Airblast Atomizer Research Articles

Experimental investigation on swirling annular liquid film breakup characteristics of prefilming airblast atomizer

In order to further improve the understanding of the liquid film breakup characteristics of prefilming airblast atomizer, the effects of key operating parameters and structural parameters (swirl intensity, diameter and number of injection holes on pilot stage, length of pre-film lip and sleeve angle) on the liquid film pattern of prefilming airblast atomizer were investigated using the high-speed shadow method and the Otsu’s method. The mechanism of liquid film breakage was analyzed, the results show that, with the increase of fuel injection pressure, the spray morphology experiences “columnar-shaped”, “tulip-shaped” and “fully cone-shaped”. Meanwhile, the main fluctuation frequency of liquid film varies from 100.5 Hz in the “columnar-shaped” and “tulip-shaped” to 25.12 Hz in the “fully cone-shaped”. With increasing relative pressure drops of swirler, the film breakup length and film fluctuation frequency decrease, while the film fluctuation amplitude increases. An increase in inner-stage swirl intensities will lead to a reduction in the film breakup distance, while an increase in outer-stage swirl intensities will mainly lead to a larger spray angle. The increase of the diameter and number of injection holes and the length of pre-film lip leads to the rise of the liquid film breakup length, while the decrease of sleeve angle mainly leads to the rise of spray angle, which makes the liquid film more easily broken.

Effect of Methane on Combustion of Glycerol and Methanol Blends Using a Novel Swirl Burst Injector in a Model Dual-Fuel Gas Turbine Combustor

Glycerol, a byproduct of biodiesel, has moderate energy but high viscosity, making clean combustion challenging. Quickly evaporating fine fuel sprays mix well with air and burn cleanly and efficiently. Unlike conventional air-blast atomizers discharging a jet core/film, a newly developed swirl burst (SB) injector generates fine sprays at the injector’s immediate exit, even for high-viscosity fuels, without preheating, using a unique two-phase atomization mechanism. It thus resulted in ultra-clean combustion for glycerol/methanol (G/M) blends, with complete combustion for G/M of 50/50 ratios by heat release rate (HRR). Lower combustion efficiencies were observed for G/M 60/40 and 70/30, representing crude glycerol. Hence, this study investigates the effect of premixed methane amount from 0–3 kW, and the effect of atomizing gas to liquid mass ratio (ALR) on the dual-fuel combustion efficiency of G/M 60/40-methane in a 7-kW lab-scale swirl-stabilized gas turbine combustor to facilitate crude glycerol use. Results show that more methane and increased ALR cause varying flame lift-off height, length, and gas product temperature. Regardless, mainly lean-premixed combustion, near-zero CO and NOx emissions (≤2 ppm), and ~100% combustion efficiency are enabled for all the cases by SB atomization with the assistance of a small amount of methane.

Two approaches for constructing multivariate injection models for prefilming airblast atomizers

Two approaches for constructing multivariate injection models for prefilming airblast atomizers

An experimental investigation on role of turbulence modulation induced by thread structure in coaxial air blast atomization of a surfactant-laden jet

An experimental investigation on role of turbulence modulation induced by thread structure in coaxial air blast atomization of a surfactant-laden jet

Coaxial air blast atomization of a particulate gel suspension jet

Coaxial air blast atomization of a particulate gel suspension jet

Flame dynamics and oscillation characteristics based on statistical analysis in a combustor with prefilming and non-prefilming atomization

Suppressing thermoacoustic oscillations in low-emission combustors during their operation poses a major challenge. In this study, we report dynamic flame tests on combustors with prefilming (S1) and non-prefilming (S2) airblast atomizers. We used the image fast Fourier transform, proper orthogonal decomposition, dynamic mode decomposition, and continuous wavelet transform to obtain the spatial distribution of pulsations and spectral characteristics of the flames. The results reveal that the flames of S1 and S2 were significantly different. The combustor of S1 had a dome-attached flame confined to the primary combustion zone, while S2 had a lifted flame that filled the entire combustor. As the rate of airflow at the inlet increased, the flame of S1 exhibited oscillatory combustion, while the flame of S2 remained stable under all tested conditions, which was consistent with observations of its dynamic images. No characteristic peak was observed in the spectra of S2 under all operating conditions, and under rates of inlet airflow of 40 and 60 g/s for S1. However, pulsations in the chemiluminescence signals of the flame had a primary frequency of 116.4 Hz and secondary harmonic at 232.4 Hz at 80 g/s for S1. At 100 g/s, the S1 flame exhibited a primary frequency of 142.9 Hz, secondary harmonic at 285.4 Hz, and tertiary harmonic at 428.3 Hz. Minor adjustments to the geometry of the airblast atomizer can thus significantly alter the mode of spray–wall interactions and impact flame dynamics. Consequently, this study proposes a new control technique for instability suppression.

Air-Film Coupling in Prefilming Airblast Atomisers and the Implications for Subsequent Atomisation

Prefilming airblast atomisers are commonly used in gas turbine combustion system fuel injectors. As the film propagates across the prefilmer it interacts with the high velocity gas stream above it. In this paper a numerical investigation into this interaction is presented. A Coupled Level Set & Volume of Fluid method is used to simulate the development of the film along the KIT-ITS planar prefilmer (Gepperth et al., in: 23rd European conference on liquid atomization and spray systems (ILASS-Europe 2010), Brno, Czech Republic, September, 2010). Initial results showed the importance of correctly specifying the contact angle as too high a value leads to the formation of rivulets instead of a continuous film. An analysis of the film and air showed two-way coupling. The presence of the film increases the growth rate of the gas phase boundary layer, and the strength and size of the turbulent structures within it. Surface waves form in the film, initially driven by the turbulent fluctuations, but developing into transverse waves. These waves are shown to be independent, stochastic events instead of a periodic wave system. At the trailing edge of the prefilmer the increased turbulence level in the air, the variations in the film thickness and the associated change in fuel mass flow and momentum will have large implications for the atomisation process and subsequent fuel spray. These will also impact simulation of the atomisation, as the boundary condition complexity is much greater than commonly used, and the variations will require larger domains and longer simulation times to obtain fully converged atomisation statistics.

Investigation of Spray Characteristics for Detonability: A Study on Liquid Fuel Injector and Nozzle Design

Detonation engines are gaining prominence as next-generation propulsion systems that can significantly enhance the efficiency of existing engines. This study focuses on developing an injector utilizing liquid fuel and a gas oxidizer for application in detonation engines. In order to better understand the spray characteristics suitable for the pulse detonation engine (PDE) system, an injector was fabricated by varying the Venturi nozzle exit diameter ratio and the geometric features of the fuel injection hole. Analysis of high-speed camera images revealed that the Venturi nozzle exit diameter ratio plays a crucial role in determining the characteristics of air-assist or air-blast atomization. Under the conditions of an exit diameter ratio of Re/Ri = 1.0, the formation of a liquid film at the exit was observed, and it was identified that the film’s length is influenced by the geometric characteristics of the fuel injection hole. The effect of the fuel injection hole and Venturi nozzle exit diameter ratio on SMD was analyzed by using droplet diameter measurement. The derived empirical correlation indicates that the atomization mechanism varies depending on the Venturi nozzle exit diameter ratio, and it also affects the distribution of SMD. The characteristics of the proposed injector, its influence on SMD, and its velocity, provide essential groundwork and data for the design of detonation engines employing liquid fuel.

Near-field spray characteristics and steadiness of a novel twin-fluid injector with enhanced primary atomization

Near-field spray characteristics and steadiness of a novel twin-fluid injector with enhanced primary atomization

Air-blast atomization of a liquid film

Air-blast atomizers are extensively used for a variety of purposes. Due to its complexity, the atomization mechanism has not been elucidated. In this study, a mechanistic model is proposed to predict the droplet diameter distribution based on the atomization process of a planar liquid film with co-current gas flows, and its validity is examined by comparing the estimated and measured droplet diameters using high-speed image analysis and laser measurement. As a result, using high-speed imaging, we clarified that the bag film rupture is caused not by the turbulence of the gas flow but by the impact of floating droplets on the liquid film of the expanding bag when the film is thin enough. The average thickness of the liquid film at the bag breakup is of the order of micrometres and varies greatly, resulting in a dispersed distribution of droplet diameters. After the film ruptures, the bag film shrinks towards its transversal and vertical rims due to surface tension, forming large-diameter ligaments. During the contraction process of the bag film, tiny droplets of the order of micrometers are formed at the edge of the perforation. Finally, the remaining ligaments with large diameters fragment into large droplets with submillimetre diameters. The good agreement between the measured and predicted droplet diameter distributions validated the mechanistic model.

Dual-camera off-axis holographic particle tracking velocimetry: Development and application to air-blast swirl spray measurement

Dual-camera off-axis holographic particle tracking velocimetry: Development and application to air-blast swirl spray measurement

The Effect of Film Development on Primary Breakup in a Prefilming Airblast Atomizer

Abstract Liquid fueled gas turbines are likely to remain a dominant force in aviation propulsion for the foreseeable future, and therefore understanding the atomization process is key to meeting future emissions and performance legislation. To make experiments and simulations possible, simplified geometry and boundary conditions are often used, for example, simulations of primary atomization often use a fixed film height and velocity. This paper aims to quantify the effect of a fully developed unsteady film on the atomization process. A custom Coupled Level Set & Volume of Fluid (CLSVOF) solver with adaptive meshing built in OpenFOAM v9 is used. A simulation of the atomization process in the Karlsruhe Institute of Technology atomization experiment (Warncke et al., 2017, “Experimental and Numerical Investigation of the Primary Breakup of an Airblasted Liquid Sheet,” Int. J. Multiphase Flow, 91, pp. 208–224) is presented. A precursor simulation of the film development is used to provide accurate, temporally and spatially resolved inlet boundary conditions. These results are compared to previous CLSVOF simulations from Wetherell et al. (2020, “Coupled Level Set Volume of Fluid Simulations of Prefilming Airblast Atomization With Adaptive Meshing,” ASME Paper No. GT2020-14213)” using traditional boundary conditions. The unsteady film has doubled the modal ligament length and widened the distribution, and is now in better agreement with experimental measurements. A clear correlation in both time and space is observed between the film, atomization process, and spray. The sauter mean diameter (SMD) is significantly increased, again giving better agreement with the experiment. A discussion of extracting statistical descriptions of the spray is given, outlining the unfeasible computational cost required to converge droplet diameter distributions and other high order statistics for a case such as this.

A DETAILED NUMERICAL INVESTIGATION OF TWO-PHASE FLOWS INSIDE A PLANAR FLOW-BLURRING ATOMIZER

Flow-blurring atomization is an innovative twin-fluid atomization approach that has demonstrated superior effectiveness in producing fine sprays compared to traditional airblast atomization methods. In flow-blurring atomizers, the high-speed gas flow is directed perpendicular to the liquid jet. Under specific geometric and physical conditions, the gas penetrates back into the liquid nozzle, resulting in a highly unsteady bubbly two-phase mixing zone. Despite the remarkable atomization performance of flow-blurring atomizers, the underlying dynamics of the two-phase flows and breakup mechanisms within the liquid nozzle remain poorly understood, primarily due to the challenges in experimental measurements of flow details. In this study, detailed interface-resolved numerical simulations are conducted to investigate the two-phase flows generated by a planar flow-blurring atomizer. By varying key dimensionless parameters, including the dynamic-pressure ratio, density ratio, and Weber number, over wide ranges, we aim to comprehensively characterize their effects on the two-phase flow regimes and breakup dynamics.

Investigation into the Effect of H2-Enriched Conditions on the Structure and Stability of Flames in a Low-Swirl Combustor Derived from Aero-Engine Design

This study introduces an innovative approach involving the injection of hydrogen into a low-swirl, non-premixed flame, which operates with gaseous fuels derived from an air-blast atomizer designed for aero-engine applications. The aim is to characterize how hydrogen enrichment influences flame structures while maintaining a constant thermal output of 4.6 kW. Using high-speed chemiluminescence imaging, three fueling conditions were compared: the first involved pure methane/air, while the second and third conditions introduced varying levels of hydrogen to an air–methane mixture. The results reveal significant effects of hydrogen enrichment on flame characteristics, including a slightly shorter length and a wider angle attributed to heightened expansion within the Combustion Recirculation Zone. Moreover, the emission of UV light underwent considerable changes, resulting in a shifted luminosity zone and reduced variance. To delve deeper into the underlying mechanisms, the researchers employed Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD) analyses, showing coherent structures and energetic modes within the flames. Hydrogen enrichment led to the development of smaller structures near the nozzle exit, accompanied by longitudinal oscillations and vortex shedding phenomena. These findings contribute to an advanced understanding of hydrogen’s impact on flame characteristics, thereby propelling efforts toward improved flame stability. Additionally, these insights hold significance in the exploration of hydrogen as an alternative energy source with potential environmental benefits.

Design and Performance Evaluation of an Air-Blast Atomizer

Design and Performance Evaluation of an Air-Blast Atomizer

DEVELOPMENT OF SMART DISINFECTION MACHINE USING IOT TECHNOLOGY

In this study, the authors developed a smart, high power of disinfection machine using IoT technology. This disinfection machine generates super fine fog from H2O2 solution by utilizing pressure-swirl airblast atomizer. This machine sprays the H2O2 fog into the air inside the operating room in hospitals to disinfect and make the environment clean. The operation of the disinfection machine is totally remote controlled via mobile application using Bluetooh Low Energy (BLE) communication technology. All operating parameters are remotely, real time monitored and controlled. In addition, the machine operation history of are fully collected and stored both on a memory card in control circuit board and on cloud database. Furthermore, the heat generation from the integrated circuits (ICs) or chip and electronic components on the control printed circuit board (PCB) is also studied in order to prevent the overheating of the components which cause malfunction or instability of the machine. The results show that the temperature of all the electronic components on the control PCB during working is within the temperature allowance, and the disinfection machine works well.

Modeling Multivariate Spray Characteristics with Gaussian Mixture Models

With the increasing demand for efficient and accurate numerical simulations of spray combustion in jet engines, the necessity for robust models to enhance the capabilities of spray models has become imperative. Existing approaches often rely on ad hoc determinations or simplifications, resulting in information loss and potentially inaccurate predictions for critical spray characteristics, such as droplet diameters, velocities, and positions, especially under extreme operating conditions or temporal fluctuations. In this study, we introduce a novel approach to modeling multivariate spray characteristics using Gaussian mixture models (GMM). By applying this approach to spray data obtained from numerical simulations of the primary atomization in air-blast atomizers, we demonstrate that GMMs effectively capture the spray characteristics across a wide range of operating conditions. Importantly, our investigation reveals that GMMs can handle complex non-linear dependencies by increasing the number of components, thereby enabling the modeling of more complex spray statistics. This adaptability makes GMMs a versatile tool for accurately representing spray characteristics even under extreme operating conditions. The presented approach holds promise for enhancing the accuracy of spray combustion modeling, offering an improved injection model that accurately captures the underlying droplet distribution. Additionally, GMMs can serve as a foundation for constructing meta models, striking a balance between the efficiency of low-order approaches and the accuracy of high-fidelity simulations.

Investigation of Thermal Radiation, Atomization Air, and Fuel Temperature Effects on Liquid Fuel Combustion

Abstract The purpose of the present study is to investigate the effects of radiative heat transfer, atomization air temperature and mass flowrate, and fuel initial temperature on liquid diesel fuel (C16H34) combustion. Fuel is injected by an airblast atomizer inside a model cylindrical combustion chamber. Geometry of the airblast atomizer is modeled in detail so that its impacts on droplet breakup and flow formation are accurately considered. Evaporating fuel spray is simulated by the discrete phase model based on the Eulerian–Lagrangian approach. Turbulent viscosity is numerically computed by the realizable k–ɛ turbulence model while the discrete ordinates model and the steady flamelet model are applied for modeling the radiative heat transfer and combustion, respectively. NO species concentrations are achieved using post-processing. It turns out that neglecting thermal radiation in well-atomized spray combustion only affects high-temperature zones by increasing the axial temperature values of the mixture by almost 8%. Thermal radiation has an imperative effect on producing NO species. Without considering thermal radiation, axial NO concentration becomes almost doubled. Augmentation in mass flowrate and temperature values of atomization air enhances spray formation and combustion efficiency by increasing the evaporation rate. Changing the fuel temperature from 300 K to 325 K rises the total temperature at the end of the centerline of the model combustion chamber by 9.8%. It is shown that increasing the fuel’s initial temperature is not a suitable choice compared to enhancing the temperature and mass flowrate of the atomization air.

Effect of atomizer and cross-flows on liquid and gelled Jet A-1 fuel injection

The current study aims to experimentally investigate the effect of atomizer and cross-flow velocities on liquid and gelled Jet A-1 fuels. For gelled Jet A-1, Jet A-1 liquid, Thixatrol® ST and rectified xylene are the base fuel, gellant and solvent, respectively. Gelled Jet A-1 is prepared by adding 85% by weight of base fuel along with 7.5% by weight of gellant and solvent, each at optimum processing conditions. Atomization using a simple-plain-orifice atomizer is investigated to understand its effect on Jet A-1 gel fuel break-up without air cross-flow. Based on the investigation from qualitative flow visualization and quantitative analysis of Jet A-1 gel fuel break-up, a modified simple-plain-orifice atomizer called an internally impinging air-blast atomizer is made. Primary atomization using this new atomizer is studied to understand the break-up of liquid and gelled Jet A-1 gel fuels without any air cross-flow. Secondary atomization of liquid and gel fuel is investigated by transversely injecting fuel into different low-speed subsonic air cross-flow environments. Laser sheet Imaging (LSI) technique is used to capture spray images of both fuels. Break-up mechanisms of both liquid and gel fuels were observed, and the results were compared. Information on the cross-flow air mass flow rate effect on the liquid and gel spray is extracted by developing an algorithm in MATLAB using an image processing tool. Relative droplet size distribution of liquid and gel spray revealed their dependence on cross-flow air mass flow rate. Total droplet count of both liquid and gel fuel decreases significantly as the cross-flow Reynolds’ number increases. At higher cross-flow Reynolds’ number, gel droplets in the flow are observed to be more as compared to liquid fuel.

Air-blast atomization and ignition of a kerosene spray in hot vitiated crossflow

Air-blast atomization and ignition of a kerosene spray in hot vitiated crossflow