Begell House Inc.
Atomization and Sprays
AAS
1044-5110
19
3
2009
EFFECT OF OPERATING CONDITIONS AND FUEL VOLATILITY ON DEVELOPMENT AND VARIABILITY OF SPRAYS FROM GASOLINE DIRECT-INJECTION MULTIHOLE INJECTORS
207-234
10.1615/AtomizSpr.v19.i3.10
Z.
van Romunde
Department of Mechanical Engineering, University College London,Torrington Place, London WC1E 7JE, UK
Pavlos
Aleiferis
Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, United Kingdom
Maximum benefits from gasoline direct-injection systems can only be achieved by precisely controlling the atomization and evaporation processes of the fuel within the cylinder of an internal combustion engine. These requirements place considerable demands on the fuel injection hardware, in particular the injector. In addition the variable conditions of fuel properties, fuel temperature, and in-cylinder pressure interact to affect the fuel spray formation and development. This work seeks to understand and quantify these interactions and their working mechanisms for the latest generation of direct-injection gasoline multihole injectors by examining the fuel spray in a static rig in which each of these parameters can be independently altered. Five types of fuels with different grades of volatility were studied for a range of fuel temperatures (20−120° C) and gas pressures (0.55.0 bar). The fuels included various grades of gasoline, iso-octane, and a multicomponent model fuel blended specifically to mimic gasoline but also suitable for in-cylinder laser-induced fluorescence measurements. The fuel pressure was kept constant at 150 bar throughout the experiments. Measurements of key spray parameters (such as plume penetration and cone angle) showed that the main mechanism affecting spray development in a quiescent environment was dependent on the amount of superheat of the lowest volatility components in the fuel for the prevailing gas pressure and fuel temperature conditions. A high amount of superheat led to the rapid and disruptive, near-spontaneous, vaporization of the fuel as it was ejected from the nozzle. The migration of fuel vapor to the low-pressure regions between the spray plumes acted to draw the plumes together to form a single, high-penetration-rate plume in the extreme case. This contraction of the global spray form has been termed "spray collapse." The lack of high superheat and the single boiling point of iso-octane was manifested in markedly different, less collapsed spray form, which carries implications when characterizing an engine or injector using only such a single-component model fuel. The variability of the fuel spray from injection to injection was not affected appreciably by operating conditions, suggesting a certain level of "random" small variability due to the injection event and spray breakup itself, or from injector internal effects.
ESTIMATION OF THE BREAKUP LENGTH FOR A PRESSURE-SWIRL SPRAY FROM THE EXPERIMENTALLY MEASURED SPRAY ANGLE
235-246
10.1615/AtomizSpr.v19.i3.20
Seoksu
Moon
Department of Mechanical Engineering, Inha University, Incheon, South Korea
Choongsik
Bae
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Gusong-dong, Yuseong-gu, Daejon, 305-701, Republic of Korea
Essam
Abo-Serie
The breakup length of a pressure-swirl spray was simply estimated using two analytical models and the measured spray angle due to the difficulty in determining the breakup length either numerically or experimentally. A film model, derived from the balance of forces acting on the liquid film, was employed to understand the initial film flow development before breakup. The film divergent angle, which represents the radial penetration of film before breakup, was obtained using this film model at different axial locations. The input parameters for the film model, such as liquid film thickness, flow angle, and Weber number (We), were experimentally obtained using a microscopic imaging system. A droplet trajectory model was employed to analyze the droplet motion after breakup. This model assumed that the droplet moves freely after breakup with its initial axial and tangential velocity. The droplet divergent angle was defined to analyze the increase in the axial and radial distances of a droplet compared to that of the liquid film. By analyzing the droplet trajectory model, it was found that the asymptotic value of the droplet divergent angle was the same as the flow angle at the breakup location. Therefore, the spray angle was determined by adding the flow angle at the breakup location with the film divergent angle at the breakup location. By linking the film model and droplet trajectory model, the breakup length was estimated using the measured spray angle obtained by the macroscopic spray images. The estimated breakup length showed a similar value to that estimated from the linear instability analysis.
INFLUENCE OF VORTEX FLOW AND CAVITATION ON NEAR-NOZZLE DIESEL SPRAY DISPERSION ANGLE
247-261
10.1615/AtomizSpr.v19.i3.30
A.
Andriotis
Research Centre for Energy and the Environment, School of Engineering and Mathematical Sciences, City University London, Northampton Square, EC1V 0HB, UK
Manolis
Gavaises
School of Mathematics, Computer Science, and Engineering, City University London, Northampton Square, EC1V 0HB London, UK
High-speed visualization of the cavitation structures formed inside single- and multihole transparent replicas of nozzles used with low-speed two-stroke diesel engines has been performed simultaneously with the near-nozzle spray dispersion angle resulting from the atomization process of the injected liquid. The nozzle designs investigated incorporate cylindrical as well as tapered holes. The two-phase nozzle flow structures appear in two distinct forms, referred to as geometric-induced cavitation and dynamic or string cavitation. Cylindrical holes induce cavitation while tapered holes suppress it, although cavitation strings have been monitored in all nozzle types. Comparison between cylindrical and tapered nozzles in the absence of string cavitation has allowed the influence of geometric cavitation to be quantified, while acquisition of high-speed images has allowed for comparison between images in the absence and presence of cavitation strings to be made. In addition, information is provided for the variation of the spray cone angle expressed in terms of the probability of finding dispersed liquid along the spray cone and its distribution function for the different nozzle designs. The results indicate a significant increase in the spray angle in the presence of cavitation strings that is more significant in the absence of geometric cavitation.
AN APPRAISAL OF SWIRL ATOMIZER INVISCID FLOW ANALYSIS, PART 1: THE PRINCIPLE OF MAXIMUM FLOW FOR A SWIRL ATOMIZER AND ITS USE IN THE EXPOSITION AND COMPARISON OF EARLY FLOW ANALYSES
263-282
10.1615/AtomizSpr.v19.i3.40
John Joss
Chinn
School of Mechanical, Aerospace, and Civil Engineering, University of Manchester,
University of Manchester Institute of Science and Technology (UMIST), Sackville Street, M60 1QD, UK
In a number of early works involving a simple mathematical, analytical treatment of swirl atomizers, the diameter of the air core within the outlet was determined by the assumption that the air core will adjust itself for optimum flow. This is a minimum entropy condition and is termed the "principle of maximum flow." This is by analogy to the principle of maximum flow as applied to weirs (or "spillways"), where the height and velocity of the water passing over the weir adjusts itself for optimum flow. In these early works the principle of maximum flow was referred to, or mentioned, but not presented, or proven, for the swirl atomizer. Because present-day researchers often refer to these early works, this article sets out to clarify the simplified flow physics made in these inviscid analyses and demonstrate that the principle of maximum flow can indeed be applied to swirl atomizers, in principle, under their inherent limiting, simplifying assumptions. This explanation assists in comparing the early inviscid analyses, one with another, to conclude that they are intrinsically similar.
AN APPRAISAL OF SWIRL ATOMIZER INVISCID FLOW ANALYSIS, PART 2: INVISCID SPRAY CONE ANGLE ANALYSIS AND COMPARISON OF INVISCID METHODS WITH EXPERIMENTAL RESULTS FOR DISCHARGE COEFFICIENT, AIR CORE RADIUS, AND SPRAY CONE ANGLE
283-308
10.1615/AtomizSpr.v19.i3.50
John Joss
Chinn
School of Mechanical, Aerospace, and Civil Engineering, University of Manchester,
University of Manchester Institute of Science and Technology (UMIST), Sackville Street, M60 1QD, UK
Several methods of deriving an expression for the spray cone half-angle of a swirl atomizer are presented. Expressions found in the literature, based on the inviscid theory, together with suggestions for improvements, are given. The theoretically derived functions for air core diameter and discharge coefficient as functions of atomizer constant that were presented in Part 1 of this article series are charted and compared with experimental results from the literature. Also, the various functions for spray cone half-angle, as a function of the atomizer constant, are charted and compared with the experimental results from the literature. The fit of these theoretical functions with the experimental results are discussed in terms of the flow physics and the limitations of the inviscid theory. This comparison leads to the conclusion that the inviscid theory may be of benefit in the basic understanding of the flow physics of swirl atomizer internal flow. However, it is of limited value for detailed understanding of the complicated flow regime as it does not consider variations in the supply pressure, viscosity, turbulence, wall effects, or fluid-gas interactions. It does allow ballpark estimates for flow rate and for air core size.
COMMENTS ON "AN APPRAISAL OF SWIRL ATOMIZER INVISCID FLOW ANALYSIS, PART 1: THE PRINCIPLE OF MAXIMUM FLOW FOR A SWIRL ATOMIZER AND ITS USE IN THE EXPOSITION AND COMPARISON OF EARLY FLOW ANALYSES," BY J. J. CHINN
309-310
10.1615/AtomizSpr.v19.i3.60
Sung P.
Lin
Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, New York