Linearized Instability Sheet Atomization Research Articles

Prediction of droplet size distributions from a pre-orifice nozzle using the Maximum Entropy Principle

The atomized droplet size distribution (DSD) produced by a nozzle is a fundamental information to define the performance of application systems. In this paper a new model to represent the atomization of a pre-orifice nozzle is presented. It is based on the Maximum Entropy Principle (MEP), the Linearized Instability Sheet Atomization (LISA) model and Computational Fluid Dynamics (CFD) simulations. Different atomization liquids with varied physical properties were sprayed at different pressures and their droplet size distributions were measured for model calibration and validation. The LISA model correctly predicts the effect of the pressure and physical properties of the mixtures on the most probable droplet diameter. The CFD studies allow to predict the influence of the flowrate on the energy source term of the MEP energy balance, which is not negligible. On the other hand, based on the LISA model, the calculated momentum source term does not impact on the DSD prediction significantly. The developed model, which just includes two adjustable parameters, is able to well represent experimental DSDs from a pre-orifice nozzle operating at different pressures.

Spray in cross–flow: comparison of experimental and numerical approach

The spray behaviour and droplet trajectories in realistic conditions are of crucial importance in many industrial, agricultural and chemical applications. Droplet characteristics and spray trajectory in chemical applications (e. g. flue gas scrubbing, CO2 capture in spray column) determine the amount of mass involved in the gas scrubbing process, mass trapped by the flow or attached to the walls. Knowledge of the droplet behaviour can improve a nozzle design and scaling, increase the process efficiency, minimize the process liquid and blow away the fraction. In this study, experiments with pressure swirl nozzle in cross–flow of air were performed at one nozzle injection pressure (0.5 MPa) and several cross–flow velocities (8, 16, 32 m/s). The results on droplet trajectories are compared with numerical results obtained by ANSYS Fluent. Two Lagrange approaches for spray modelling were used. Injection of droplet groups and Linearized Instability Sheet Atomization (LISA) model incorporated within ANSYS Fluent were used to represent the spray. The CFD results of spray penetration and droplet trajectories are compared with experimental data. A simple analytical model is able to well predict trajectories of large droplets, but fails to predict trajectories of small droplets. The LISA model yields a better accuracy for spray in cross-flow prediction.

Numerical and experimental analysis on spray characteristics of biodiesel (waste cooking oil) using pressure swirl atomizer

Atomization characteristics and evaporation have major role in air-fuel mixing and the combustion process in diesel engine. The aim of this study is to perform numerical and experimental analysis to investigate the spray pattern of biodiesel (waste cooking oil) generated from pressure swirl atomizer. The computation exhibits Eularian-Lagrangian method to comprise flow of multiphase and also linearized instability sheet atomization (LISA) model to envisage atomization, sheet breakup, and film formation. The model's strength is the identification structure of spray created from pressure swirl atomizer. A three-dimensional computational fluid dynamics work consisting of LISA and Taylor analogy breakup model are certified via experimentation taken from constant volume chamber. Further, spray tip penetration, cone angle, and sauter mean diameter (SMD) are identified for fuel (B100, B25, and D) under injection pressure of 110 and 160 MPa, and 2.8 MPa ambient pressure using swirl atomizer in constant volume chamber. This particular spray is quite important for application in diesel engines but is not extensively explored. The results reveal that as injection pressure increases from 110 MPa to 160 MPa. The spray tip penetration for B100, B25, and D are increased by 19.86%, 14.90%, and 14.50% respectively, further, cone angle at the start of injection decreases by 6%, 5%, and 3.41%, similarly, the average SMD decreases by 25%, 33.33%, and 25.4%, respectively. This is due to the rheological property of fuel, turbulent energy of droplet and air is maximum in primary breakup zone.

Effects of the physical properties of fuel on spray characteristics from a gas turbine nozzle

Abstract In a gas turbine combustion system, droplet distribution in the combustor directly affects the combustion process. Fuel droplet size and droplet velocity determine the fuel droplet distribution in the combustor. The present study aims to investigate effects of physical properties on spray characteristics using computational fluid dynamics (CFD) analysis. Spray modeling was performed to analyze the spray characteristics for different fuel physical properties. The hollow cone spray of a gas turbine nozzle was modeled using a LISA (Linearized Instability Sheet Atomization)-TAB(Taylor Analogy Breakup) model with commercial CFD code called, ANSYS Fluent 16.2. The model was validated against the experimental results, which were obtained by PDPA (Phase Doppler Particle Analyzer) and spray tomography. Based on this spray model, the effect of fuel physical properties on spray characteristics were determined. In addition, because the spray patterns differed various injection fluids, the spray characteristics of the gas turbine nozzle with various injection fluids were considered from the perspective of fuel physical properties. It was found that higher density, viscosity and surface tension delayed the atomization process and that density and surface tension have a more significant effect on spray atomization, than viscosity in the catastrophic breakup regime.

Numerical and experimental study on the spray characteristics of full-cone pressure swirl atomizers

Numerical and experimental studies have been performed to investigate the macroscopic spray structure and spray characteristics of sprays generated by a full-cone pressure swirl atomizer. The simulation employs Eulerian-Lagrangian scheme to account for the multiphase flow and the linearized instability sheet atomization model to predict film formation, sheet breakup and atomization. Reynolds-Averaged Navier–Stokes (RANS) equations are solved for turbulent gas flow. The model predictions show great consistency with the experimental measurements of the spatial variation of the droplet size and velocity obtained from Phase Doppler Particle Analyser (PDPA). The robustness of this model makes it useful to predict the structures and characteristics of co-flow sprays produced by pressure-swirl atomizers. This particular spray is quite important in spray cooling application but is not extensively studied. The study reveals that the entrainment effect and intense central-region atomization cause small droplets to concentrate on the spray axis and large droplets to dominate in the peripheral region of the spray. This finding is consistent with the observation that turbulence kinetic energy of air is maximum near the nozzle exit, where atomization is intense and momentum exchange is strong, and gradually decreases in both radial and axial directions. Moreover, the drops inside the full cone are relatively small, and evaporate more easily than their large counterparts in the peripheral region, hence removing substantial sensible heat from surrounding air and creating low-temperature region in the central of the spray.

CFD Modeling of Kerosene Combustion with Various Initial Conditions and Fuel Droplet Diameters

This paper presents the numerical models for the analysis of combustor fuel spray, characteristics, invarious injection conditions in a can type of combustor with a double stage radial swirler. Spray consists of twofundamental and consecutive steps, means the primary breakup and the secondary breakup. The primary breakupis modeled by Linearized Instability Sheet Atomization (LISA) which are mostly used in a pressure swirlatomizers. Secondary breakup is modeled by Taylor analogy breakup model (TAB). The trajectory and velocityof generated fuel droplets is determined by Lagrangian Particle Tracking. Characteristics of jet breakup, dependson a variety of factors such as turbulence, injection pressure drop, velocity profiles, nozzle geometry, and thephysical state of the liquid fuel. In this paper Jet-A aviation fuel (kerosene), modeled as a two-componentsurrogate fuel (by mass 60 % C10H22 and 40 % C9H12). The standard k–e model with the enhanced walltreatment and the Euler-Lagrange method were employed for the simulation of the turbulence and spray. Allresults of the simulation in this paper are analyzing in 3 various injection conditions and one of these cases waschosen and implemented in a real annular combustion chamber of a gas turbine. A PDF Flamelet model wasemployed to simulate combustion process.

Numerical Simulation of Pressure-Swirl Spray Dispersion by Using Eulerian-Lagrangian Method

To gain a general understanding of atomization and sheet breakup processes, the interaction of pressure-swirl hollow-cone sprays and a quiescent medium was investigated computationally. The spray characteristics of Iso-octane (n-C8H18) with high pressure-swirl injector in the ambient conditions are modeled. The Linearized Instability Sheet Atomization (LISA) model has been used to describe the primary breakup processes of the spray. Sauter Mean Diameter, sheet thickness and exit velocity were computed as the results of primary breakup. Disintegration of large drops is simulated using Taylor analogy breakup (TAB) model in which the Rosin-Rammler distribution is used. Evaporation and collision models are deactivated in this study. The model considers the transient behavior of the pre-spray and steady-state behavior of the main spray for three various injection pressures and liquid mass flow rates. Qualitative and quantitative comparisons between the simulated and experimentally measured results were made. The numerical simulations can successfully demonstrate the spray characteristics, such as spray tip penetration, drop sizes and overall spray structure.

Computational Fluid Dynamics Modeling of a Fluid Catalytic Cracking Atomizer

A new two-phase atomizer used in the fluid catalytic cracking (FCC) process which has recently been studied experimentally, is modeled in three dimensions in a lagrangian framework by using a computational fluid dynamics (CFD) method. Special emphasis is placed on the study of the liquid atomization. The atomizer is used to quantitative tests in an air-water cold system in combination with a particle dynamics analyzer (PDA). Linearized instability sheet atomization (LISA) model is employed to simulate the water atomization process. The effects of the distance from the nozzle outlet on the droplet size and velocity distribution in the downward spray are studied. Predictions of droplet diameters, trajectories, and velocities are made and they are compared with relevant experimental results; the predictions and results are found to be in good agreement.

Simulation and experimental validation of a methanol burner

This paper presents a computational fluid dynamics model of a methanol burner. Special emphasis was placed on the study of the liquid atomization and combustion process. Linearized Instability Sheet Atomization (LISA model) was employed to simulate the fuel atomization process. Predictions of droplet diameters, droplet trajectories, temperatures and gas concentrations are presented and compared with an experimental database presented by Widmann and Presser in their work a benchmark experimental database for multiphase combustion model input and validation. The predicted and simulated data were found to be in good agreement, however some discrepancies in the amount of unburned species were found probably related with the mechanism of combustion employed.

Impingement of hollow cone spray on hot porous medium

To have a good understanding of the formation of homogenous mixture in a porous medium engine, the interaction between hollow cone spray and hot porous medium was studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, heat transfer model and linearized instability sheet atomization (LISA) model to simulate the hollow cone spray. The reasonability of the impingement model and heat transfer model was validated. With a simple model to describe the structure of the porous medium, the interaction between hollow cone spray and hot porous medium was simulated under different ambient pressures and spray cone angles. Computational results show that the fuel spray could be divided into smaller ones, which provides conditions for the quick evaporation of fuel droplets and the mixing of fuel vapor with air. Differences in ambient pressure and spray cone angle affect the distribution of droplets in the porous medium.

Numerical modeling of hollow-cone fuel atomization, vaporization and wall impingement processes under high ambient temperatures

In the following paper, a numerical study of the atomization, vaporization and wall impingement processes of hollow-cone fuel spray from high-pressure swirl injectors under various ambient temperature conditions was carried out. Also, the availability of applied models and the effect of ambient temperature on spray characteristics is discussed. The Linearized Instability Sheet Atomization (LISA) model combined with the Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model, the improved Abramzon model and the Gosman model are used to calculate the atomization, vaporization and wall impingement processes of hollow-cone fuel spray, respectively. Spray models are implemented with the modified KIVA code. The calculation results of the spray characteristics under two ambient temperatures, including spray tip penetration, spray structure and radial distance after spray-wall impingement are compared to the experimental results obtained by the Laser Induced Exciplex Fluorescence (LIEF) technique. The droplet size distribution, ambient gas velocity field, vapor phase distribution and fuel film mass generated by spray-wall impingement, measurements which are generally difficult to obtain by experimental methods, are also calculated and discussed. Quantitative discussions on the effect of the ambient temperature on the spray development process are conducted. It is shown that the applied models are applicable even in the high ambient temperature condition.

Numerical investigation of the effects of fuel spray type on the interaction of fuel spray and hot porous medium

The interaction between two types of fuel spray and a hot porous medium is studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, a heat transfer model and a linearized instability sheet atomization (LISA) model to model the hollow cone spray. An evaporating fuel spray impingement on a hot plane surface was simulated under conditions of experiments performed by Senda to validate the reasonability of the KIVA-3V code. The numerical results conform well with experimental data for spray radius in the liquid and the vapor phases. Computational results on the interaction of two types of the fuel spray and the hot porous medium show that the fuel spray can be split, which provides conditions for quick evaporation of fuel droplets and mixing of fuel vapor with air. The possibility of fuel droplets from hollow cone spray crossing the porous medium reduces compared with that from solid cone spray, with the same initial kinetic energy of fuel droplets in both injection types.

Development and validation of a new hybrid break-up model for the modelling of hollow-cone fuel spray

In the present study, a numerical study and an experimental study on the break-up process of a hollow-cone fuel spray were performed. This was done to develop a new hybrid break-up model and to validate this model under various ambient pressure conditions. The new hybrid break-up model was composed of the linearized instability sheet atomization (LISA) model for the primary break-up and the aerodynamically progressed Taylor analogy break-up (APTAB) model, with consideration for the deformed droplet shape, for the secondary break-up. The APTAB model was used instead of the Taylor analogy break-up (TAB) model used in the previous hybrid break-up model (the LISA—TAB model). The hybrid break-up models were implemented in modified KIVA code. The calculated results of the spray characteristics, such as the spray tip penetration, spray width, Sauter mean diameter, and droplet velocity, by means of the LISA—APTAB model were compared with the calculated results via the LISA—TAB model and the experimental results found with the laser-induced exciplex fluorescence technique and the phase Doppler anemometry (PDA) system. The calculations and the experiment were performed under ambient pressures of 0.1 MPa and 0.5 MPa and an ambient temperature of 293 K. It was found that the calculated results from the LISA—APTAB model showed good agreement with the experimental results. The discrepancies between the calculated results and the experimental results in spray characteristics were reduced by a considerable margin by adopting the APTAB model instead of the TAB model for the secondary break-up process.

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 x2 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.

벽면 캐비티 각에 따른 GDI 분무의 벽 충돌 과정에 대한 수치적 연구

A spray-wall impingement process of a hollow-cone fuel spray from the high-pressure swirl injector in the Gasoline Direct Injection (GDI) engine were experimented and calculated at various wall geometries. The Linearized Instability Sheet Atomization (LISA) & the Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model and the Gosman model were applied to model the breakup and the wall impingement process of the hollow-cone fuel spray. The numerical modelings were implemented in the modified KIVA code. The calculation results of spray characteristics, such as a spray development process and a radial distance after wall impingement, compared with the experimental results by the Laser Induced Exciplex Fluorescence (LIEF) technique. The droplet size distribution and the ambient gas velocity field, which are generally difficult to obtain by the experimental methods, were also calculated and discussed. It was found that the radial distance after wall impingement and Sauter Mean Diameter (SMD) decreased with increasing a cavity angle.

Numerical simulation about interaction between pressure swirl spray and hot porous medium

To gain a deep understanding of the process of the fuel/air mixture formation and the role of the PM (porous medium) in mixture homogenization and combustion in a PM engine, the interaction of a pressure swirl spray and a hot porous medium was investigated computationally by using the modified KIVA-3V code in which an improved spray/hot wall interaction model was incorporated. The improved spray/hot wall interaction model fits into the regime above the Leidenfrost temperature, determines the properties of post-impingement fuel droplets and the quantity of heat transfer between the fuel droplets and a hot surface. An evaporating fuel spray impingement on a hot plane surface was simulated for validating the reasonability of the improved spray/hot wall interaction model. Numerical results compared well with experimental data for spray radius in the liquid and vapor phases. The linearized instability sheet atomization (LISA) model has been used to describe the atomization and breakup processes of the spray from the pressure swirl atomizers. The structure of a hot porous medium with porosity of 0.88 was established using a simple model. The injection, movement and vaporization of the fuel droplets inside the PM and their impingement on the block edges was computed. Consequently, the spatial distribution and time evolution of the temperature and fuel concentration inside the PM were obtained. The influences of the operating parameters, including ambient pressure and spray cone angle, on the characteristics of the fuel spray and mixture formation were discussed based on the numerical simulations. The basic aspects of the interaction between the pressure swirl spray and the hot porous medium have been revealed by the computational results.

분위기 조건에 따른 GDI 엔진용 인젝터의 분무거동 및 증발특성에 대한 수치적 해석

The purpose of this study is to improve the prediction ability of the atomization and vaporization processes of GDI spray. Several models have been introduced and compared. The atomization process was modeled using hybrid breakup model that is composed of Linearized Instability Sheet Atomization (LISA) model and Aerodynamically Progressed TAB (APTAB) model. The vaporization process was modeled using Spalding model and Abramzon ＆ Sirignano model. Exciplex fluorescence method was used for comparing calculated with experimental results. The experiment and computation were performed at the ambient pressure of 0.1 MPa, 0.5 MPa and 1.0 MPa and the ambient temperature of 293k and 473k. Comparison of calculated and experimental spray characteristics was carried out and the calculated results of GDI spray showed good agreement with experimental results.