Begell House Inc.
Atomization and Sprays
AAS
1044-5110
16
4
2006
VELOCITY MEASUREMENTS BY LASER FLOW TAGGING IN THE DENSE REGION OF DIESEL SPRAYS
349-364
10.1615/AtomizSpr.v16.i4.10
Stephan
Wissel
Lehr- und Forschungsgebiet, Laser-Messverfahren in der Thermofluiddynamik, Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, Schinkelstraße 8, D-52062 Aachen, Germany
Gerd
Grünefeld
Laser Diagnostics in Thermo-fluid-dynamics, RWTH Aachen University, Germany
The applicability of the laser flow tagging technique is investigated for velocity measurements in the liquid phase of diesel sprays. This is done under atmospheric and near-engine-like boundary conditions in a constant volume chamber. Measurements are conducted in the primary breakup zone of the spray, where other optical techniques like particle image velocimetry or phase Doppler anemometry cannot be applied. A phosphorescent tracer dissolved in the model fuel is excited by a short UV laser pulse. By means of an appropriate optical setup, phosphorescent tag lines are generated in the spray. Using an image-intensified charge-coupled device (CCD) camera, the displacement, and therefore the velocity, of the tagged droplets is determined.
ELLIPSOIDAL DROPLET DETECTION USING RANDOMIZED HOUGH TRANSFORM
365-378
10.1615/AtomizSpr.v16.i4.20
Y. J.
Choo
Department of Mechanical Engineering, Chonnam National University, 300, Yongbong-Dong, Buk-Gu, Gwangju, 500-757, Korea
Bo-Seon
Kang
Chonnam National University, Korea
In this study, an image processing program was developed to deduce parameters of the elliptic shapes of liquid droplets using the randomized Hough transform and parameter decomposition. Partially overlapping droplets were separated during a shape detection process. Five parameters of an ellipse were calculated by dividing these parameters into two groups, namely, the center position and the remaining parameters (major and minor axis lengths and axis orientation), which is known as the parameter decomposition method. Candidate ellipse centers were determined by using the geometric properties of ellipses. The standard and randomized Hough transforms were applied to locate centers and to determine the values of the remaining parameters in two and three dimensions, respectively, instead of the five dimensions originally required. Best ellipse estimations were then determined for several candidate ellipses by comparing original droplets with ellipses constructed using the estimated parameters. The developed program was applied to simulated overlapping ellipses, to real overlapping droplets, and finally, to real spray droplets. The results obtained using the developed method were satisfactory, unless there were inherent problems with the original images. This method can be also used as an effective means of separating overlapping small particles.
ATOMIZATION OF GEL PROPELLANTS THROUGH AN AIR-BLAST TRIPLET ATOMIZER
379-400
10.1615/AtomizSpr.v16.i4.30
Shai
Rahimi
RAFAEL/MANOR Propulsion and Explosive Systems Division, Haifa, Israel
Benveniste
Natan
Faculty of Aerospace Engineering, Technion − Israel Institute of Technology,
Haifa 320003, Israel
An effort was made to relate the rheological properties of gel propellant simulants with their atomization behavior. The gels were atomized using a triplet impinging air-blast atomizer. The experimental investigation demonstrates that pseudoplastic water gels exhibit spray patterns that resemble those of Newtonian liquids, but they are more difficult to atomize. The Sauter mean diameter decreases along the injector axis and increases with increasing radial coordinate and the angle between the gas jets plane and the horizontal plane. Wide-angle convergent injectors require lower upstream pressure to achieve the same atomization performance with straight injectors. Sauter mean diameter decreases down to a minimum constant value with the increase of the air-to-liquid mass flow rate ratio. Sauter mean diameter increases with increasing gellant content due to the respective increase of the shear viscosity. An expression relating the Sauter mean diameter to the injection conditions and the mean apparent viscosity at the injector exit is presented.
ELECTRICAL PERFORMANCE OF CHARGE INJECTION ELECTROSTATIC ATOMIZERS
401-420
10.1615/AtomizSpr.v16.i4.40
A. R. H.
Rigit
Faculty of Engineering, University of Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
John S.
Shrimpton
Energy Technology Research Group, School of Engineering Sciences, University of Southampton,
Atomization and Sprays Research Group Dept. Mechanical Engineering, UMIST, Manchester, United Kingdom, SO171BJ
The parametric evaluation of the variables that define the operation of a charge injection electrostatic atomizer is described in terms of the electrical performance. Here atomizer performance for smaller orifice diameters and more viscous liquids than previously investigated is presented. The response of the injected current as a function of atomizer geometry, coupled to an analysis of the empirical charge injection laws, is used to relate the electrohydrodynamics with more well-established studies in quiescent liquid. Evaluation of spray and leakage current to injection current ratios are also used to determine the electrical efficiency with a view to locating the optimum operating conditions as a function of atomizer geometry and applied bulk flow. The optimum electrode-to-orifice diameter ratio in previous work is confirmed, and the relationship between the spray specific charge and the maximum electric field on jet surface at a critical point of operation is extended to charge injection atomizers of small orifice diameter.
SPRAY CHARACTERISTICS OF CHARGE INJECTION ELECTROSTATIC ATOMIZERS WITH SMALL-ORIFICE DIAMETERS
421-442
10.1615/AtomizSpr.v16.i4.50
John S.
Shrimpton
Energy Technology Research Group, School of Engineering Sciences, University of Southampton,
Atomization and Sprays Research Group Dept. Mechanical Engineering, UMIST, Manchester, United Kingdom, SO171BJ
A. R. H.
Rigit
Faculty of Engineering, University of Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
Here the characteristics of charged sprays of insulating liquids generated by an improved charge injection (electrostatic) atomizer design are described, and the experimental database previously available in the literature is extended to a smaller range of orifice diameters and to more viscous liquids. Previously identified “subcritical” and “supercritical” electrohydrodynamic (EHD) regimes for the atomizer are confirmed to be present for the viscosity and orifice diameter ranges studied here, showing that these EHD regimes appear to be generic to the atomization method. The jet breakup dynamics and length are qualitatively and quantitatively studied using imaging and phase Doppler anemometry (PDA), and the general spray plume characteristics are quantitatively described in terms of droplet velocity and diameter probability density functions (PDFs). Radial spray charge and mass flow rates are quantified as using a purpose-built collecting system. By appropriately normalizing the data, the degree of self-similarity between different spray data sets is clearly evident and proves that the near-axis droplets are poorly charged and that the mean specific charge increases with radial displacement, again in a self-similar manner.
SCALING LAWS FOR FREE TURBULENT GAS JETS AND DIESEL-LIKE SPRAYS
443-474
10.1615/AtomizSpr.v16.i4.60
Jose M.
Desantes
CMT-Motores Termicos, Universitat Politecnica de Valencia, 46022, Spain
Jean
Arregle
CMT-Motores Térmicos, Universidad Politécnica de Valencia, Camino de Vera, s/n. 46022 Valencia, Spain
J. Javier
Lopez
CMT-Motores Térmicos, Universidad Politécnica de Valencia, Camino de Vera, s/n. 46022 Valencia, Spain
Andreas
Cronhjort
Scania CVAB, Advanced Combustion. Engine Development, SE - 151 87 Södertälje, Sweden
Scaling laws for free turbulent gas jets and diesel-like sprays are deduced and experimentally validated. The analysis is based on basic conservation equations and experimental evidence. As a new contribution, the effect of the Schmidt number on the scaling laws is analyzed and included, which leads to a more general set of normalized parameters. By analyzing the scaling laws, it is possible to obtain a clear comprehension of gas-jet or diesel-spray behavior, as well as an understanding of the relationship between input and output parameters. Two new parameters are introduced that characterize mass and momentum transfer in the radial direction of the gas jet or diesel spray, thus providing valuable information about the mixing process.