Begell House Inc.
Atomization and Sprays
AAS
1044-5110
8
2
1998
NUMERICAL ANALYSIS OF THE INFLUENCE OF THE JET BREAKUP MODEL FORMULATION ON DIESEL ENGINE COMBUSTION COMPUTATIONS
123-154
10.1615/AtomizSpr.v8.i2.10
M. C.
Cameretti
D.I.M.E. Università degli Studi di Napoli "Federico II," Naples, Italy
C.
Bertoli
Istituto Motori, C.N.R., Naples, Italy
P.
Belardini
Istituto Motori, C.N.R., Naples, Italy
The multidimensional simulation methods available today for spray motion predictions solve the spray equations (including the mass, momentum, and energy changes due to the interaction between the drops and the gas), and also consider drop collision and coalescence phenomena. The most-used breakup spray models in CFD computations are based on an analysis of the instability of a liquid column injected unbroken from the nozzle orifice (in the following WAVE model), or in an analogy between a damped spring-mass system and a liquid column (TAB model). Both models require some empirical constants.
Considering also that the mechanism that controls atomization is not yet well understood, further calculations and experimental comparisons over a range of injection conditions may be useful to improve the prediction capability of these models. In previous work, an analysis was performed to determine the influence of spray breakup model constants setting on the spray tip penetration, using the KIVA II code. The mesh size adopted was quite coarse, but typical of that used in computations of diesel engine combustion. It was outlined that both the TAB and the WAVE models are sensitive mainly to the breakup time constant value; the influence of the other model constants on the tip penetration results is minimal. In spite of the fact that the physics of the two models is very different, the best setting of the constants falls in the same range.
In the present article a further analysis of spray patterns is reported, particularly related to the spray breakup phenomenon. After a brief description of the breakup models, a sensitivity analysis of the main spray features to the model constants is presented. In addition, the numerical data of jet penetration, computed with both the TAB and WAVE models, are compared with literature data for vaporizing and nonvaporizing conditions. In order to improve the numerical predictions, a "hybrid" model is proposed, based on both the TAB and WAVE models. Finally, because the overall goal of the spray computations is to obtain a reliable simulation of the overall diesel combustion process, the influence on combustion computations of breakup modeling is also evaluated and discussed.
NONLINEAR SIMULATION OF A HIGH-SPEED, VISCOUS LIQUID JET
155-178
10.1615/AtomizSpr.v8.i2.20
J. H.
Hilbing
TRW Space & Electronics Group, Redondo Beach, California, USA
Stephen D.
Heister
Maurice J. Zucrow Laboratories, Department of Aeronautics and Astronautics, Purdue University, West Lafayette, Indiana, USA
A model has been developed to simulate the nonlinear, unsteady evolution of a high-speed viscous liquid jet issuing from a circular orifice. The model is based on a zonal approach in which an integral method is utilized for a thin viscous region at the jet periphery, while a boundary-element method is used for the inviscid "core" flow. Results indicate that steady-state solutions are possible neglecting the presence of the gas. Under these conditions, the jet "swells" in diameter and the boundary layer thins to a shear layer over a length of about half an orifice radius. Because boundary-layer relaxation is occurring during these simulations in which steady-state solutions appear, atomization mechanisms relying on this process cannot explain the observed behavior. The swelling phenomenon has the potential to explain several fundamental experimental atomization observations regarding turbulence and orifice design.
EFFECTS OF CAVITATION AND INTERNAL FLOW ON ATOMIZATION OF A LIQUID JET
179-197
10.1615/AtomizSpr.v8.i2.30
Nobushige
Tamaki
JSME, Department of Mechanical Engineering, Kinki University Takaya, Umenobe, Higashi Hiroshima, 739-2116, Japan
M.
Shimizu
Department of Mechanical Engineering, Kinki University Takaya, Umenobe, Higashi Hiroshima, 739-2116, Japan
Keiya
Nishida
Department of Mechanical System Engineering, University of Hiroshima, 1-4-1
Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan
Hiroyuki
Hiroyasu
Institute of Industrial Technology, Kinki University, Higashi-Hiroshima, Japan
The purpose of this investigation is to clarify atomization mechanism of a high-speed liquid jet issuing from a single-hole nozzle. In previous research, it was believed that atomization of the liquid jet was caused by the interfacial forces existing between the issuing jet and the surrounding gas. However, it has been determined that the strong turbulence in the nozzle hole due to cavitation phenomena contributes greatly to the disintegration of the liquid jet. In order to reveal the mutual relationships, experiments were performed under conditions ranging from decompression to high ambient pressures by using acrylic nozzles with various length-to-hole diameter ratios L/D and different inlet shapes of the nozzle hole, close to the hole diameter of an actual nozzle. As a consequence of this study, it has been determined that the primary factor in atomization of the liquid jet is the disturbance of the liquid flow resulting from cavitation phenomena.
A STUDY OF TWO-PHASE INJECTOR PERFORMANCE FOR DIRECT-INJECTION STRATIFIED-CHARGE ENGINES
199-215
10.1615/AtomizSpr.v8.i2.40
Yong-Pyo
Lee
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Taejon, Korea
Sung-Soo
Kim
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Taejon, South Korea
Sangmin
Choi
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Yusong-gu, Taejon, Korea
The application of direct-injection stratified-charge (DISC) engines has been limited by the unsatisfactory atomization performance of existing fuel injectors, although it has great possibilities for improved fuel economy and low emissions through lean combustion. A two-phase injector for DISC engines was developed, which produced a good-quality spray. Injector performance was checked to investigate the spray structure and the optimal conditions in terms of design variables and operating parameters. This air-assisted injector exhibited stable behavior at speeds up to 6000 rpm and produced a finely atomized spray of 14.9 μ;m in Sauter mean diameter.
ULTRASONIC ATOMIZATION OF LIQUIDS: STABILITY ANALYSIS OF THE VISCOUS LIQUID FILM FREE SURFACE
217-233
10.1615/AtomizSpr.v8.i2.50
Daniel
Sindayihebura
Department of Mechanical Engineering, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
Leon
Bolle
Department of Mechanical Engineering, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
One of the fundamental steps in the process of liquid film ultrasonic atomization is the hydrodynamic instability. The resulting surface waves become unstable and tear. This causes a mist of uniform droplets to be formed and ejected. The study of ideal liquid film free surface behavior in the steps prior to droplet formation leads to a stability analysis based on the Mathieu-Hill equation. Unfortunately, a similar analysis cannot realistically be developed for a viscous liquid. The present work performs a linear analysis derived from the hydrodynamics, which allows a stability analysis of viscous bounded liquid film free surface. Actual results are compared to those obtained in the case of an inviscid fluid.
ON THE STABILITY OF LIQUID SHEETS IN HOT ATMOSPHERES
235-240
10.1615/AtomizSpr.v8.i2.60
E. A.
Foumeny
Department of Chemical Engineering, University of Leeds, Leeds, UK
N.
Dombrowski
Department of Chemical Engineering, University of Leeds, Leeds, UK
It has been shown previously that the introduction of a hot gas around a thin liquid sheet causes the sheet to disintegrate through the onset of perforations. This article describes some experiments which show that this mechanism is dependent upon the initial presence of small disturbances on the sheet surface.