Spray Formation Process Research Articles

Visualisation Testing of the Vertex Angle of the Spray Formed by Injected Diesel–Ethanol Fuel Blends

The internal combustion engine continues to be the main source of power in various modes of transport and industrial machines. This is due to its numerous advantages, such as easy adaptability, high efficiency, reliability and low fuel consumption. Despite these beneficial qualities of internal combustion engines, growing concerns are related to their negative environmental impacts. As a result, environmental protection has become a major factor determining advancements in the automotive industry in recent years, with the search for alternative fuels being one of the priorities in research and development activities. Among these, fuels of plant origin, mainly alcohols, are attracting a lot of attention due to their high oxygen content (around 35%). These fuels differ from diesel oil, for instance, in kinematic viscosity and density, which can affect the formation of the fuel spray and, consequently, the proper functioning of the compression–ignition engine, as well as the performance and purity of the exhaust gases emitted into the environment. The process of spray formation in direct injection compression–ignition engines is extremely complicated and requires detailed analysis of the fast-changing variables. This explains the need for using complicated research equipment enabling visualisation tests and making it possible to gain a more accurate understanding of the processes that take place. The present article aims to present the methodology for alternative fuel visualisation tests. To achieve this purpose, sprays formed by diesel–ethanol blends were recorded. A visualisation chamber and a high-speed camera were used for this purpose. The acquired video provided the material for the analysis of the changes in the vertex angle of the spray formed by the fuel blends. The test was carried out under reproducible conditions in line with the test methodology. The shape of the fuel spray is impacted by an increase in the proportional content of ethanol in the diesel and dodecanol blend. Based on the present findings, it is possible to note that the values of the vertex angle in the spray produced by the diesel–ethanol blend with the addition of dodecanol are most similar to those produced by diesel oil at an injection pressure of 100 MPa. The proposed methodology enables an analysis of the injection process based on the spray macrostructure parameters, and it can be applied in the testing of alternative fuels.

EFFECT OF FUEL TYPES AND INJECTION CONDITIONS ON SPRAY FORMATION AND GAS ENTRAINMENT PROCESSES IN DIESEL ENGINE

Due to its higher oxygen content, biodiesel fuel could play a vital role in the achievement of emission control in the heavy-duty transportation sector. Waste cooking oil (WCO) obtained from various sources such as the food industry, restaurants, and sewers could provide sustainable means of producing low-carbon fuel such as biodiesel. In this research, WCO biodiesel and conventional diesel fuels were characterized fundamentally in terms of their spray and gas entrainment qualities under diesel-like engine conditions using laser-induced fluorescence and particle image velocimetry (LIF-PIV). The impact of fuel injection parameters such as injection pressure and nozzle diameter on the fuel's spray and gas entrainment characteristics were investigated. Furthermore, an empirical equation was used to determine the droplet sizes of the sprays at different injection conditions. For both fuels, spray breakup and atomization were enhanced with the droplet size decreasing as injection pressure increased from 100 to 300 MPa and as nozzle size decreased from 0.16 to 0.08 mm. As a result of higher viscosity and surface tension, it was observed that WCO biodiesel produced longer spray penetration and narrower spray angle than diesel fuel. Furthermore, the quantity of gas entrained by WCO biodiesel spray was lower. As a result of an increase in the surface area, the percentage of gas entrained at the side periphery of the spray increased as time proceeded while the percentage of gas entrained via the spray tip decreased. The combined effect of ultra-high injection pressure of 300 MPa with a smaller nozzle hole diameter of 0.08 mm was observed to enhance gas entrainment processes.

Droplet impact dynamics on a flexible superhydrophobic cantilever wire mesh

Droplet impact on fixed permeable surfaces has many applications, including spray formation, coating deposition, and filtration processes. The present research studies the droplet and beam dynamics during the water droplet impact on the flexible superhydrophobic cantilever mesh, and the results are compared with the impact on a fixed-fixed superhydrophobic mesh. The effects of beam flexibility (droplet impact point), mesh opening size, and impact velocity on the rebound behavior of droplets, spreading diameter, contact time, beam deflection, and frequency were investigated. Although the contact time is reduced compared to the rigid surface, the well-known pancake rebound is not observed anymore on the cantilever beam. Therefore, the contact time reduction is not as pronounced as the fixed mesh for the cantilever beam. The spreading time and maximum spreading diameter decreased as the impact distance from the fixed point increased due to the reduced transmitted energy to the beam. However, the retraction time is affected by both beam dynamics and liquid penetration. Therefore, the shortest contact time depends not only on the oscillation and frequency of the beam and droplet but also on the liquid penetration. Moreover, the results prove that by defining an appropriate maximum spreading ratio, it becomes independent of the impact point. Finally, the beam deflection and frequency, in addition to the maximum spreading diameter of the droplet are modeled theoretically.

Numerical investigation of the effect of altitude on diesel engine combustion and soot emissions

It is increasing concerned that the plateau environment will potentially increase fuel consumption in engines. Despite this, the current state of research on high altitude engines is still inadequate in providing sufficient and detailed information to counteract the decrease in engine efficiency. In addition, one of the novelty of this study was that the investigated altitudes is up to 4500 m, of which the previous studies was limited. Therefore, this study aims to investigate the effect of altitude on in-cylinder spray, combustion, and soot formation processes in diesel engines. A calibrated three-dimensional (3D) computational fluid dynamics (CFD) model of a single-cylinder, four-strokes, direct injection (DI) compression ignition, intake boost research diesel engine is established. The numerical CFD model used in this study has been validated through comparison with experimental data. It effectively investigates the in-cylinder activities and provides insights into the causes behind combustion and soot emission deterioration. The simulation is operated at altitudes of 0, 1500, 3000, 4500 m with corresponding intake pressure. It has been observed that engine performance and soot emissions deteriorate as altitude increases, and a sharp drop occurs when the altitude exceeds 3000 m, which can be attributed to the dramatic decline in combustion efficiency. The extended spray leads to a decrease in air utilization, which ultimately results in a sudden drop in combustion efficiency at altitudes above 3000 m. Overall, this study has identified that the extended penetration of the spray, caused by reduced pressure and air density, leads to poor air utilization, resulting in decreased performance and increased emissions. Hence, it is recommended that optimization of the combustion chamber geometry and injection strategies of diesel engines operating at high altitudes be undertaken to improve air utilization and combustion quality. This will serve as an avenue for further research in the future.

Probabilistic derivation of droplet velocity using quadrature method of moments

Abstract Accurately prediction of dispersion and polydispersity of droplet flow is not a trivial task due to the complex behavior of the droplet size distribution (DSD) and the strong state of the instantaneous velocity of a droplet on the shape and size of the droplet. Describing the distribution of sizes and velocities of droplets initially formed in sprays is an essential piece of information needed in spray modeling, which is used to define the initial state of the spray droplets in the downstream two-phase flow fields’ predictive computations. The predictive model for the droplet size and velocity distributions in sprays is formulated as the droplet’s velocity magnitude has a power–law relationship with the droplet in this study. The present model incorporates the deterministic and stochastic aspects of the spray formation process. The quadrature method of moments (QMOM) is applied to solve numerically the transport equations of the probability density function coupled with conserved source terms incompressible Navier-Stokes equations for the liquid phase. The sub-models are connected by different source terms signifying the liquid-gas interaction. Equations of transport for spray moments are derived from DSD, and closure is attained using a gamma distribution. The integer spray moments concerning the volume are used to construct the continuous distribution of QMOM. In contrast, the velocity moments are used to determine the droplet velocity as a constant function of the droplet diameter. The model is first applied to simulate a diesel spray tip penetration under nonreactive conditions with different droplet velocity profiles to validate the approach with experimental data. An additional case of a liquid nitrogen spray is applied to show the gamma distribution’s ability to describe spray drop size distribution. The model generally predicts reasonable agreement with the experimental for both cases.

Combustion Instabilities and its Control Techniques for Liquid Propellant Rocket Engine

It is a great challenge for us to understand and to predict the concept of liquid propellant rocket engines combustion instability due to high complex turbulent combustion process. Traditional methods have been adopted to eliminate the combustion instabilities which will increase system damping. Such methods usually suffer deficiencies with lack of study on fundamental mechanism. Difficulties have been faced during the process of various phenomena such include spray formation process, turbulent multiphase flow conditions, hydrodynamics of injection and transport characteristics of individual droplets. The ultimate aim of every engine design is to prevent occurrence of this combustion instability and to maintain reliable operation during entire span of the combustion process. This article is focused on occurrence of various type of combustion instabilities in liquid propellant rocket engine and its preventing methods in detail.

Resolving the initial spray structure of fire sprinklers with a volume-of-fluid modeling

The initial spray formation process of commercial fire sprinklers was investigated with a Large-eddy simulation and a Volume-of-Fluid model. The water-supply flow rate was set to 80 L/min corresponding to the minimum required flow rate in South Korea. From the study of grid dependency, a mesh size of 62.5 μm was adopted. Using this size of the mesh, unstable wave growth on the surface of the liquid sheet was captured, which corresponds to 1/16 the size of a sprinkler droplet that was derived in a previous study to be 1 mm. Sprinkler spray consisted of horizontal sheets generated by tines and vertical sheets generated by slots. Ligaments were produced by vortices on the air-water interface and droplets were generated by both longitudinal and lateral stretching. The flow rate of the tine section was larger than that of the slot section due to the large section angle. The water at the tine section was delivered to neighboring slot sections as flowing downstream. A formula for the sheet thickness was calibrated with measured mass outflow, which showed a more accurate value than the original formula driven by the mass conservation for the plate.

Analysis of Wall impingement Spray and Film Formation Process of Direct Injection SI Engines under Low Temperature Conditions

Analysis of Wall impingement Spray and Film Formation Process of Direct Injection SI Engines under Low Temperature Conditions

Effect of water content in ethanol on spray formation at subcooled and flash-boiling conditions

Direct-injection spark-ignition engines can be more sensitive to fuel type as the time available for spray formation and mixing is rather limited. The challenge is further complicated by fuel stock which includes a significant bio-derived component in some markets to manage fuel sustainability. The thermophysical properties of bio-components like ethanol differ markedly from typical hydrocarbons found in gasoline like iso-octane. Moreover, the production of anhydrous ethanol fuel involves separating water and ethanol by distillation and dehydration in an energy intensive process. This study presents results from an optical investigation into the spray formation process of hydrous ethanol fuels with 4–15% water content per volume in direct comparison to anhydrous ethanol and iso-octane. Injection tests were carried out with 20–110°C fuel temperature at 1.0 bar and 0.5 bar gas pressure to mimic thermodynamic conditions of cold-start and fully-warm engine at low-load and wide-open-throttle operation. High-speed spray imaging was conducted along with droplet sizing by phase Doppler anemometry. The thermophysical properties of all fuels, including vapour pressure, density, viscosity and surface tension, as well as distillation curves, were obtained over a range of temperatures and the respective Reynolds, Weber and Ohnesorge numbers were considered in the analysis. At 20°C iso-octane and anhydrous ethanol exhibited similar spray plume penetration, whilst increasing water content in ethanol reduced spray penetration. At higher temperatures up to 90°C, anhydrous ethanol showed lower penetration than iso-octane whilst the hydrous fuels still exhibited lower penetration than anhydrous ethanol in sequence of increasing water content. At 110°C, the ethanol fuels showed signs of plume merging and spray collapse, particularly at 0.5 bar gas pressure, with clear differences from iso-octane. The degree of plume merging and collapse was stronger with increased water content. The cone angle for the hydrous fuels was higher than that of pure ethanol, with the 4% water content ethanol that was close to the azeotropic point showing wider cone angle at temperatures higher than 20°C, being distinctly higher at 90°C. Iso-octane had consistently smaller droplet Sauter mean diameter than the ethanol fuels. As the percentage of water content in ethanol increased there was an increase in droplet sizes at all conditions.

Spray development of iso-octane, ethanol, hydrous ethanol and water from a multi-hole injector under ultra cold fuel temperature conditions

Multi-hole injectors for direct-injection spark-ignition engines offer atomisation benefits and flexibility in fuel targeting by selection of the number and orientation of the nozzle’s holes. However, the spray formation process from multi-hole injectors has been mostly studied for hot fuel conditions and no quantitative data really exist with fuel temperatures representative of engine operation at cold-start. The challenge is further complicated by the predicted fuel stock which will include a significant bio-derived component presenting the requirement to manage fuel sustainability. The thermophysical properties of bio-components like ethanol differ markedly from typical hydrocarbons found in gasoline like iso-octane. Moreover, the production of anhydrous ethanol fuel involves separating water and ethanol by way of distillation and dehydration in an energy intensive process. This work presents results from an optical investigation into the effect of atomisation for iso-octane, anhydrous ethanol, hydrous ethanol with 10% water content per volume and water. Tests were first carried out at ambient conditions of 20 °C, 1 bar with 150 bar injection pressure using high-speed spray imaging. Then the fuel temperature was lowered to −5 °C, −10 °C and −15 °C to focus on spray formation analysis at realistic cold-start engine conditions. Droplet sizing was also conducted by Phase Doppler Anemometry (PDA). The thermophysical properties of all fuels, including vapour pressure, density, viscosity and surface tension, as well as distillation curves, were obtained over a range of temperatures, and the Reynolds, Weber and Ohnesorge numbers were considered in the analysis. The results revealed the degree of suppression of atomisation for each type of fuel at cold temperatures and effects on spray penetration and cone angle, with ethanol fuels exhibiting the strongest effect in the form of longer initial delay out of the nozzle and shorter penetration.

Influence of nozzle geometry on spray and combustion characteristics related to large two-stroke engine fuel injection systems

As emission regulations for large two-stroke marine Diesel engines increase as well, the manufacturers face similar problems as small-sized engine builders. The fuel injection, spray formation and subsequent combustion process remain among the main drivers for emissions of direct-injection, compression-ignition internal combustion engines. Since the fuel injection nozzle design of large two-stroke marine Diesel engines differs significantly, not only in size but especially regarding their non-symmetricity and eccentrical orifice arrangement, compared with four-stroke engines, the bulk of research available related to this topic is very limited.To further deepen the understanding of how in-nozzle cavitation flow during the fuel injection process affects the combustion behaviour in large two-stroke marine Diesel engines, transparent nozzle geometries have been used to link the cavitation phenomena with spray and combustion characteristics. A total of six single-orifice nozzles based on the original five-orifice nozzle design of large two-stroke marine Diesel fuel injectors, with and without hydro-erosive grinding, have been experimentally investigated under realistic engine conditions using highspeed optical measurement techniques and a unique constant-volume spray chamber that geometrically represents a combustion chamber of a large two-stroke marine Diesel engine at top dead centre.The spray morphology and combustion results reveal significant differences between the non- and hydro-erosive ground nozzle geometries. While the standard and angled nozzle versions remain similar, the eccentrical nozzle with its distinctive in-nozzle swirl cavitation pattern behaves differently, leading to a very reliable start of ignition behaviour and extreme wide spray angle.

Investigation of the spray formation and breakup process in an open-end swirl injector.

The spray formation and breakup process in an open-end swirl injector were studied through experiments and numerical simulations. A high-speed shadowgraph system and a high-speed backlight system were adopted to record the spray. Volume of fluid was used as the interface tracking method to capture the evolution process. The filling process of the liquid film inside the injector was captured. The air core formation process as observed in the experiments differed from that depicted by the numerical simulation results. The results revealed that the spray pattern of the cross-section at the tangential inlets also varied during the filling process. The evolution of the holes on the liquid film and ligaments was observed. It was determined that the liquid sheet repeatedly exhibited thinning, instability, shedding, breakup, and coalescence in the spray formation and breakup process. The spray pattern underwent the distorted pencil stage, onion stage, tulip stage, and fully developed stage with the increased injection pressure drop. The formation process of the open-end swirl injector also underwent these four stages under an injection pressure drop of 0.5 MPa.

Spray droplet size distribution and droplet velocity measurements in a firing optical engine

Macroscopic spray characteristics of a fuel injection system in an internal combustion (IC) engine have a direct impact on engine performance, emissions, and combustion characteristics. Nonintrusive in-cylinder measurements provide insights into the spray formation process for greater understanding of fuel-air mixing and combustion processes in an IC engine. In this paper, there are two parts: (a) procedure and methodology to configure the Artium phase Doppler interferometer (PDI) for in situ measurements through a cylindrical window and (b) comparative macroscopic spray characteristics in a firing Gasoline Direct Injection (GDI) optical engine to a constant volume spray chamber (CVSC) for spray droplet size-velocity distributions. Binned average velocity and average Sauter mean diameter of spray droplets in a firing engine were compared with that of a CVSC. Probability density function of droplet diameters in the CVSC under ambient conditions and in the engine combustion chamber provides an insight into the comparative droplet size distributions and droplet dynamics. Discussion on challenges encountered during PDI measurements in the firing engine environment, safety protocols, and tools required is also included. In addition, shadowgraphy images have been used to discuss the details on spray boundaries and spray evolution. The droplet size distribution inside the engine combustion chamber was found to be significantly different from the one observed in the CVSC. An engine simulation model can be developed/validated by using the data reported in this manuscript for attaining superior accuracy in the model. This paper describes the comparisons of the spray droplet size and velocity distributions in a CVSC and in situ for a working GDI engine. Maximum spray droplet velocity components (Vx, Vy) under engine combustion chamber conditions were 29.8 m/s, 14.2 m/s whereas the corresponding velocities in the CVSC under ambient conditions they were 78.41 m/s, 23.92 m/s, respectively, showing a large difference between the traditional measurements in the CVSC simulating engine conditions, and actual firing engine conditions. This study also reports the very first attempt in the open literature to measure spray droplet size and velocity distribution measurements in a firing IC engine.

N-Hexane injection into high-temperature and high-pressure environments

In this study, the process of n-hexane spray formation was investigated under a wide range of environmental conditions. The main aim of this research was to determine whether the global and visual properties of n-hexane spray change when the back pressure exceeds the critical pressure of the injected liquid. For this purpose, the liquid length and the boundary profile between the spray and surrounding air obtained by high-speed imaging of the Mie scattering signal were used. A major advantage of this work is that besides measuring global spray parameters, it provides quantitative analysis of the visual properties of the spray images; thus, the image analysis is not limited to qualitative visual impression. The results obtained in this study showed no step change in liquid length in terms of exceeding the critical parameters. Although qualitatively the boundary between the injected liquid and the surrounding gas seemed to become smoother in high-pressure and high-temperature conditions, the qualitative analysis did not support this observation.Graphic abstract

Highly resolved Eulerian simulations of fuel spray transients in single and multi-hole injectors: Nozzle flow and near-exit dynamics

In high pressure fuel injectors, needle opening and closing transients cause complex off-design fluid dynamics behaviors that profoundly impact the spray and mixture formation processes. These dynamics are completely different from what is known to occur in steady state conditions.In this study, diesel spray transients have been investigated in single-hole and 3-hole nozzles, encompassing internal and external nozzle flow and including needle motion, performing highly resolved (2.5 μm) computational fluid dynamics (CFD) simulations. We focused on end-of-injection (EOI) and start-of-injection (SOI) processes, in order to provide insights in to the physics. The liquid fuel, vapor and gas species are modeled with a single-fluid multiphase mixture approach, with diffuse interface, and with large eddy simulations (LES) of the turbulence. Occurrence of phase change due to cavitation is accounted for, and the spray dispersion is described with a turbulent dispersion model. Detailed needle motion data and orifice internal surface are available from x-ray synchrotron source measurements carried out at Argonne National Laboratory, and shared through the Engine Combustion Network (ECN) community. Simulations are compared against x-ray phase contrast imaging and radiography of the internal and near-exit flow, in addition to optical microscopy data of the near-exit sprays.Simulation results are found to agree well with available experimental data, and are able to realistically capture local and global features. The simulations allow to gain insight into the physics of gas ingestion and dribbles at EOI, for different hole diameters, operating conditions and number of holes. At SOI, timing of liquid appearance out of the injector and spray tip penetration are adequately predicted, by using the EOI flow field as in-nozzle initialization, and by prescribing the measured tip needle displacement with an informed effective valve opening point inferred from the x-ray observations. Lastly, the variation of spreading angle over time is also discussed in detail for the multi-hole case, including hole-to-hole variations. Due to real geometry features and asymmetric needle motion with eccentric components, it is found that the three holes exhibit swirling flows of increasing intensity as the lift decreases, causing the near cone angle to open and spread, in a quasi-hollow cone structure. These features are not observed in axial single-hole injectors because of their relative simplicity and intrinsic symmetry.

Spatio-temporal effect of the breakdown zone in the laser-initiated ignition of atomized ethyl alcohol-air mixture

Laser initiated ignition would play a vital role in future gas turbine combustors. Two lasers of 270 μJ and 50 mJ pulse energy are used to study the laser-induced spark ignition of atomized ethyl alcohol-air mixture. With the low-energy pulse of 270 μJ energy, no display of ignition is observed even though it fulfills the threshold conditions to create breakdown. However, with the high-energy pulse of 50 mJ energy, ignition is observed if the plasma kernel was following certain conditions after the occurrence of the breakdown. It is observed that breakdown created by the low-energy pulse was unable to ignite the atomized ethanol-air mixture because the lifetime of the plasma kernel was very small (in microseconds). While performing the study with high-energy pulse, it is observed that the breakdown becomes a sufficient condition for ignition only when the lifetime of the kernel is couple of milliseconds. Additionally, the spatial location of the laser spark is found to play a vital role in successful ignition of the mixture. This work also discusses the spray formation process with its effect on ignition and the role of the third lobe on rapid development of the plasma kernel. The process of laser energy deposition to full scale combustion is categorized into three events. Finally, based on the experimental observations, this work has proposed some favourable conditions for initiating ignition with a laser spark. Knowledge of the proposed conditions can play a vital role for designing a practical laser ignition system.

What Determines the Drop Size in Sprays?

In many instances, sprays are formed from the breakup of liquid jets or sheets. We investigate the different parameters that determine the characteristic drop size in the breakup of sheets. We vary both the spraying parameters, such as the pressure and geometry of the nozzle, and the fluid parameters, such as viscosity and surface tension. The combined results show that the drop size is determined by a competition between fluid inertia and surface tension, which allows for the prediction of the drop size from the Weber number and geometry of the nozzle. Once rescaled with the average drop size, the size distribution is found to be described by a compound gamma distribution with two parameters, n and m, with the former setting the ligament corrugation and the latter the width of the ligament size distribution. Fit values for m indicate that nozzles of a conical type produce ligaments of almost equal size, while the flat fan nozzles produce broader distributed ligament sizes. Values for n show that, for all nozzles, ligaments are very corrugated, which is not unexpected for such spray formation processes. By using high-speed photography of the sprays, the parameters m and n can be directly measured and, indeed, govern the drop-size distribution.

Computational assessment of temperature variations through calibrated orifices subjected to high pressure drops: Application to diesel injection nozzles

This paper conducts an investigation on the temperature variations experienced by the fuel when it expands through the calibrated orifices of a commercial diesel injector. Experimental results of the temperature change across a calibrated orifice upon expansion, extracted from a previous work, are compared to the temperature predicted by computational fluid dynamic simulations under the assumption of adiabatic flow, with no heat transfer to the surroundings. The comparison points out that the simulations are able to predict the thermal effects taking place inside the orifice. Once the model is validated, the flow morphology is analyzed to explain the trends observed in the fuel temperature change across the orifice depending on the operating conditions. Two opposed effects take place inside the orifice: on the one hand, the flow is cooled in the orifice core due to depressurization; on the other hand, the fuel is importantly heated near the walls due to viscous friction. As expected, the net effect on the outlet temperature mainly depends on the orifice discharge coefficient, governed by the orifice geometry and the flow regime (Reynolds number) induced by the injection conditions. Next, the analysis is extended to a diesel nozzle, considering that the higher pressure drops achieved in it are expected to induce even more important thermal effects. The two opposed effects also take place inside the orifice. Even though their net effect is similar, the separate effect of each phenomenon is greater, leading to differences that could be relevant for the atomization and spray formation processes. Additionally, the flow pattern shows a non-uniform distribution of the flow inside the nozzle influencing the results from the thermal point of view.

Detailed SGS atomization model and its implementation to two-phase flow LES

A novel turbulent atomization model, which is physically closed itself and free of case-by-case parameter tuning using experimental data, has been formulated and demonstrated in the framework of turbulent spray combustion large-eddy simulation (LES). Based on our accumulated research findings that elementary droplet/ligament generation is a deterministic phenomenon, not something random as considered in the conventional understanding, the model describes two dominant modes of turbulent atomization, i.e. the turbulent resonant mode and the Rayleigh–Taylor (RT) mode, in a physically straightforward manner. Extending the baseline theory proposed in Umemura (2016), to a hybrid turbulent spray LES formulation which includes both an Eulerian liquid jet core and Lagrangian droplets, the subgrid-scale (SGS) atomization characteristics are completely detailed in this study. Using the LES-resolved turbulent Weber and Bond numbers on the liquid core surface, the atomization mode and the SGS atomization characteristics such as droplet size, number, ejection velocity and core regression velocity are all identified locally, and the information is transferred back to the LES code as input information. Test cases of Diesel fuel jets demonstrate that the present formulation well reproduces the turbulent spray behavior. Thanks to the obtained detailed data, the spray formation process can be tracked both temporally and spatially, from the initial head formation with edge atomization to the later core atomization and spray spreading. It is essentially featured that the present turbulent atomization model works well without ambiguous user input, contrary to the conventional way of spray simulation. This is a significant breakthrough to urge paradigm shift in spray simulation, from unclosed/unpredictable to closed/predictable, which enables drastic improvement in the accuracy of spray simulation and may exert a large impact on both research studies and industrial applications.

Internal flow characteristics in scaled pressure-swirl atomizer

Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, cooling, painting, food processing etc. Their spray characteristics are closely linked to the internal flow which predetermines the parameters of the liquid sheet formed at the discharge orifice. To achieve a better understanding of the spray formation process, the internal flow was characterised using Laser Doppler Anemometry (LDA) and high-speed imaging in a transparent model made of cast PMMA (Poly(methyl methacrylate)). The design of the transparent atomizer was derived from a pressure-swirl atomizer as used in a small gas turbine. Due to the small dimensions, it was manufactured in a scale of 10:1. It has modular concept and consists of three parts which were ground, polished and bolted together. The original kerosene-type jet A-1 fuel had to be replaced due to the necessity of a refractive index match. The new working liquid should also be colourless, non-aggressive to the PMMA and have the appropriate viscosity to achieve the same Reynolds number as in the original atomizer. Several liquids were chosen and tested to satisfy these requirements. P-Cymene was chosen as the suitable working liquid. The internal flow characteristics were consequently examined by LDA and high-speed camera using p-Cymene and Kerosene-type jet A-1 in comparative manner.