic drop size distribution in cluster swirl type hydraulic atomizers. Performed analysis consisted of three different scenarios with different supply pressure conditions while keeping the suppressant at the same flow capacity. To maintain same flow rate at three pressure conditions, the capacities of the hydraulic atomizers were matched to the pressures that were rated as low, intermediate and high pressures (7, 35 and 70 bar respectively). In high pressure scenario where Volumetric Median Diameter (VMD) was the smallest, the evaporation rate was the highest and therefore the suppression process was the most efficient.
AUTHORS: Geoff Tanner, Spraying Systems Co.
Wojciech Kalata, Kathleen Brown, and Rudolf J. Schick, Spraying Systems Co.
TITLE: Estimating the Secondary Droplet Size Distribution after Micro-Explosion of Bio-Fuel Droplets
ABSTRACT: Recently, some potential alternative substitutes of petroleum fuels such as biodiesel and ethanol have received much attention because they are renewable and friendly to the environment and can possibly reduce domestic demand on foreign petroleum. Bio-fuels are generally mixed with petroleum-based diesel or gasoline in the commercial market. Since the volatilities and boiling points of ethanol and diesel/biodiesel fuels are significantly different, micro-explosion can be expected in binary mixtures of ethanol-diesel (E-D) or ethanol-biodiesel (E-B) and also in ternary mixtures of ethanol-biodiesel-diesel (E-B-D). Understanding the atomization process and dynamics of secondary droplets in bio-fuel and diesel blends due to micro-explosion is helpful in optimizing bio-fuel engine performances. In this study, a numerical model of micro-explosion in multi-component bio-fuel droplets is proposed. The onset of micro-explosion is determined by the homogeneous nucleation theory and characterized by the normalized onset radius (NOR). The bubble expansion process is described by a modified Rayleigh equation. The final breakup is modeled from a surface energy approach by imposing minimal surface energy (MSE) on the system. The MSE approach reaches the same conclusion as the model developed by Zeng and Lee, where atomization is determined by the aerodynamic disturbances. Based the simulated results of droplet characteristics at the onset of micro-explosion, together with the predictions from the breakup model, a simple way of estimating the Sauter mean radius (SMR) of the secondary droplets is proposed and verified against limited available experimental data. There exists an optimal droplet size for the onset of micro-explosion. It is concluded from the study that micro-explosion, characterized by the normalized onset radius (NOR), is possible in bio-fuel and diesel blends under engine operation conditions. Adding biodiesel, less volatile than ethanol and diesel, into the
AUTHORS: Chia-fon F. Lee, University of Illinois at Urbana-Champaign
Way Lee Cheng, Kuo-Ting Wang and Cai Shen, University of Illinois at Urbana-Champaign
TITLE: Effects of Micro-Explosion on Butanol-Biodiesel-Diesel Spray and Combustion
ABSTRACT: Blends of butanol-biodiesel-diesel were tested inside a constant volume chamber to investigate liquid spray and combustion of the fuels. With high-speed camera and synchronized copper vapor laser, spray penetration is observed. Various ambient temperatures and fuel composition were investigated. There is a sudden drop in spray penetration at 800 K and 900 K, but not at 1000 K and 1200 K. When the spray penetration of the butanol-biodiesel-diesel blends is compared to that of the biodiesel-diesel blends, under non-combusting environment, a sudden drop in spray penetration length is also observed at 1100 K. High speed imaging shows that, for the non-combusting case, at 1100 K, the tip of the spray jet erupts into a plume sometime after injection for the butanol-biodiesel-diesel blend. The same is not seen with the biodiesel-diesel blend, neither at lower ambient temperature of 900 K. It is concluded that micro-explosion can occurs under particular conditions for the butanol-biodiesel-diesel blend, and the results is consistent with previous theoretical study in the literature.
AUTHORS: Yu Liu, Ji Lin University
Way Lee Cheng, Chia-Fon F. Lee, UIUC, Jun Li, Ji Lin University
TITLE: Experimental Investigation of Droplet Dynamics and Spray Atomization inside Thermostatic Expansion Valves
ABSTRACT: Experimental investigation on spray atomization and droplet dynamics inside a thermostatic expansion valve (TEV) was conducted. A needle and an orifice were copied from a commercial TEV and machined to be mounted inside a chamber with optical access so that the flow inside the TEV is simulated and visualized at the same time. The break-up and atomization of the refrigerant were documented near the downstream of the orifice under different feed conditions on micro-second scale. A Phase Doppler Anemometry (PDA) system was used later to measure the size and velocity of atomized refrigerant droplets. It is found that spray impingement is inevitable and crucial to the atomization. Under steady-state operation, liquid film was seen formed on the needle plate and caused droplets splashed from plate, which will further have an effect on the droplets size and mass flux distribution. The before impact and after impact droplets were characterized by PDA system and for studying the impingement. In addition, the impact of the needle geometry inside the valve on refrigerant atomization has also been investigated.
AUTHORS: Ming Huo, University of Illinois at Urbana-Champaign
Chia-fon F. Lee, University of Illinois at Urbana-Champaign
TITLE: Exhaust Tailpipe fuel Spray Optimization and Fuel Usage Rates for Operating an Exhaust Aftertreatment System on a Heavy-Duty Diesel Engine Powered Vehicle
ABSTRACT: Please see full paper for abstract: ILASS2010-177.PDF
AUTHORS: James McCarthy, Jr., Eaton Corporation
Daniel Bamber, Steve Ambrose, Eaton Corporation