Experimental analysis and numerical modeling using lisa-ddb hybrid breakup model of direct injected gasoline spray

This paper presents the effect of injection pressure on the atomization characteristics of high-pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a laser sheet method. In order to investigate the atomization process in more detail, the calculations with the LISA-DDB hybrid model were performed. The results provide the effect of injection pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is revealed that the accuracy of prediction is promoted by using the LISA-DDB hybrid breakup model, comparing to the original LISA model or TAB model alone. And the characteristics of the primary and secondary breakups have been investigated by numerical approach.     

Numerical and experimental analysis of spray atomization characteristics of a GDI injector

In this study, numerical and experimental analysis on the spray atomization characteristics of a GDI injector is performed. For numerical approach, four hybrid models that are composed of primary and secondary breakup model are considered. Concerning the primary breakup, a conical sheet disintegration model and LISA model are used. The secondary breakup models are made based on the DDB model and RT model. The global spray behavior is also visualized by the shadowgraph technique and local Sauter mean diameter and axial mean velocity are measured by using phase Doppler particle analyzer. Based on the comparison of numerical and experimental results, it is shown that good agreement is obtained in terms of spray developing process and spray tip penetration at the all hybrid models. However, the hybrid breakup models show different prediction of accuracy in the cases of local SMD and the spatial distribution of breakup.     

Numerical and experimental study on hollow-cone fuel spray of highpressure swirl injector under high ambient pressure condition

A hybrid breakup model was proposed as a trustworthy prediction of hollow-cone fuel spray in the present study and the atomization process of the hollow-cone fuel spray of a high-pressure swirl injector in a Gasoline Direct Injection (GDI) engine under high ambient pressure conditions was studied by a new hybrid breakup model. The proposed hybrid breakup model is composed of the Linearized Instability Sheet Atomization (LISA) model as a primary breakup process. The Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model, instead of the Taylor Analogy Breakup (TAB) model, was used as a secondary breakup process. The effects of the droplet deformation on a droplet aerodynamic external force are considered in the APTAB model. In addition, we replaced the x ² distribution function used in previous the APTAB model by the Rosin-Rammler distribution function to improve the prediction precision. The Laser Induced Exciplex Fluorescence (LIEF) technique and the Phase Doppler Anemometry (PDA) system were used to produce a set of experimental data for the model validation. The estimation of the prediction ability of the LISA+APTAB model was carried out, and spray characteristics, which are difficult to obtain by experimental method, were calculated and discussed. The suggested hybrid breakup model showed better prediction capability compared with the previous model (LISA+TAB model). From the calculated results, the effect of the ambient pressure on the SMD (Sauter Mean Diameter) and droplet velocity could be discussed quantitatively.     

Spray characteristics on the electrostatic rotating bell applicator

The current trend in automotive finishing industry is to use more electrostatic rotating bell (ESRB) need space to their higher transfer efficiency. The flow physics related with the transfer efficiency is strongly influenced by operating parameters. In order to improve their high transfer efficiency without compromising the coating quality, a better understanding is necessary to the ESRB application of metallic basecoat painting for the automobile exterior. This paper presents the results from experimental investigation of the ESRB spray to apply water-borne painting. The visualization, the droplet size, and velocity measurements of the spray flow were conducted under the operating conditions such as liquid flow rate, shaping airflow rate, bell rotational speed, and electrostatic voltage setting. The optical techniques used in here were a microscopic and light sheet visualization by a copper vapor laser, and a phase Doppler particle analyzer (PDPA) system. Water was used as paint surrogate for simplicity. The results show that the bell rotating speed is the most important influencing parameter for atomization processes. Liquid flow rate and shaping airflow rate significantly influence the spray structure. Based on the microscopic visualization, the atomization process occurs in ligament breakup mode, which is one of three atomization modes in rotating atomizer. In the spray transport zone, droplets tend to distribute according to size with the larger drops on the outer periphery of spray. In addition, the results of present study provide detailed information on the paint spray structure and transfer processes.     

Comparison of experimental and predicted atomization characteristics of high-pressure diesel spray under various fuel and ambient temperature

The aim of this study is to investigate the effects of the fuel temperature and the ambient gas temperature on the overall spray characteristics. Also, based on the experimental results, a numerical study is performed at more detailed and critical conditions in a high pressure diesel spray using a computational fluid dynamics (CFD) code (AVL, FIRE ver. 2008). Spray tip penetration and spray cone angle are experimentally measured from spray images obtained using a spray visualization system composed of a high speed camera and fuel supply system. To calculate and predict the high pressure diesel spray behavior and atomization characteristics, a hybrid breakup model combining KH (Kelvin-Helmholtz) and RT (Rayleigh-Taylor) breakup theories is used. It was found that an increase in fuel temperature induces a decrease in spray tip penetration due to a reduction in the spray momentum. The increase of the ambient gas temperature causes the increase of the spray tip penetration, and the reduction of the spray cone angle. In calculation, when the ambient gas temperature increases above the boiling point, the overall SMD shows the increasing trend. Above the boiling temperature, the diesel droplets rapidly evaporate immediately after the injection from calculation results. From results and discussions, the KH-RT hybrid breakup model well describes the effects of the fuel temperature and ambient gas temperature on the overall spray characteristics, although there is a partial difference between the experimental and the calculation results of the spray tip penetration by the secondary breakup model.     

微量润滑系统参数对雾化特性的影响

微量润滑切削过程中,系统的雾化特性会影响界面间的雾粒渗透效果。采用激光粒度分析仪对微量润滑系统的雾化特性进行了单因素试验测试,研究了空气流量、喷射距离、切削液用量以及切削液类型等系统参数对雾粒平均直径及其尺寸分布的影响。结果表明,空气流量、喷射距离为主要影响因素,当空气流量保持在80~90 L/min、喷射距离控制在40~50 mm范围内时能够获得较好的雾化效果。基于因次分析法建立了微量润滑条件下的雾粒直径预测模型,其误差小于10%,能够较好地描述微量润滑系统参数对雾化特性的影响。     

Steady-flow characteristics and its influence on spray for direct injection diesel engine

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of Dl (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70ΰ and 90ΰ. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.     

MODELING OF A SOLID CONE PRESSURE-SWIRL ATOMIZER

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An overview of liquid spray modeling formed by high-shear nozzle/swirler assembly

A multi-dimensioanl model is being increasingly used to predict the thermo-flow field in the gas turbine combustor. This article addresses an integrated survey of modeling of the liquid spray formation and fuel distribution in gas turbine with high-shear nozzle/swirler assembly. The processes of concern include breakup of a liquid jet injected through a hole type orifice into air stream, spray-wall interaction and spray-film interaction, breakup of liquid sheet into ligaments and droplets, and secondary droplet breakup. Atomization of liquid through hole nozzle is described using a liquid blobs model and hybrid model of Kelvin-Helmholtz wave and Rayleigh-Taylor wave. The high-speed viscous liquid sheet atomization on the pre-filmer is modeled by a linear stability analysis. Spray-wall interaction model and liquid film model over the wall surface are also considered.     

Investigation of droplet size distribution in two-phase flows using a combined method for recording droplet fluorescence and diffraction scattering of light

A prototype of a combined measurement system (MS) based on the fluorescent and small-angle methods of determining the parameters of a fuel-air spray using a pulsed laser as a light source and a color digital video camera to record spray sections was designed and tested. The tests of the MS showed that it has good performance and is suitable for determining the characteristics of advanced atomizers in a pressure chamber. Spatial concentration distributions of aerosols generated by a centrifugal atomizer were studied. Distributions of time-averaged Sauter diameters of droplets, their concentration, and the circumferential inhomogeneity of droplet concentration in the spray cross section were obtained. A study of fuel atomization from a plate was performed showing the possibility of using this device in power plants to improve the atomization performance compared to the atomization of a free jet in crossflow.     

Atomization characteristics in pneumatic counterfiowing internal mixing nozzle

In an effort to illustrate the global variation of SMD (Sauter mean diameter, orD ₃₂) and AMD (Arithmetic mean diameter, orD ₁₀) at five axial downstream locations (i. e., at Z=30, 50, 80, 120, and 170 mm) under the different experimental conditions, the radial coordinate is normalized by the spray half-width. Experimental data to analyze the atomization characteristics concerning with an internal mixing type have been obtained using a PDPA (Phase Doppler Particle Analyzer). The air injection pressure was varied from 40 kPa to 120 kPa. In this study, counterfiowing internal mixing nozzles manufactured at an angle of l5^o with axi-symmetric tangential-drilled four holes have been considered. By comparing the results, it is clearly possible to discern the effects of increasing air pressure, suggesting that the disintegration process is enhanced and finer spray droplets can be obtained under higher air assist. The variations inD ₃₂ are attributed to the characteristic feature of internal mixing nozzle in which the droplets are preferentially ejected downward with strong axial momentum, and dispersed with the larger droplets which are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup by higher shear stresses at farther axial locations. The poor atomization around the centre close to the nozzle exit is attributed to the fact that the relatively lower rates of spherical particles are detected and these drops are not subject to instantaneous breakup in spite of the strong axial momentum. However, substantial increases in SMD from the central part toward the edge of the spray as they go farther downstream are mainly due to the fact that the relative velocity of droplet is too low to cause any subsequent disintegration.     

A comparative study on CFD simulation of spray penetration between gas jet and standard KIVA-3V spray model over a wide range of ambient gas densities

CFD simulation of spray penetration with standard KIVA-3V were compared with those using both an ‘original gas jet model’ and a ‘normal gas jet profile model that features a new breakup length formula’ by implementing them in the standard KIVA-3V code. The effects of entrainment coefficient on the spray penetration simulated with the gas jet profile were compared to that simulated with the standard KIVA-3V spray model. The accuracy of the CFD simulation results was estimated by comparing them with available experimental data. Both the standard KIVA-3V spray model and the normal gas jet profile model with the breakup length formula predict well the spray tip penetration up to a gas density of 60 kg/m³. The CFD simulation of spray tip penetration with the standard KIVA-3V predicts better with the ‘original gas jet model’ when the ambient gas density is lower than 60 kg/m³. For higher densities, the normal gas jet profile model with breakup length formula predicts the spray penetration better.     

Swirl effect on the spray characteristics of a twin-fluid jet

In the liquid fuel combustion chamber, employed fuel must be atomized before being injected into the combustion zone. Therefore, the complete fuel atomization is the most important condition for the combustion efficiency. The atomization quality strongly affects the combustion performance, exhaust pollutant emissions, and flame stability. Therefore, the whole process of spray atomization is of fundamental significance. During past decades many experimental and theoretical studies in this field have been carried out and some improved results have been obtained. Two-phase atomizers, having a variety of advantages such as spray uniformity, appreciable atomization, and smaller SMD with an increase of ambient gas, are considered to be applied in various industrial processes. The purpose of present study is to investigate the mean velocity, turbulence shear stress, turbulence intensity, mean drop size distribution, and droplet data rate in a two-phase swirling jet using PDPA systems.     

Atomization characteristics of emulsified fuel oil by instant emulsification

The breakup and spray formation of swirl liquid jets with respect to the instant emulsification of heavy fuel oil and water were experimentally investigated. The effects of the degree of emulsion and flashing on the macro- and microscopic spray parameters were measured optically in terms of the rotor speed, mixture ratio, and nozzle exit temperature. Enhanced emulsification and flashing improved the spray characteristics. The effect of flashing on the Sauter mean diameter of the spray decreased as the degree of emulsion increased. However, when flashing occurred, the effect of instant emulsification was small because of the blades in the emulsion chamber and filter prior to the nozzle inlet, which served as a static mixer.     

Microscopic spray characteristics in the effervescent atomizer with two aerator tubes

An experimental study is performed on atomization characteristics and stable operating conditions for the injection of high viscous waste vegetable oil using an effervescent atomizer with 2 aerator tubes. Consideration is given to the effects of ALR and liquid viscosity on the velocity and mean diameter of the injected droplet. It is found that (i) as ALR increases, the axial velocity of the droplet is increased, while half-velocity width and SMD are decreased regardless of the change in liquid viscosities, (ii) the rate of fine drop distribution occupied in the total spray field is increased with an increase in ALR, and (iii) the effect of viscosity on the atomization characteristics is minor. Consequently, it is expected that the effervescent atomizer will exhibit an excellent atomization performance at the high ALR condition, regardless of liquid viscosities.     

Spray formation by a swirl spray jet in low speed cross-flow

Breakup and spray formation of swirl liquid jets introduced into a low-speed cross-flow are experimentally investigated. Effects of the cross-flows on the macro and microscopic spray parameters are optically measured in terms of jet Weber number and liquid-to-gas momentum ratio. At lower jet Weber numbers, the liquid stream undergoes Rayleigh jet breakup. At higher momentum ratios, bag breakup occurs and tends to distort the liquid column into a loop-like structure. As the jet Weber number rises, stronger aerodynamic interaction and secondary flows cause multi-mode breakup. Regardless of the momentum ratio, the spray profile is hardly altered at higher jet Weber numbers. The cross-flow promotes the jet breakup and renders a finer spray in an entire range of injection velocities.     

Transient liquid jet breakup model and comparison with phase doppler measurements

A new liquid jet breakup model is developed based on the transient breakup mechanism and incorporated into the KIVA-II code. Liquid column is considered as a chain of balls. Rayleigh-Taylor instability and Kelvin-Helmholtz instability was applied to the liquid jet column. Liquid jet column is continuously surveyed to apply breakup mechanisms. Once liquid droplets are separated from the main liquid jet column, these droplets are subjected to the single breakup mechanism. When Bond number is greater than a critical Bond number, single droplets continue to break up by Rayleigh-Taylor instability or Kelvin-Helmholtz instability. Computational results were compared with the PDPA measurement data. Gross behavior of the spray and detailed droplet sizes and velocities predicted by KIVA calculations which include proposed drop breakup model are compared with those produced from droplet size/velocity measurements.     

Methods for Digital Particle Image Sizing (DPIS): Comparisons and improvements

This paper explores the accuracy of particle image sizing using direct processing of digitally recorded images. Traditional methods for particle image sizing were considered and, four new algorithms were developed to deliver improved accuracy and robustness. Statistical error analysis was performed using Monte Carlo simulations in order to quantify the dependence of these methods on noise, discretization, and particle size distribution. The performance of these methods were compared against Phase Doppler Analyzer measurements of spray atomization.We introduce a novel two-dimensional four-point Gaussian estimator and an alternative Gaussian estimator based on a local least squares (LLS) fit. These methods were further advanced to account for pixel discretization effects using integral formulations (continuous methods). All new methods were compared against conventional pixel counting and the established three-point Gaussian estimator. The new methods significantly reduced the total error in the diameter estimation compared to the three-point Gaussian estimator and pixel counting. The least squares Gaussian estimator and its continuous version demonstrated almost identical results and superior performance for diameters over 4 pixels. For smaller diameters, the continuous four-point Gaussian estimator delivered the highest accuracy. For uniform particle size distribution between 2–14 pixels image diameter, the least squares estimators delivered error less than 5% with respect to the true diameter for 80% of the particles. The remaining methods demonstrated error of 5% (or better) for less than 60% of the particles. Validation in an experiment of high-pressure spray atomization showed that the Gaussian local least squares methods and the continuous four-point method delivered similar particle size distribution compared to PDA. The particle mean diameter estimated by the two methods differed only by 3% and 6% respectively with respect to the PDA measurements.The novel particle image sizing schemes developed here can deliver accurate, robust, and computationally efficient apparent diameter measurement, thus providing a viable, simple and inexpensive solution for performing sizing on conventional particle image velocimetry images. This capability enables simultaneous measurements of both velocity and particle size for a wide range of multi-phase flows.     

新型细水雾灭火喷嘴的仿真及试验

为了解决细水雾喷头喷雾保护半径小的问题,研制了一种新颖的两级雾化高压细水雾灭火喷嘴。计算了索太尔雾滴直径DSM、喷嘴流速、流量和充分雾化距离。在CFD仿真中,将两级雾化喷嘴的速度场和水体积分数分布与单级雾化喷嘴的对应仿真结果分别进行对比,并优化了两级雾化喷嘴的结构参数。试验测量了DSM、喷雾速度、喷雾密度分布并和仿真结果进行对比验证。研究表明,优化设计后两级雾化喷嘴的喷雾保护半径为0.34 m,喷雾密度分布均匀;具有多喷嘴的两级雾化细水雾喷头的喷雾保护半径可以超过2 m,在消防领域具有实用价值。     

Recent progress of spray-wall interaction research

In the present article, recent progress of spray-wall interaction research has been reviewed. Studies on the spray-wall interaction phenomena can be categorized mainly into three groups: experiments on single drop impact and spray (multiple-drop) impingement, and development of comprehensive models. The criteria of wall-impingement regimes (i.e., stick, rebound, spread, splash, boiling induced breakup, breakup, and rebound with breakup) and the post-impingement characteristics (mostly for splash and rebound) are the main subjects of the single-drop impingement studies. Experimental studies on spray-wall impingement phenomena cover examination of the outline shape and internal structure of a spray after the wall impact. Various prediction models for the spray-wall impingement phenomena have been developed based on the experiments on the single drop impact and the spray impingement. In the present article, details on the wall-impingement criteria and post-impingement characteristics of single drops, external and internal structures of the spray after the wall impact, and their prediction models are reviewed.