Begell House Inc.
Atomization and Sprays
AAS
1044-5110
12
1-3
2002
MODELING OF GASOLINE SPRAY IMPINGEMENT
1-27
10.1615/AtomizSpr.v12.i123.10
C. X.
Bai
Department of Mechanical Engineering, Imperial College of Science, Technology and Medicine, London, U.K.
H.
Rusche
Department of Mechanical Engineering, Imperial College of Science, Technology and Medicine, London, U.K.
A. D.
Gosman
Imperial College London Exhibition Road, London SW7 2BX, England
This article is concerned with aspects of gasoline spray droplet impingement simulation, for which an improved model has been developed for predicting the outcomes of spray droplets impacting on a wall. The model is assessed by simulating experiments on oblique spray impingement in a wind tunnel. This is done with the aid of a specially devised procedure for deducing the specification of initial droplet sizes and velocities at the gasoline injector from downstream measurements. The calculated wall spray characteristics show favorable agreement with the measurements.
BRACHIAL BURNING AND GASIFICATION SPLIT OF A CONVECTING TWO-DROPLET SYSTEM
29-47
10.1615/AtomizSpr.v12.i123.20
Wei-Hsin
Chen
Department of Environmental Engineering and Sanitation, Foo Yin Institute of Technology, Taliao, Kaohsiung Hsien, Taiwan 831, Republic of China; National Cheng Kung University
Brachial burning and gasification-split characteristics of two droplets situated in a forced convection are analyzed by means of numerical method. For the given droplet size ratios of 1.5 and 0.25, it is found that a tri-brachial burning in the former and a penta-brachial burning in the latter are exhibited, where the brachial burning and gasification split are defined according to the envelope flame formation and destruction. When the droplet size ratio is large, the two droplets are always enclosed together in a flame for low Reynolds numbers. As Reynolds numbers are higher, the flame is destroyed and brought to deposition behind the two droplets. Two or three gasification-split points are induced in accordance with the Reynolds number undergoing, thereby producing the tri-brachial burning. On the other hand, for a lower droplet size ratio such as 0.25, under certain conditions the flame surrounds only the trailing droplet, yielding a semienvelope flame. As a result, two extra brachial burn ing based on the variation of the semienvelope flame are defined, and the penta-brachial burning is obtained. Accordingly, the multiple burning states around two interactive droplets, including pure vaporization, wake flame, transition flame, envelope flame, and semienvelope flame, are established, except for the low Reynolds numbers in which only envelope flame develops. The new findings presented in the present article provide comprehensive insight for the development of droplet model in spray combustion, by intrinsically considering the variations of the Reynolds number around droplets.
BREAKUP AND ATOMIZATION OF A KEROSENE JET IN CROSSFLOWAT ELEVATED PRESSURE
49-67
10.1615/AtomizSpr.v12.i123.30
Julian
Becker
DLR—German Aerospace Center, Institute of Propulsion Technology, Cologne, Germany
Christoph
Hassa
German Aerospace Center−DLR, Institute of Propulsion Technology, Linder Hohe, 51147 Cologne, Germany
The breakup, penetration, and atomization of a plain jet of kerosene jet A-1 fuel in a nonswirling crossflow of air 'were investigated experimentally at test conditions relevant to lean, premised, pre-vaporized (LPP) combustion for gas turbines. Measurement techniques employed include time-resolved shadowgraphs, Mie-scattering laser lightsheets, and phase Doppler anemometry (PDA). The nozzle diameter was 0.45 mm and its L/D ratio was 1.56. Air velocities lay between 50 and 100 m/s, the air pressure range extended from 1.5 to 15 bar, and the air temperature was around 290 К. Fuel flow rates were chosen so that the fuel-to-air momentum flux ratio q(= rliqU2liq/rairU2air assumed mainly values between 2 and 18. Two different mechanisms of jet breakup could be discerned, and correlations for the jet penetration and lateral dispersion close to the nozzle were derived. Furthermore, the penetration of the spray plume and its representative droplet diameters were determined. Finally, a simple, approximate model to predict liquid fuel penetration is presented.
CHARACTERIZATION OF A RESIDENTIAL FIRE SPRINKLER USING PHASE DOPPLER INTERFEROMETRY
69-90
10.1615/AtomizSpr.v12.i123.40
John F.
Widmann
Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland USA
The results of a feasibility study to determine if the water sprays produced by residential fire sprinklers can be accurately characterized using phase Doppler interferometry (PDI) are presented. The large size of the water drops produced by fire sprinklers, and the relatively large coverage area of the spray, present significant challenges when attempting to characterize these sprays. These difficulties are especially relevant when using PDI because large drops and large coverage areas may result in trajectory-dependent scattering errors and attenuation of the transmitting laser beams. For the residential sprinkler investigated, it was determined that trajectory ambiguity was not a significant source of error, hut attenuation of the laser beam resulted in overcounting of drops due to burst splitting. The effect on the data was minimized by carefully choosing the operating parameters of the PDI processing electronics. For the spray investigated, the Sauter mean diameter varied from approximately 360 to 560 mm. Integration of the radial profile of the volume flux resulted in a calculated flow rate that agreed with the flow through the sprinkler to within 8%. The results of this study demonstrate that PDI can be used to accurately characterize the sprays produced by residential fire sprinklers.
SPREADING ANGLE AND CENTERLINE VARIATION OF DENSITY OF SUPERCRITICAL NITROGEN JETS
91-106
10.1615/AtomizSpr.v12.i123.50
Michael
Oschwald
DLR German Aerospace Center, Lampoldshausen, Baden-Württemberg, 74239,
Germany
The atomization of a cryogenic nitrogen jet has been investigated under thermodynamic conditions typical/or high-pressure LOX/GH2 rocket combustors. At these cryogenic high-pressure conditions the injected fluid is near its critical point. Jet spreading angles and the variation of the centerline density downstream of the injector have been determined from density profiles obtained from spontaneous Rатап measurements. The results are compared with experiments and models describing the limiting cases of gas jet atomization and the disintegration of liquid sprays.
EXPERIMENTAL STUDY AND NEURAL NETWORK MODELING OF THE LIGAMENT DISINTEGRATION IN ROTARY ATOMIZATION
107-121
10.1615/AtomizSpr.v12.i123.60
Gunther
Schulte
Chemical Engineering Department, University of Bremen, Bremen, Germany
Stephan
Sternowsky
University of Bremen, Bremen, Germany
Roberto
Guardani
Chemical Engineering Department (LSCP), University of Sao Paulo, Sao Paulo, Brazil
Claudio A. 0.
Nascimento
Chemical Engineering Department (LSCP), University of Sao Paulo, Sao Paulo, Brazil
An experimental study of the droplet sizes generated by a liquid ligament emerging from a rotary atomizer is described. A high-speed-shutter CCD camera was used to observe the ligament path, the ligament thinning, and the breakup. Droplet sizes were measured with laser diffraction technique. The atomizer consisted of a rotating drum with a small orifice at the lateral surface. Due to the experimental setup, the radial and tangential velocity components of the emerging ligament can be varied independently. The experimental work was carried out with variation of rotational speed, mass flow rate, and fluid composition (mixtures of water, glycerol, and surfactant). A neural network (NN) was applied to model and simulate the droplet diameter for different operating conditions, showing good agreement with the measured values. Based on the NN predictions of the system behavior, the model was used as a tool to detect outliers in the experimental data.
STABILITY BOUNDARIES OF LAMINAR PREMIXED POLYDISPERSE SPRAY FLAMES
123-143
10.1615/AtomizSpr.v12.i123.70
J. Barry
Greenberg
Aerospace Engineering, Technion, Israel Institute of Technology (IIT), Haifa 32000,
Israel
A simple model of a flame front propagating through a fuel-rich droplet—vapor—air mixture is presented. An arbitrary polydisperse size distribution of droplets in the spray is allowed. The droplets are permitted to vaporize at a finite rate so that their interaction with and possible traversal of the flame front is accounted for. Steady-state solutions are established by means of large activation energy asymptotics. An analysis of instability to transverse perturbations is then carried out in order to determine neutral stability boundaries.
Two initial droplet size distributions having the same Sauter mean diameter (SMD) are considered. One is initially quasi-monodisperse (A), whereas the second is bimodal (B). It is found that the onset of flame cellularization is sensitive to the initial droplet size distribution in the spray. Specifically, under certain operating conditions, the flame resulting from distribution A is cellular, whereas that of distribution B is stable. Under other conditions, in which both spray flames are unstable, the cellular structure of flame A is found to be finer than that of flame B. These results indicate that use of the SMD to characterize a spray in the context of cellular flame instability may lead to mistaken conclusions. However, the location of the pulsating stability boundaries was found to be rather insensitive to the initial droplet distribution and, indeed, to the presence of the droplets. In addition, it lay beyond the practical range of Lewis numbers relevant to these rich flames.
SPRAY EVAPORATION
145-161
10.1615/AtomizSpr.v12.i123.80
Milan
Marcic
University of Maribor, Maribor, Slovenia
This article describes a fuel jet injected at high pressure into ambient air. A new liquid fuel content measuring method was developed to detect fuel quantity on the basis of droplet electrical charge. The fuel is electrically charged as a result of its rubbing against the injection nozzle's metal parts. Numerous tests have confirmed that the electrical charge is a good indication of liquid fuel content and proved good linearity and reliability for this new method. The radial liquid fuel distribution in the spray was measured at various points from the injection nozzle. The first cross section was located at a distance of 10 mm and each subsequent cross section at a further distance of 10 mm. The results of the measurements showed that the liquid fuel concentration was the highest on the spray axis and that it declined in the radial spray direction. The quantity of evaporated fuel across each cross section is calculated from the measured liquid fuel quantity and the total injected fuel volume.
A PREFERENTIAL VAPORIZATION MODEL FOR MULTICOMPONENT DROPLETS AND SPRAYS
163-186
10.1615/AtomizSpr.v12.i123.90
Yangbing
Zeng
Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Illinois, USA
Chia-Fon
Lee
School of Mechanical Engineering, Beijing Institute of Technology, Beijing
100081, China; Department of Mechanical Science and Engineering, the University of Illinois
at Urbana-Champaign, Champaign, IL 61801, USA
A multicomponent vaporization model for spray computations was developed to account for the temperature and concentration nonuniformity inside a droplet due to preferential vaporization and finite diffusion processes. The effect of internal circulation was also included using effective diffusivity. The model was validated through rigorous tests and the results agreed well with accurate finite-difference solutions for temperature temporal variations of nonvaporizing droplets and with the measured mole fraction temporal variations of bi-component droplets. The model was also applied to investigate the vaporization of solid-cone sprays and physical insights on preferential vaporization were revealed. Throughout the tests, comparisons with the widely used infinite diffusion model (limited accuracy, low computational cost) and the simplified vortex model(high accuracy, high cost) were also made. Overall, the accuracy of the present model is close to that of the simplified vortex model, while the computational cost is comparable to that of the infinite diffusion model.
THE SPRAY-INDUCED FLOW AND ITS EFFECT ON THE TURBULENT CHARACTERISTIC COMBUSTION TIME IN Dl DIESEL ENGINES
187-208
10.1615/AtomizSpr.v12.i123.100
Franz X.
Tanner
Department of Mathematical Sciences, Michigan Technological University, Houghton, MI
49931, USA
Rolf D.
Reitz
Engine Research Center, University of Wisconsin-Madison, Rm 1018A, 1500 Engineering Drive, Madison, Wisconsin 53706, USA
In direct-injection diesel engines the combustion process is strongly influenced by the turbulence of the spray-induced flow. This flow is transient in nature and, therefore, the equilibrium-based k-e-type turbulence models yield inaccurate predictions of the turbulence mixing time scales. This requires adjustments of the turbulence characteristic combustion time by means of the coefficient CM, in order to match experimental cylinder pressures of different engines. These adjustments are explained in terms of nonequilibrium turbulence behavior of the spray-induced flow. A relation between the spatially averaged equilibrium and nonequilibrium turbulence time scales is derived which leads to a scaling law between the different engines. In particular, the value of CM for one engine can be obtained from the optimum CM of another engine, provided the turbulence determining integral length scales are known. This scaling behavior has been demonstrated for four substantially different engines by comparing the tuned values of CM with the computed scaling factors, and favorable agreement has been obtained.
EFFECT OF INJECTION GAS DENSITY ON COAXIAL LIQUID JET ATOMIZATION
209-227
10.1615/AtomizSpr.v12.i123.110
E.
Porcheron
Laboratoire de Combustion et de Detonique, UPR 9028 au CNRS, ENSMA, Universite de Poitiers, Futuroscope Cedex, France
Jean-Louis
Carreau
Institut PPRIME, Département Fluides, Thermique, Combustion, CNRS ENSMA Université de Poitiers UPR 3346, ENSMA BP 109, 86960 FUTUROSCOPE Cedex, France
D.
Le Visage
Laboratoire de Combustion et de Detonique, UPR 9028 au CNRS, ENSMA, Universite de Poitiers, Futuroscope Cedex, France
Francis
Roger
Institut PPRIME, Département Fluides, Thermique, Combustion, CNRS ENSMA Université de Poitiers UPR 3346, ENSMA BP 109, 86960 FUTUROSCOPE Cedex, France
This work deals with the effect of injected gas density on the characteristics of the liquid core observed at the exit of the injection element used for cryogenic propulsion. The study was conducted at atmospheric pressure both in water/air and in liquid oxygen/inert gas. The techniques used are visualization, optical fiber probe, and a phase Doppler system. In keeping with our predictions, we show that for a constant momentum flux ratio J between the gas and the liquid, the higher the gas jet density is, the more the gas jet is capable of atomizing the liquid jet efficiently. A correlation of the liquid presence probability (LPP) on the jet axis, which implies notably J and the density ratio between the gas and the liquid, gathers the results obtained in simulation fluids and in a liquid oxygen jet, with good agreement.
A COMPARISON OF SPRAY CHARACTERISTICS BETWEEN AN AIR-ASSISTED FUEL INJECTOR AND A HIGH-PRESSURE SWIRL INJECTOR FOR GASOLINE DIRECT-INJECTION ENGINE APPLICATION
229-245
10.1615/AtomizSpr.v12.i123.120
C.
Jang
Precision Instrument R&D Center, Samsung Techwin Co., Ltd., Sungnam City, Kyungki, Korea
The spray characteristics of two preferred injection tools for gasoline direct-injection (DI) application were compared. An air-assisted fuel injector (AAFI) and a high-pressure swirl injector (HPSI) were designed and fabricated, and the characterization strategies and processes for both injector sprays were arranged in parallel. In this article, the overall spray characteristics, defined as spray pattern, penetration, internal spray structure, atomization performance and drop size distribution, are discussed. A spray shape factor is introduced to describe the development of intermittent sprays from both injectors. Axial penetration appears to be almost linear in the case of the AAFI, while its instantaneous speed continuously decreases with time in the HPSI. Large droplets are distributed at the tail end of the AAFI spray, while they are concentrated on the head portion of the HPSI spray. From the viewpoint of mean drop diameter, feasible ranges of injection and of ambient pressure are found to be broader in the HPSI. Drop size distributions of the HPSI are found to be more uniform than those of the AAFI.
NUMERICAL SIMULATION OF DROPLET FORMATION FROM COAXIAL TWIN-FLUID ATOMIZER
247-266
10.1615/AtomizSpr.v12.i123.130
Takao
Inamura
Graduate School of Science and Technology, Hirosaki University, Japan
Masatoshi
Daikoku
Department of Mechanical Engineering, Hachinohe Institute of Technology, Hachinohe-shi, Aomori-ken, Japan
A breakup model of a liquid jet issuing from a coaxial twin-fluid atomizer is proposed. The breakup of a liquid jet is modeled using the modified jet-embedding (JE) technique. An intact core is separated into several control volumes and the conservation equations of mass and momentum of an individual element are solved. In the proposed model, the spray generated from the liquid jet surface has a distribution in which the droplet number decreases monotonically as the drop size increases. Along the liquid jet intact core, Sauter mean diameter (SMD) has a peak in the vicinity of the atomizer exit. The atomization rate decreases gradually along the center axis. The calculation tendencies of breakup length with air velocity are coincidental with those of the measurements, but the effects of air velocity on the breakup length in calculations are smaller than those of the measurements. As the air velocity increases, the total SMD decreases rapidly and the total atomization rate is almost constant. From comparisons of calculations to empirical equations, the calculations fall between two empirical equations, except at small air velocity. The airflow and the droplet behavior are calculated by a SIMPLER algorithm and PSI-cell model using a newly proposed breakup model. The radial distribution of the SMD has a peak which moves to the peripheral as it goes downstream. The droplet velocity in the center of the liquid jet is smaller than the air velocity in the vicinity of an atomizer exit. At a certain position, the relationship between the air and droplet velocities is reversed.
CONVERSION OF DROPLET SIZE DISTRIBUTIONS FROM PMS OPTICAL ARRAY PROBE TO MALVERN LASER DIFFRACTION
267-281
10.1615/AtomizSpr.v12.i123.140
Milton E.
Teske
Continuum Dynamics, Inc., Ewing, New Jersey, 08543, USA
Harold W.
Thistle
Forest Health Technology Enterprise Team USDA Forest Service 180 Canfield St., Morgantown, West Virginia, 26505, USA
Andrew J.
Hewitt
Stewart Agricultural Research Services, Macon, Missouri, USA
I. W.
Kirk
USDA Agricultural Research Service, College Station, Texas, USA
This article considers the practical conversion of droplet size spectra data from Particle Measurement Systems (PMS) optical array probe (temporal, or number-flux weighted, sampling) to Malvern laser diffraction (spatial, or number-density weighted, sampling). PMS data collected from two wind tunnels are compared with Malvern data collected from a third. The resulting transformation is applied to the historical USDA Forest Service droplet size distribution database (PMS measurements), in an effort to provide data consistent with the Spray Drift Task Force droplet size distribution database found in AgDRIFT® (Malvern measurements).
TWO-STEP START TRANSIENTS WITH LONG FEEDLINES DISCHARGING LIQUID THROUGH SHARP-EDGED CYLINDRICAL NOZZLES
283-297
10.1615/AtomizSpr.v12.i123.150
K.
Ramamurthi
Thermodynamics and Combustion Laboratory, Indian Institute of Technology, Madras, Chennai 600036, India
R.
Patnaik
Propulsion Research and Studies Group, Liquid Propulsion Systems Centre, Trivandrum, India
Start transients of liquids flowing through sharp-edged cylindrical nozzles in a feedline nozzle
assembly are investigated. A quasi-steady regime of reduced flow rate is shown to precede the full
flow when the nozzle flow velocities are near the threshold values corresponding to the inception of
cavitation. The duration of the diminished quasi-steady flow is further seen to correspond to the
characteristic response time of the nozzle—feedline assembly. The disturbances generated during the
characteristic response time of the system are shown to advance the onset of the cavitated flow and
give rise to the initial phase of reduced flow rate.
THE INFLUENCE OF VISCOELAST1C FLUID PROPERTIES ON SPRAY FORMATION FROM FLAT-FAN AND PRESSURE-SWIRL ATOMIZERS
299-327
10.1615/AtomizSpr.v12.i123.160
Günter
Brenn
Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology,
8010 Graz, Austria
M.
Stelter
Lehrstuhl fur Stromungsmechanik, University of Erlangen-Nurnberg, Eriangen, Germany
Franz
Durst
FMP TECHNOLOGY GMBH, Am Weichselgarten 34, 91058 Erlangen, Germany
The formation of sprays of viscoelastic polymer solutions from flat-fan and pressure-swirl atomizers •was investigated experimentally. The fluids were characterized rheologically by means of a novel elongational device which allows the relaxation time and the steady terminal elongational viscosity of the fluids to he measured. These quantities turned out to be significant for the breakup of ligaments and drop formation from рrefilming atomizers. The elongational device furthermore quantifies differences between flexible and rigid polymers. With this rheological information and by means of dimensional analysis, the global nondimensional Sauter mean diameter of sprays from the flat-fan and the pressure-swirl atomizers is represented universally as a function of characteristic numbers. With the help of the same characteristic numbers, the volume fractions of small droplets in the sprays are quantified. These results are the basis of a design method for, e.g., agricultural sprays, where small fractions of small drops in the drop size spectra are required.
THEORETICAL INVESTIGATION ON VARIABLE-DENSITY SPRAYS
329-358
10.1615/AtomizSpr.v12.i123.170
Arturo
De Risi
Dipartimento di lngegneria dell'Innovazione, Universita di Lecce, Lecce, Italy
T.
Donateo
Dipartimento di lngegneria dell'Innovazione, Universita di Lecce, Lecce, Italy
D.
Laforgia
Dipartimento di lngegneria dell'Innovazione, Universita di Lecce, Lecce, Italy
The aim of the present investigation is the analysis of the influence of liquid-fuel compressibility on the simulation of sprays produced by high-pressure injection systems. Two different equations have been introduced in the K1VA3V code to calculate liquid-phase density. The first one determines fuel density by using a second-order function of drop temperature and pressure, while the second one also takes into account the quantity of air dissolved in the fuel. Breakup, vaporization, and collision models as well as the energy, momentum, and air-spray mass exchange equations were modified so that each droplet would have a different density, according to its position and evolution.
A comparison between experimental and numerical data for sprays injected in a constant-volume vessel at ambient temperature and pressure has been carried out to test the practical capability of the modified KIVA3V subroutines. The predicted and measured results of penetration versus time and drop size distribution showed good agreement. An in-depth study of the influence of gas temperature on the droplet vaporization rate has been performed for a single droplet and for sprays injected in a high-temperature, medium-pressure, constant-volume chamber. The effect of fuel density variability on vaporizing noncombusting sprays has been investigated for both models. The air dissolved in the fuel was found to affect liquid-phase density only at low ambient pressure.
Finally, the experimental data measured on a small-bore diesel engine have been used to verify the provisional capabilities of constant- and variable-density models. NO and soot predictions have shown to be dependent on the model used for liquid-phase density.