Begell House Inc.
Atomization and Sprays
AAS
1044-5110
13
5&6
2003
DIESEL FUEL SPRAY DROPLET SIZES AND VOLUME FRACTIONS FROM THE REGION 25 MM BELOW THE ORIFICE
425-442
10.1615/AtomizSpr.v13.i56.10
Jennifer
Labs
Division of Engineering, Colorado School of Mines, Golden, Colorado, USA
Terry
Parker
Florida Polytechnic University, Lakeland, FL 33805, USA
Droplet diameter and volume fraction measurements are reported for three different fuels (diesel fuel, dodecane, and methyl oleate) as a function of radial position within a pressure-atomized spray typical of diesel systems. Injection system parameters were peak pressures of 62 MPa and a single-orifice injector with a 0.31-mm orifice diameter and an L/D ratio of approximately 2. Results are for individual injection events into atmospheric-pressure and ambient-temperature air at an axial distance of 25 mm from the nozzle. Measurements relied on infrared scattering, which was specifically chosen due to the high droplet number densities of these sprays. Details of the measurement technique are presented along with results. Results indicate droplet diameters are the smallest at the spray centerline (2–3.25 mm), and grow with radial distance from the centerline (6–8 mm at the spray periphery). Volume fractions greater than 1% are seen at the spray centerline, and, once the spray has developed, the majority of the mass is contained in the central 0.75-mm-radial region. Spray details presented include the definition of transient time periods for the spray, the spray width as a function of time, the coupling between injection pressure and observed diameters (SMD) and volume fractions, and the differences in the spray properties as a function of fuel type.
DEVELOPMENT OF MICRO-DIESEL INJECTOR NOZZLES VIA MEMS TECHNOLOGY AND EFFECTS ON SPRAY CHARACTERISTICS
443-474
10.1615/AtomizSpr.v13.i56.20
Seunghyun
Baik
Engine Research Center and Engineering Physics, University of Wisconsin, Madison, Wisconsin, USA
James P
Blanchard
College of Engineering, University of Wisconsin - Madison
Michael L.
Corradini
Engine Research Center and Engineering Physics, University of Wisconsin, Madison, Wisconsin, USA
Micro-machined diesel injector nozzles have been designed, fabricated, and used with commercially produced diesel injection systems in the study of spray dynamics. Such a system, properly designed, may improve spray behavior in direct-injection (DI) diesel engines by improved atomization and fuel–air mixing.
In this work, 14 micro-planar orifice nozzles were fabricated using the micro-electro-mechanical-systems (MEMS) technique. Circular-orifice diameters were varied from 40 to 260 μ;m, and the number of orifices was varied from one to 169. Three plates with noncircular orifices were also fabricated to examine the effect of orifice shape on spray characteristics. These nozzles were then attached to commercial injectors and the associated injection systems were used for the spray experiments.
Given these novel injection systems, jet spray characteristics of micro-planar-orifice nozzles were investigated experimentally using optical diagnostic techniques in a pressurized constant-volume cylindrical chamber. Local drop sizes were measured by the laser diffraction technique, and average drop sizes of the whole sprays were measured by the light extinction technique. Current test results show expected qualitative trends in spray kinematics and drop sizes, but quantitative magnitudes of the behavior are less dependent on orifice geometry than first anticipated. Droplet coalescence among adjacent sprays was apparent for the multiple-orifice nozzles because all the orifices were aligned in the same direction with limited spacing. Nonplanar configurations are under development and may show improved performance.
GENERATION AND SHOCK WAVE CHARACTERISTICS OF UNSTEADY PULSED SUPERSONIC LIQUID JETS
475-498
10.1615/AtomizSpr.v13.i56.30
K.
Pianthong
School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney, Australia; Department of Mechanical Engineering, Faculty of Engineering, Ubonratchathani University, Ubonratchathani, Thailand
Brian E.
Milton
Emeritus Professor, School of Mechanical and Manufacturing Engineering The University of New South Wales Sydney, NSW 2052 Australia
Masud
Behnia
School of Mechanical and Manufacturing Engineering, University of New South Wales, Sydney 2052, Australia
One method for generating pulsed, supersonic liquid jets is by projectile impact, often referred to as the "Bowden-Brunton" method. In this article, the fundamental processes by which such jets are generated are investigated. The momentum transfer from the projectile to the liquid and the shock wave reflection within the nozzle cavity are the key items of interest. In this study, a new one-dimensional analysis has been used in order to simplify this complex and difficult problem. First, the impact pressure obtained from the projectile is derived. Then, an investigation of the intermittent pressure increase in both a closed end cavity and a simple stepped, cross-sectional nozzle cavity (sac) is carried out. The nozzle pressure and final jet velocity are estimated and compared with experimental results, with which they show good agreement, and to a previous analytical method. Also, experimental shadowgraph visualization of the jet penetrating the air is presented. Some interesting characteristics, such as a rippled leading edge main (bow) shock wave in the air and the appearance of a second shock wave, can be seen. These characteristics relate well to those anticipated by the analysis.
CATEGORIZING LINEAR THEORIES FOR ATOMIZING ROUND JETS
499-516
10.1615/AtomizSpr.v13.i56.40
Sam S.
Yoon
Mechanical Engineering Department, Korea University, Anamdong, 5-Ga, Sungbukgu, Seoul, 136-713, Korea
Stephen D.
Heister
Maurice J. Zucrow Laboratories, Department of Aeronautics and Astronautics, Purdue University, West Lafayette, Indiana, USA
This article compares and contrasts linear stability analyses based on the deformations of an infinite liquid column and due to boundary-layer vorticity imparted to the free surface from the orifice exit plane. The bulk of the prior works, which date back to Kelvin-Helmholtz [1], Rayleigh [2], Weber [3], Taylor [4], Ponstein [5], Levich [6], Sterling and Sleicher [7], and Reitz and Bracco [8], have focused on the liquid column analysis. Though used to a lesser extent, the boundary-layer instability analysis by Brennen [9] can also be used to predict the dominant wavelength of the laminar jet. Differences between the two approaches are highlighted for sample injection conditions and injector geometries.
ATOMIZATION CHARACTERISTICS OF FUEL INJECTED THROUGH THE INJECTOR OF A SI ENGINE WITH A DIRECT INJECTION SYSTEM
517-534
10.1615/AtomizSpr.v13.i56.50
Sungwook
Park
School of Mechanical Engineering, Hanyang University, Seoul 04763, Republic
of Korea
Chang Sik
Lee
School of Mechanical Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791, Republic of Korea
Macroscopic and microscopic atomization characteristics of a gasoline injector operated at high pressure in a direct-injected gasoline engine are explored both experimentally and numerically. The spray development, macroscopic analysis, and spray characteristics are investigated under the conditions of various injection pressures and spray cone angles. The quantitative spray characteristics and spray developing processes are obtained by using a phase Doppler particle analyzer and a particle motion analysis system, respectively.
The numerical study is conducted using KIVA-3 code for the same operating conditions as the experimental conditions. In order to improve the prediction accuracy, the code is modified to contain the Kelvin-Helmholtz (KH)/Rayleigh-Taylor (RT) breakup model based on the competition between KH and RT instabilities.
The results provide the influence of injection pressure and spray cone angle on the spray developing processes, spray tip penetration, and atomization characteristics such as mean droplet size and mean velocity of droplets. The predicted results of spray behavior and microscopic characteristics agree with the measured results of spray characteristics.
CHARACTERIZATION OF EVAPORATING DIESEL SPRAYS USING EXCIPLEX LASER-INDUCED FLUORESCENCE MEASUREMENTS
535-559
10.1615/AtomizSpr.v13.i56.60
T.
Kim
Engine Research Center, University of Wisconsin—Madison, Madison, Wisconsin, USA
J. B.
Ghandhi
Engine Research Center, University of Wisconsin—Madison, Madison, Wisconsin, USA
Evaporating diesel sprays were investigated in a combustion-type spray chamber using the exciplex laser-induced fluorescence method at a density of 15 kg/m3 and ambient temperatures of 800 and 1000 K. The vapor-phase exciplex fluorescence measurements were calibrated, but the liquid-phase measurements were used only to identify the liquid extent. The effects of peak injection pressure (60, 90, and 150 MPa) and nozzle hole size (140, 158, and 200 μ;m were studied. The spray penetration rate was found to be in good agreement with the Naber-Siebers model for all of the cases tested. The entrained air mass ascertained from the vapor-phase measurements was also found to agree with the model results. Radial profiles of the equivalence ratio showed significant shot-to-shot variability, but exhibited a Gaussian structure when averaged at a given downstream position and time. An overall mean equivalence ratio was obtained by normalizing the measured equivalence ratio by the cross-sectional average equivalence ratio of Naber and Siebers, and by normalizing the radial coordinate by the downstream distance. The resulting profile was Gaussian (1.2 at the peak with a 0.2 full-width half-maximum), but a progressive trend was observed with respect to the nondimensional downstream distance. This effect resulted from a slower observed decrease in the centerline equivalence ratio of the measurements compared to the model.
ENTRAINMENT CONTROL FOR LIGAMENT-CONTROLLED EFFERVESCENT ATOMIZER SPRAYS
561-577
10.1615/AtomizSpr.v13.i56.70
T. J.
Kuta
Maurice J. Zucrow Laboratories (formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, USA
Michael W.
Plesniak
Maurice J. Zucrow Laboratories (formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, USA; Department of Mechanical and Aerospace Engineering The George Washington University
Ligament-controlled effervescent atomization (LCEA) was developed as a means of reducing effervescent atomizer air-to-liquid ratios by mass (ALR) from 2% to as low as 0.75%. This reduction in ALR offers an obvious advantage in numerous applications (e.g., combustion systems because of reduced parasitic losses or paint/coating sprays because of improved penetration into corners). Reduction of ALR is a necessity for consumer product sprays because of the limited quantity of atomizing air available in a prepressurized package.
This study focused on passive control of entrainment by ligament-controlled effervescent atomizer sprays. Spray control was investigated by considering the entrainment-modifying effects of four exitorifice geometries having a common diameter of 0.38 mm but different indeterminate-origins—four-point crown, two-point crown, inclined, and stepped. Each geometry was tested at two liquid mass flow rates (0.5 and 0.6 g/s), four air-to-liquid ratios (0.75 ≤ ALR ≤ 2.0%), and four axial distances (67 ≤ x/d0 ≤ 417). Data were acquired for a single bulk liquid—water. Both the atomizing gas and the entrainment gas were dried, high-pressure air.
Steady entrainment rate and momentum rate data were used to calculate entrainment numbers, E, for sprays produced using each of the entrainment-modifying geometries. Results of this experimental investigation are summarized as follows: (1) Normalized entrainment rates (me/ml) were found to scale linearly with normalized axial distance (x/d0) and to increase with increasing ALR for all exitorifice geometries. (2) Entrainment numbers were found to increase with increasing ALR for all exitorifice geometries. (3) The four-point and two-point crowns were found to enhance entrainment by the sprays, whereas the inclined and stepped exits were found to suppress it.
A CFD ANALYSIS OF THE INFLUENCE OF DIESEL NOZZLE GEOMETRY ON THE INCEPTION OF CAVITATION
579-604
10.1615/AtomizSpr.v13.i56.80
V.
Macian
CMT-Motores Termicos, Universidad Politecnica de Valencia, Valencia, Spain
Raul
Payri
CMT-Motores Térmicos, Universitat Politècnica de València, València, Spain
Xandra
Margot
CMT-Motores Térmicos
Edificio 6D
Universitat Politècnica de València
Camino de Vera s/n
46022 Valencia. Spain
F. J.
Salvador
CMT-Motores Termicos, Universidad Politecnica de Valencia, Valencia, Spain
An extensive computational fluid dynamics (CFD) study has been performed in order to analyze the influence of nozzle geometry on the internal flow characteristics of a diesel injector. The flow through cylindrical and conical nozzles with different grades of hydro-grinding and at various needle lift positions and injection pressures was calculated to observe the individual effect of these parameters on the inception of cavitation. Most calculations were based on the assumption that the nozzle flow is axisymmetric. The set of calculations that was carried out to identify the most influential parameters for the onset of cavitation was determined by means of an experimental design technique. A correlation study was made in order to obtain a numerical expression that relates the critical cavitation number to geometric dimensions. Experiments were performed to validate both numerical calculations and conditions at which cavitation appears.
ENTRAINMENT BY CONVENTIONAL EFFERVESCENT SPRAYS
605-619
10.1615/AtomizSpr.v13.i56.90
S. G.
Bush
Maurice J. Zucrow Laboratories, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, USA
Entrainment numbers (E) for conventional effervescent atomizer-produced sprays are reported. Entrainment numbers were calculated using the expression of Ricou and Spalding [12] plus measured spray entrainment and momentum rate data determined during this study. Results showed that entrainment number increases with liquid viscosity, with atomizer exit orifice diameter, and with the combined effects of surface tension and liquid density. This is in contrast to results reported for ligament-controlled effervescent atomizer sprays [6], in which fluid physical properties had no significant effect. A possible cause for this discrepancy is the known unsteadiness of conventional effervescent sprays [11]. Dimensionally scaling entrainment numbers by liquid density and orifice diameter collapsed the majority of the data onto a single line. The modified form for E describes the entrainment behavior of conventional effervescent sprays to within 25%.