Spray Atomization Process Research Articles

Development of a Flame Propagation Model for Dual-Fuel Partially Premixed Compression Ignition Engines

The limitations of an existing characteristic-time combustion (CTC) model are explored and a new combustion model is developed and applied to simulate combustion in dual-fuel engines in which the premixed natural gas is ignited by the combustion flame initiated by a diesel spray. The model consists of a diesel auto-ignition model and a flame propagation model. A G-equation-based model previously developed to simulate SI engine combustion was incorporated with an auto-ignition model to simulate the flame propagation process in partially premixed environments. The computer code is based on the KIVA-3V code and consists of updated sub-models to simulate more accurately the fuel spray atomization, auto-ignition, combustion, and emissions processes. Modifications were made to implement the level set G-equation approach and to track the location of the flame as a function of the turbulent flame speed, flame curvature, flow velocity, and the movement of the computational mesh in the engine environment. Good agreement with engine experiments was obtained by using the present model.

Evolution of microstructure in spray formed Al–18%Si alloy

Spray atomization and deposition process has emerged as an alternative to ingot and powder metallurgy routes. In the present investigation, we study the microstructural control during spray deposition of hypereutectic Al–Si alloy, employing different nozzle to substrate distances. Spray deposition is carried out using convergent–divergent close-coupled nozzle design at deposition distances of 200, 300, 450, and 550 mm. Microstructural characterization of oversprayed powders as well as spray formed deposits was performed. Microstructural features obtained at smaller deposition distance consist of co-existing primary Si phase and needle like eutectic Si. Dendrites of α-Al phase are observed indicating a large undercooling of the liquid pool prior to solidification. A large number of pre-solidified particles with very fine microstructure, embedded in a relatively coarse region, typically characterize those evolved at large deposition distances. However, at intermediate deposition distances, uniform and refined primary Si phases, 3–8 μm size, are observed. An undercooling effect is manifested in both the spray deposits as well as powder particles. These microstructural features have been discussed in light of a proposed model, which describes the presence of two layers (1) solidification layer and (2) interaction layer in the liquid pool.

Evolution of microstructure in spray formed Al?18%Si alloy

Spray atomization and deposition process has emerged as an alternative to ingot and powder metallurgy routes. In the present investigation, we study the microstructural control during spray deposition of hypereutectic Al–Si alloy, employing different nozzle to substrate distances. Spray deposition is carried out using convergent–divergent close-coupled nozzle design at deposition distances of 200, 300, 450, and 550 mm. Microstructural characterization of oversprayed powders as well as spray formed deposits was performed. Microstructural features obtained at smaller deposition distance consist of co-existing primary Si phase and needle like eutectic Si. Dendrites of α-Al phase are observed indicating a large undercooling of the liquid pool prior to solidification. A large number of pre-solidified particles with very fine microstructure, embedded in a relatively coarse region, typically characterize those evolved at large deposition distances. However, at intermediate deposition distances, uniform and refined primary Si phases, 3–8 μm size, are observed. An undercooling effect is manifested in both the spray deposits as well as powder particles. These microstructural features have been discussed in light of a proposed model, which describes the presence of two layers (1) solidification layer and (2) interaction layer in the liquid pool.

Cyto-Fluid Dynamic Theory of Atomization Processes

A universal theory of spray atomization processes is proposed. Based on the proposed theory, previously reported empirical models and analogy models such as the TAB model and the OPT (oval-parabola trajectory) model can be derived along with their arbitrary constants. Moreover, this theory provides a detailed formulation for breakup phenomena after two droplets collide. Finally, it is shown on the basis of this theory that the atomization processes of fuel coming from ancient living systems are similar to cell proliferation mathematically. The integrated research including liquid atomizations and actual biological cell divisions will bring us ways out of impasses for each field, since the target of both research fields is faster breakup of hydrocarbon droplets.

The Spray Structure of Air-Shrouded Dual-Stream Port Fuel Injectors With Different Air-Mixing Mechanisms

An experimental study of the spray structure from air-shrouded dual-stream injectors with different air mixing mechanisms was carried out extensively to understand the spray characteristics of dual-stream port injectors for applications to four-valve gasoline engines. The injectors were tested under both steady and transient conditions at different injection pressures and air shrouding pressure differentials. The global spray structure was visualized using the planar laser Mie scattering technique and spray atomization processes were characterized by the phase-Doppler anemometry method. The experimental results showed that spray atomization characteristics are improved markedly by the air-shrouding technique and also strongly dominated by the air-mixing mechanisms. When the air flows into the injector tip mainly from the radial direction, two streams of the spray are forced to merge together and as a result a single-stream spray is formed. When the radial velocity component of the air is reduced and the air is made to mix well with the fuel inside the injector tip, however, the two streams of the spray are well separated over different injection conditions. Moreover, other spray parameters are also modified by the air shrouded into the injector, which must be optimized in order to achieve the best performance of the air-shrouded injector.

Investigation of thermal residual stresses in layered composite using the finite element method and X-ray diffraction

A SiC particulate-reinforced 2024Al matrix composite was fabricated using a spray atomization and codeposition process to produce a layered macrostructure. The thermal macro- and microresidual stresses that develop in this layered 2024Al/SiC composite during cooling from the codeposition temperature to ambient temperature were studied using thermoelastoplastic finite element analysis. The calculated residual stresses from finite element method were compared with those obtained from X-ray diffraction (XRD), and good agreement was observed between them. The macroresidual stress distribution was very distinct for the Al and the SiC-rich layers. The macroradial stress was tensile in the Al layers and compressive in the SiC-rich layers. The macroaxial stress was found to be compressive in the vicinity of the center region of the spray-deposited material and to have mostly a continuous distribution in the Al and the SiC-rich layers. The magnitude of the macroaxial stress was noted to decrease with increasing deposition thickness from the bottom. In addition, the spray-deposited material exhibited the highest macro-von Mises’ stress around the outer edge of the deposited material. The microradial stress was in a compressive state in the SiC particulate and in the Al matrix in the vicinity of the SiC particulate. The SiC particulate exhibited compressive microhoop stress, whereas the Al matrix exhibited tensile microhoop stress. The micro-von Mises’ stress was of the highest value at the interface between the SiC particulate and the Al matrix.

The effect of ceramic reinforcement on residual stresses during spray atomization and Co-deposition of metal matrix composites

The objective of the present study is to investigate the thermal residual stresses that develop in MMCs fabricated from spray atomization and co-deposition process, using a thermo-elastoplastic finite element analysis. In order to analyze the effect of reinforcement on the residual stresses, the analysis is also performed in the material without reinforcement. In the present study, the effect of reinforcement volume fraction on the residual stresses is investigated as well.

Analysis of solidification in the spray atomization process

Spray atomization is a process for the production of net or near net shape products. In this process, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semisolidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. High rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during fight in the inert atmosphere. In this paper, a mathematical formulation for spray atomization, based on classical nucleation and growth theory and kinetics, is presented. The model deals with the following: the production of metallic droplets by high pressure inert gas atomization, including the droplet-gas interaction and the resulting droplet size distribution; the expected mode of nucleation of the solid phase, correlated to the droplet size; the thermal and solidification histories of the droplets in flight. The influence of the process parameters, such as the atomization gas pressure, the wetting angle, the geometrical features of the atomizer and feeding crucible, the distance between the atomization nozzles and the substrate, on the final microstructure is evaluated. As a result of this analysis, the optimal choice of the process parameters can be made, for the production of the desired microstructure.

Synthesis of titanium carbide from titanium oxide and carbon black: L. M. Berger, (Fraunhhofer Institution of Ceramic Technology, Dresden, Germany)

The development of spray atomization and collection processes, i.e. Osprey, consolidated spray deposition (CSD) and liquid dynamic compaction (LDC) was motivated by the severe problems of oxide contamination associated with quenched reactive metal powders as well as by the need to minimize the overall number of processing steps from the liquid metal to fully dense product, perhaps in the near-net shape state. So far, these techniques have been successfully applied to numerous aluminum-, magnesium-, nickel- and iron-based alloys, yielding attractive combinations of properties, which include improvements in tensile strength, axial fatigue strength, fatigue crack growth resistance, superplasticity and magnetic properties. Furthermore, experimental and mathematical modeling studies have shown that the aforementioned property improvements depend on the production of a rapidly solidified, microstructurally homogeneous material during spray deposition. In turn, the achievement of such structures depends on the characteristics of the atomized droplets in flight and on impact, i.e. droplet size and distribution, relative proportions of solid and liquid, temperatures, droplet velocities, dendrite arm spacings, degree of undercooling etc. The purpose of this paper is to review the more important findings over the past decade of spray atomization and collection studies.

Spray-atomized and codeposited 6061 Al/SiCp composites

Spray atomization and codeposition processes have received considerable attention for the synthesis of discontinuously reinforced metal-matrix composites. This methodology involves the mixing of reinforcements and matrix under thermal conditions such that the matrix contains both solid and liquid phases. In principle, such an approach avoids the extreme thermal excursions, with concomitant degradation in interfacial properties and extensive macrosegregation, normally associated with casting processes. Furthermore, this approach also eliminates the need to handle fine reactive particulates normally associated with powder metallurgical processes. To investigate the utility of this process for the preparation of metal-matrix composites, several silicon carbide particulate-reinforced 6061 Al composites were prepared. The spray-atomized and codeposited materials exhibited attractive combinations of strength, elastic modulus and elongation, although further work is needed to optimize their properties.

Effects of geometry and position of the metal delivery tube on ultrasonic gas atomization

The effects of the geometry and the position of the metal delivery tube on the pressure condition in the gas-metal interaction zone were studied. The measurements were performed under conditions which simulated ultrasonic gas atomization experiments, but at low gas atomization pressures (50–200 psig, 345–1380 kPa). Low gas atomization pressures are used in spray atomization and deposition processes such as liquid dynamic compaction (LDC), and Osprey. Depending on the experimental conditions, either underpressure or overpressure in the metal delivery tube was detected. The magnitude of the underpressures and overpressures was found to increase with the gas atomization pressure; the maximum pressure differences with respect to the atomization tank pressure were about 3 psi (21 kPa) when argon was used as an atomization gas with a pressure of 200 psig (1380 kPa). Underpressure or overpressure effects of such magnitude have a large effect on the metal flow rate during gas atomization. The large pressure differences measured in the present work result from using an atomizer with gas jet diameters larger than those used in previous investigations. Using a large ultrasonic atomizer, argon gas flow rates of about 5 kg/min can be obtained for atomization pressures of 200 psig (1380 kPa).