Begell House Inc.
Atomization and Sprays
AAS
1044-5110
7
6
1997
THE STRUCTURE OF AN ACOUSTICALLY FORCED, DROPLET-LADEN JET
561-579
10.1615/AtomizSpr.v7.i6.10
Tait R.
Swanson
School of Mechanical & Materials Engineering, Washington State University, Pullman, Washington, USA
Cill D.
Richards
School of Mechanical & Materials Engineering, Washington State University, Pullman, Washington, USA
A detailed characterization of the interaction of a polydisperse spray with large-scale vortical structures in a jet is presented. Phase Doppler interferometry is used to acquire droplet size and velocity information. Planar imaging techniques are applied to document the distribution of droplets and their number density within structures. The presence of large-scale structures results in large local variations of droplet number density. Images taken through the cross section of a large-scale structure provide evidence that azimuthal structures contribute to the dispersion of droplets. Size measurements show that, in general, only droplets with Stokes number less than unity are found on the outer edge of vortical structures. However, even for very small droplets (Stokes number < 0.1), a substantial portion of the vortex center is void of droplets. Radial velocity measurements show that droplets have an outward radial velocity on the leading edges and an inward radial velocity on the trailing edges of structures. Axial velocity measurements show complex size-velocity correlations within structures among different droplet size classes. Size-velocity correlations become less distinct across the jet due to the transport of droplets by large-scale vortical structures.
APPLICATION OF THE RNG k-ε MODEL TO THE ANALYSIS OF FLOWS AND SPRAY CHARACTERISTICS
581-601
10.1615/AtomizSpr.v7.i6.20
Hei Cheon
Yang
Faculty of Mechanical and Automotive Engineering, Yosu National University, 195 Kuk-Dong, Yosu, Chonnam, 150-749, Korea
Hong Sun
Ryou
School of Mechanical Engineering, Chung-Ang University, Chung-Ang University 221, HeukSuk Dong, DongJak Ku, Seoul, 156-756, Korea
K. B.
Hong
Department of Mechanical Engineering, Aju University, Suwon, Korea
H. S.
Kim
Department of Mechanical Engineering, Aju University, Suwon, Korea
Sang Kyoo
Park
Faculty of Mechanical and Automotive Engineering, Yosu National University, 195 Kuk-Dong, Yosu, Chonnam, 150-749, Korea
This article studies the applicability of the renormalization group (RNG) k-ε model to analysis of flows with spray characteristics. Predicted results using the (RNG) k-ε model of three complex flows, i.e., flow over a backward-facing step and over a blunt flat plate, and flow around a semi-3D model car, are compared with those from the standard k-ε model and experimental data. The results of the spray characteristics in the chamber of a direct-injection model engine are compared with those from the modified k-ε model and experimental data. The results of reattachment length, separated eddy size, and average surface pressure distribution using the RNG k-ε model show more reasonable trends compared with the experimental data than results using the k-ε model. The eddy viscosity predicted using the modified k-ε model in the spray region is significantly larger than that using the RNG k-ε model. Spray tip penetration predicted using the RNG k-ε model is closer to the experimental data than that using the modified k-ε model. The application of the RNG k-ε model seems to have some potential for simulations of spray characteristics, e.g., spray tip penetration, spray tip velocity, and droplet distribution, over the modified k-ε model.
ANALYTICAL PREDICTION OF THE EXIT FLOW OF CAVITATING ORIFICES
603-616
10.1615/AtomizSpr.v7.i6.30
David P.
Schmidt
Department of Mechanical and Industrial Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, USA
Michael L.
Corradini
Engine Research Center and Engineering Physics, University of Wisconsin, Madison, Wisconsin, USA
When studying sprays, it is often desirable to have a simple model of the nozzle exit. Typically, the cavitating nozzle exit velocity profile is assumed to be slug flow. In order to provide a simple yet more accurate model, an analytical description of cavitating nozzle exit flow is constructed. First, an existing model for the mass flow rate through the nozzle is rederived and compared with experimental data. Then, using a momentum balance and neglecting momentum transfer to the walls, the momentum flux through the orifice exit is calculated. An expression for the effective cross-sectional area of this exit flow and for its effective velocity is presented. The predictions of this zero wall shear model are compared to experimental velocity and drop size data and to predictions from a multidimensional CFD code. The agreement between the predictions and data suggests that this model can be used as a simple representation of the connection between the cavitating nozzle and the downstream spray. The zero wall shear model is considerably more accurate than modeling the cavitating nozzle exit condition as slug flow.
POSSIBILITY OF REDUCTION OF NOx EMISSION BY SHAPING THE MICROSTRUCTURE OF ATOMIZED OIL
617-627
10.1615/AtomizSpr.v7.i6.40
R.
Wilk
Institute of Thermal Technology, Technical University of Silesia, Konarskiego, Poland
A.
Szlek
Institute of Thermal Technology, Technical University of Silesia, Konarskiego, Poland
This article presents a method of NOx emission abatement which is a result of the bifractional atomization of oil. If, in the atomized oil, the dominating fraction of the finer droplets and the smaller fraction of the larger droplets occur simultaneously, the larger droplets are the reducing fuel for NOx. This idea was verified in an experiment by burning light oil with pyridine by means of a burner equipped with a Danfoss nozzle and two air nozzles. The stream of primary air allowed it to create the needed microstructure of the droplet population. It has been ascertained that about 30% of the reduction of the NOx concentration took place without noticeable increase in the products of incomplete combustion.
FUEL DELIVERY IN A PORT FUEL INJECTED SPARK IGNITION ENGINE
629-648
10.1615/AtomizSpr.v7.i6.50
R. M.
Wagner
Department of Mechanical and Aerospace Engineering and Engineering Mechanics, University of Missouri—Rolla, Rolla, Missouri, USA
L. M.
Nemecek
Department of Mechanical and Aerospace Engineering and Engineering Mechanics, University of Missouri—Rolla, Rolla, Missouri, USA
James A.
Drallmeier
Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, USA
The goal of this study was to investigate the effects of injector characteristics and injection timing on fuel mass delivery to the valve in a fired spark ignition engine. The relationship between injection timing and fuel arrival at the intake valve must be known for designing an injection system for increased liquid entrainment into the gas phase and minimized fuel wetting of the port walls. Fuel spray behavior from a conventional injector design and prototype vacuum-assist and air-assist injector designs is investigated by measuring fuel drop size and velocity at the intake valve using phase Doppler interferometry. The results of this study indicate the amount of time required for the fuel spray to reach the intake valve is constant and independent of injection timing. However, the width of the temporal fuel spray arrival distribution is a strong function of injection timing. Injection timing and the corresponding gas-phase dynamics have the strongest impact on the smallest drops, resulting in a redistribution of the drops with respect to size. In addition, the fuel spray behavior was investigated at the start of the intake valve event when hot cylinder gases flow into the intake port. The arithmetic mean diameter of the fuel film atomized off the back of the intake valve during this period was found to range from 55 to 65 μ;m.
MICROBUBBLE MEDIUM: PRODUCTION AND HYDRODYNAMIC PROPERTIES
649-661
10.1615/AtomizSpr.v7.i6.60
Igor V.
Chernyshev
Department of Computational Mechanics, Volgograd State University, Volgograd, Russia
Some aspects of production of gas-liquid bubble systems with very small bubbles (micro-bubble medium) are discussed. Using photographic measurements and dispersed analysis, parameters of a microbubble medium are determined (bubble mean diameter ≈ 40 μ;m). Results of simple hydrodynamic experiments with this medium are described. Measurements of the drag coefficient of a solid ball in the microbubble medium were performed at Reynolds number from 0.1 up to 2.2 × 104 and with gas void fraction less than 2.5%. Flow of the microbubble medium in horizontal tubes was investigated under conditions in which the air fraction and the Reynolds number were between 0.0% and 0.7%, and between 103 and 2.5 × 104, respectively.
MODELING ATOMIZATION PROCESSES OF PRESSURE-SWIRL HOLLOW-CONE FUEL SPRAYS
663-684
10.1615/AtomizSpr.v7.i6.70
Zhiyu
Han
State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, China; Huai'an Industrial Technology Research Institute, Huai'an, China
Scott E.
Parrish
General Motors Global R&D, 30500 Mound Road, Warren, MI, 48090-9055, USA
Patrick V.
Farrell
Engine Research Center, University of Wisconsin—Madison, Madison, Wisconsin, USA
Rolf D.
Reitz
Engine Research Center, University of Wisconsin-Madison, Rm 1018A, 1500 Engineering Drive, Madison, Wisconsin 53706, USA
A sheet spray model is proposed to study the atomization and breakup processes of hollow-cone fuel sprays resulting from pressure-swirl injectors which have potential for use in direct-injection gasoline engines. Atomization is described using a method whereby “blobs” that represents the liquid sheet outside the injector nozzle are injected with sizes equal to the sheet thickness. Breakup of the blobs and the subsequent drops is modeled using a modified Taylor analogy breakup (TAB) model in which the originally used χ-squared size distribution for the breakup drops is replaced by a Rosin-Rammler distribution for the hollow-cone sprays considered, since the former distribution was found to result in an overestimated population of large drops. The model is implemented in a multidimensional computer code and used to study pressure-swirl atomized sprays. Detailed comparisons of computed and experimentally determined spray characteristics such as spray structures, spray tip penetrations, drop sizes, and their distribution are made, and good levels of agreement are obtained.
Indices to Volume 7
685-696
10.1615/AtomizSpr.v7.i6.80