Spray Shape Research Articles

Effects of slit geometric parameters on spray characteristics of double-slit pintle injectors

Pintle injectors have garnered significant research attention in recent years, particularly for their applicability in reusable launch vehicles, owing to their wide thrust control range and excellent combustion stability. While research has explored the characteristics of pintle injectors in the context of developing these components for actual engine applications, studies focusing on the effects of design parameters on injector performance have been limited. This study investigated the effects of slit geometric parameters, specifically the blockage factor (BF) and slit area ratio (γ), on the spray characteristics of double-slit pintle injectors. Cold-flow tests were conducted using planar pintle injectors with water and ethanol as simulants. The spray angle and Sauter mean diameter (SMD) were measured using the shadowgraph technique, and the distribution of mass flow rate and mixture ratio was analyzed using a mechanical patternator. The experimental results revealed that two distinct streams were injected at different angles from each row of slits, resulting in a division of spray shape, SMD, and mass flow distribution into three regions based on the two streams. These spray angles, termed primary and secondary spray angles, were quantified as functions of the local momentum ratio, determined by BF and γ. To correlate the spray characteristics with combustion performance, mixing quality and a representative droplet size metric, the integral Sauter mean diameter (ID32), were presented. The study found that higher values of BF and γ corresponded to improved mixing quality.

Spray Characterization of Direct Hydrogen Injection as a Green Fuel with Lower Emissions

A viable green energy source for heavy industries and transportation is hydrogen. The internal combustion engine (ICE), when powered by hydrogen, offers an economical and adaptable way to quickly decarbonize the transportation industry. In general, two techniques are used to inject hydrogen into the ICE combustion chamber: port injection and direct injection. The present work examined direct injection technology, highlighting the need to understand and manage hydrogen mixing within an ICE’s combustion chamber. Before combusting hydrogen, it is critical to study its propagation and mixture behavior just immediately before burning. For this purpose, the DI-CHG.2 direct injector model by BorgWarner was used. This injector operated at 35 barG and 20 barG as maximum and minimum upstream pressures, respectively; a 5.8 g/s flow rate; and a maximum tip nozzle temperature of 250 °C. Experiments were performed using a high-pressure and high-temperature visualization vessel available at our facility. The combustion mixture prior to burning (spray) was visually controlled by the single-pass high-speed Schlieren technique. Images were used to study the spray penetration (S) and spray volume (V). Several parameters were considered to perform the experiments, such as the injection pressure (Pinj), chamber temperature (Tch), and the injection energizing time (Tinj). With pressure ratio and injection time being the parameters commonly used in jet characterization, the addition of temperature formed a more comprehensive group of parameters that should generally aid in the characterization of this type of gas jets as well as the understanding of the combined effect of the rate of injection on the overall outcome. It was observed that the increase in injection pressure (Pinj) increased the spray penetration depth and its calculated volume, as well as the amount of mass injected inside the chamber according to the ROI results; furthermore, it was also observed that with a pressure difference of 20 bar (the minimum required for the proper functioning of the injector used), cyclic variability increased. The variation in temperature inside the chamber had less of an impact on the spray shape and its penetration; instead, it determined the velocity at which the spray reached its maximum length. In addition, the injection energizing time had no effect on the spray penetration.

Breakup mode of continuous-type liquid-liquid pintle injector

A pintle injector is necessary for the reuse of a launch vehicle. Significant studies have been conducted on the breakup process in impinging or swirl type injectors. However, the breakup process in liquid-liquid pintle injectors from injection to the atomization of liquid films has rarely been investigated. Therefore, in this study, the breakup mode and process quantified characteristics of the pintle injector were investigated. The backlight imaging technique was applied to capture the spontaneous phenomenon, and a longitudinal section view of the spray on the pintle injector was obtained using the 2P-SLIPI technique. The breakup modes were classified into three categories based on the spray shape (hollow cone, fishbone, and branch). The atomization process was investigated with high-speed and SLIPI images in chronologicalorder. Schematics of the process were also prepared to understand the breakup mechanism. The dynamic characteristics, such as breakup frequency and peak amplitude, and static characteristic (breakup length) were investigated using the flow Weber number. Furthermore, the dynamic characteristics are dependent on the radial flow, and the static characteristics are influenced by the annular jet flow. This study will serve as a reference for the breakup mechanism and characteristics of a liquid-liquid pintle injector design.

Two-way Eulerian-Lagrangian coupling approach in GASFLOW code for containment spray modelling

Spray droplets are considered to have significant effects on the gas mixing and depressurization in the containment of nuclear power plants during hypothetical accident scenarios. The Eulerian-Lagrangian approach, which enables the two-way mass, momentum, and energy coupling of the continuous gas and the dispersed spray droplets, is promising to model the behaviours of spray droplets in 3D simulations of the full-scale containment. Two-way heat and mass transfer models have been developed in the 3D CFD code GASFLOW. The particle group method is applied in the Lagrangian approach to track the droplets. The ordinary differential equations which couple the local heat and mass exchanges between each droplet group and the surrounding gas mixtures have been solved using the Runge-Kutta method. The GASFLOW coupling this new approach is validated by TOSQAN water spray experiments, which demonstrate the good feasibility of implementing the approach. The analysis of the impact of the spray on containment atmosphere indicates that: 1) the droplet swarm entrains and mixes the surrounding gas, breaking up the gas stratification, with turbulent diffusion dominating momentum mixing in dead zones; 2) the thermal and mass exchanges between the spray droplet swarm and gas jointly determine the atmosphere depressurization, with the evaporation of the spray-formed film/sump on heat structures of great importance for the containment pressure development; and 3) these spray thermodynamic and dynamic effects highly depend on the droplet size distribution and the spray shape.

Three-dimensional simulation of a gas-centered swirl coaxial injector spray under pulsation conditions

Based on steady-state experiments, a three-dimensional (3D) simulation study under pulsation conditions was carried out. This was performed to study the effect of pulsation of the supply system on the atomization characteristics of a gas-centered swirl coaxial injector. The results indicated that the spray shape resembled a pagoda when the Klystron effect occurred. When the low-frequency pulsation (200 Hz) was applied to the liquid inlet, the peak of the exit pressure was close to the trough of the inlet mass flow rate. Meanwhile, the exit mass flow rate and pressure were approximately sinusoidal. There was no significant lag effect in the response of the exit mass flow rate to the inlet mass flow rate but with a small sawtooth-like oscillation. Increasing the amplitude of the liquid inlet disturbance amplified the exit mass flow rate fluctuation, which was greater than the set amplitude of the inlet pulsation. The dominant frequency of the injector exit mass flow rate and pressure variation was significantly less than the inlet pulsation frequency when the frequency of the liquid inlet pulsation was increased to 1000 Hz. This was due to the low-pass filtering effect of the annular slit. There was no significant change in the overall spray morphology for the gas inlet pulsation. By applying the same amplitude and frequency of pulsation to the gas and liquid inlets of the injector, the pulsation of the liquid inlet had a stronger effect on the injector exit spray than that of the gas inlet.

Investigation of the Behaviors of Methanol Spray Impingement and Wall Wetting

Port fuel injection is an important technical route in methanol engines. To obtain a theoretical basis for injector arrangement and injection strategy development in methanol engines, an optimal experimental platform based on diffuse back-illumination and the refractive index matching method (RIM) was designed and built in this study. The experiments on the behavior of low-pressure methanol spray-wall impingement and wall film were carried out and the influence of the three boundary conditions of spray distance (Dimp), wall temperature (Twall), and injection pressure (Pinj) were analyzed comprehensively. Results showed that with the increase of Dimp, the overall shape of spray before impinging the wall changed from conical to cylindrical. The impinging spray height Hi and impinging spray width Wi increased with the decrease of Dimp and the increase of Pinj. Adhesive fuel film mass Mf increased with the increase of Dimp due to the decrease of kinetic energy during wall impact. In addition, the increase of the wall temperature Twall reduced Mf due to evaporation, but when Twall reached 423 K, Mf rebounded due to the Leidenfrost effect. The results of this study are helpful to improve the accuracy of the numerical methanol engine model.

Effects of liquid properties on atomization and spray characteristics studied by planar two-photon fluorescence

In this work, planar two-photon laser-induced fluorescence (2p-LIF) is applied for the first time to analyze the fluid dependent spray structure and atomization behavior of water and ethanol in a quantitative way. A commercial six-hole DISI (Direct-Injection Spark-Ignition) injector was studied at different injection pressures, operated with liquids containing the LIF dye fluorescein. Specifically for DISI-injectors, the fluid-dependent atomization is very complex and not fully understood due to the cavitating, turbulent nozzle flow that dominates the spray formation. Optical access and analysis of the near-nozzle spray are often challenging due to multiple light scattering in dense regions which is reduced by 2p-LIF measurements using a femtosecond laser. This allows high-contrast spray imaging close to the nozzle, resulting in an improved identification of single liquid structures of the spray. Thus, a higher accuracy of sizing is possible. Compared to water, the ethanol spray shape shows increased cone angles in the nozzle near-field of about 6%, which cannot be explained by classical atomization theory based on aerodynamic breakup. The larger cone angle of ethanol was attributed to its larger viscosity, which could decelerate the flow at the wall of the injection hole, affecting the velocity profile of the emerging jet. The atomization shows a main jet breakup distance of 7–10 mm in which the structure sizes decreased drastically, specifically for water. For the size of the liquid structures in the near-nozzle region, which show dimensions of about 80–130 μm, ethanol exhibited about 2% smaller Feret's diameters than water for the tested time steps at 20 MPa. This effect is even more distinct for other injection pressures and positions at a further distance to the injector. For all investigated conditions and measurement positions downstream of the nozzle, ethanol showed on average about 24% smaller structures compared to the water spray. Although this trend is in accordance with the classical atomization theory based on the aerodynamic breakup mechanism, other effects, such as cavitation and nozzle-flow induced breakup, contribute to this behavior.

A comprehensive investigation of RANS and LES turbulence models for diesel spray modeling via experimental diesel schlieren imaging

Spray simulation is the basis of many engine simulations and directly impacts the quality of other simulations. Various models have been proposed to simulate spraying and the breakup and evaporation of fuel particles. The Kelvin–Helmholtz/Rayleigh–Taylor (KH-RT) model is one of the most common of these models. In this study, while analyzing the sensitivity of the KH-RT model constants on spray simulation, the effect of the LES and RANS turbulence model on spray penetration length and shape of the diesel spray contour is investigated. This study shows that both LES and RANS turbulence models along with the KH-RT model predict the spray penetration length with appropriate accuracy. While the RANS model, due to its averaging nature, does not accurately simulate the shape of the spray contour, which has very soft edges. Finally, the best method for simulating diesel spray and the proposed constants of the KH-RT model is presented.

Experimental Investigation on the Effects of Injection Parameters on the Air-Assisted Diesel Spray Characteristics

The air-assisted fuel injection (AAFI) system may be installed in the spark ignition aviation piston engine for the atomization of heavy fuels. However, studies on the effects of injection parameters on the spray characteristics are insufficient, which affects the improvement of AAFI engine performance. In this study, air-assisted diesel spray characteristics are investigated experimentally using a high-speed backlit imaging technique. The effects of main air-assisted injection control parameters such as fuel injection pressure, fuel temperature, and fuel injection duration on the spray characteristics are examined. The results show that spray shape changes from “spindle” to “cone” with an increase in fuel injection pressure. As the fuel injection pressure increases to 1.0 MPa, both the spray penetration and spray width increase significantly. “Protrusions” appear on the spray edge at high fuel temperatures. When the fuel temperature drops to 268 K, the spray penetration and spray width increase slightly. The spray shrinks significantly in both the axial and radial directions with an increase in fuel injection duration. Key parameters that directly affect air-assisted spray characteristics include the difference between the fuel-air mixture injection pressure and the ambient pressure, the density of fuel-air mixture in the air-assisted injector premixed chamber, and the kinetic energy density of the fuel. The former two parameters affect the spray penetration while the latter affects the spray width. The study is beneficial for the design of AAFI engines.

Numerical analysis of a water mist spray: The importance of various numerical and physical parameters, including the drag force

This paper presents a comprehensive set of numerical simulations for the characterization of a water mist spray emerging from a nozzle positioned at 2.2 m from floor level and operating at a pressure of 1.0 MPa. The droplet volume-median diameter is about 90 μm and the spray half-angle is around 42°. The spray shape is visualized using a laser sheet and the water flux density distribution on the ground is measured with a ‘bucket’ test. An initial comprehensive numerical study using the Fire Dynamics Simulator (FDS) has been carried out by varying several numerical and physical models and parameters (e.g., cell size and turbulence modelling). The simulated sprays were very narrow (in comparison to the actual spray), yielding overestimations of the peak water flux density at floor level by about 430% (on average). Subsequently, it was found that there is a significant impact of the drag force modelling because the spray at hand is dense (near the nozzle). An ad-hoc reduction of the drag coefficient to a constant value leads to better results. The current study calls upon new developments for droplet aerodynamic modelling in dense sprays.

A new model of fuel spray shape at early stage of injection in a marine diesel engine

PurposeIn the cylinders of a marine diesel engine, self-ignition occurs in a very short time after the fuel injection into the combustion chamber. Therefore, this paper aims to develop a model of diesel fuel spray for the early stage of fuel spray in the marine diesel engine. The main technical aspects such as nozzle diameter of the marine engine injector and backpressure in the combustion chamber were taken into consideration.Design/methodology/approachIn this paper, laboratory experimental studies were carried out to determine parameters of fuel spray in an early stage of injection in the marine diesel engine. The optical measuring Mie scattering technique was used to record the fuel injection process. The working space was a constant volume chamber. The backpressure parameters in the constant volume chamber were the same as during the operation of the marine diesel engine. Based on the experimental studies and important Hiroyasu and Arai models of fuel spray presented in literature was proposed new model of fuel spray parameters for marine diesel injectors.FindingsIn this paper, the proposed new model of the two main parameters described fuel spray evolution”: new model of spray tip penetration (STP) and spray cone angle (SCA). New model propagation of fuel STP in time was included the influence of nozzle diameter and backpressure. The proposed model has a lower error, about 15%–34%, than the model of Hiroyasu and Arai. Moreover, a new model of the evolution over time of the SCA is developed.Research limitations/implicationsIn the future research of fuel spray process must be taken influence of the fuel temperature. Diesel fuel has a different density and viscosity in dependence of fuel temperature. Therefore are predicted of the expansion about influence of fuel temperature, new model of fuel spray for a marine diesel engine. The main limitations occurring in the research are not possible to carry out the research while real operation marine diesel engine.Originality/valueAn experimental test was carried out for a real fuel injector of a marine diesel engine. Design parameters and fuel injection parameters were selected on the basis of the actual one. In the literature, SCA is defined as a constant parameter for the specific preliminary data. A new model for the early stage of fuel spray of SCA propagation in time has been proposed. The early stage of fuel spray is especially important, because in this time comes in there to fuel self-ignition.

Effect of geometric parameters on spray characteristics of air assisted pressure swirl atomizer

In the present work, a modified Pressure Swirl Atomizer (PSA) was introduced to operate as an Assisted Pressure Swirl Atomizer (AAPSA). Different mass flow rates of assisted air were experimentally tested. The studied parameters are the orifice length to diameter ratio (L/Do), swirl chamber length/diameter ratio (Ls/Ds) and swirling passage size (width × depth). The spray characteristics were studied using water as the atomized liquid. The spray was photographed using a high-speed camera to determine the spray shape, the cone angle and the spray breakup length. Moreover, photos taken by the high-speed camera were processed using IMAGE J software to obtain the droplet size diameters. The spray concentrations were measured by the patternator tubes technique. The results indicated that the spray cone angle increased by increasing the value of the L/Do ratio or by decreasing the assisted air mass flow rate. The spray concentration maximum value is shifted inward with the assist air injection. The breakup length decreased by about 65% for the PSA and 77% for the AAPSA when the value of the Ls/Ds ratio is decreased from 1.163 to 0.664. With the injection of assist air at a rate of 2 g/s, the Sauter Mean Diameter (SMD) is reduced by about 64% compared to a PSA having the same geometry.

Evaporating characteristics of diesel sprays under split-injection condition with a negative dwell time

This paper investigates the effects of the split-injection strategy with a negative dwell time using a multi-hole diesel injector under evaporating conditions. To compare with negative dwell conditions, the single-injection and positive and zero dwell conditions were adopted. The Laser Absorption Scattering (LAS) technique was employed to measure the temporal and spatial evolution of fuel evaporation and mixture concentration in the experiments. The split injection of 7:3 was selected according to the results of the previous study that proposed a homogeneous mixture after the end of injection. The dwell times of −50 us, 0 us, and 120 us were selected based on the measurement of the injection rate. The blended fuel consisting of 97.5% of n-tridecane and 2.5% of 1-methylnaphthalene in volume was used. The results show that a shorter spray tip penetration was present in the split injection with a negative dwell time. This phenomenon is expected to reduce the possibility of wall impingement and result in fewer nitrogen oxides (NOx) and unburned hydrocarbons (UHCs) under the injection conditions with a negative dwell time, especially for the conditions of a large injection amount and small-bore engines. Moreover, different spray shapes and behavior occurred in the case of different injection strategies. The spray of split-injection strategy with a negative dwell time has large radial dispersion, and it can improve the air utilization inside a cylinder.

Tool wear, economic costs, and CO2 emissions analysis in cryogenic assisted hard-turning process of AISI 52100 steel

Toward green manufacturing, the use of eco-friendly fluids such as cryogenic coolants is necessary for machining processes, instead of the use of conventional cutting fluids. The cryogenic spray method is most popular and, it can have high efficient for cooling cutting temperature and improving tool-life during machining operations. However, few studies have reported the benefits in terms of environment, cost for the cryogenic assisted hard turning processes. This study examines the economic and environmental impact of cryogenic cooling conditions on hard-turning machining. Liquid nitrogen was used as the cryogenic coolant. We examined the spray efficiency via computational fluid dynamics and experimental validation. The optimal nozzle for cryogenic spraying was found to have an internal angle of 45°. The nozzle of internal angle 45o has the highest distance and narrow width of spray shape in the results of computational fluid dynamics analysis and the experimental observation. Flank wear lengths were monitored under dry, wet, and cryogenic cooling conditions during the machining of AISI 52100 steel (62 HRC). The cryogenic assisted process improved ceramic cutting tool-life by 3–6 times compared to dry and wet conditions. The economic effects were also evaluated based on the tool-life data obtained. The improved tool life of the ceramic cutting tool by the cryogenic process reduced the total machine operation time; it thus reduced the electricity, carbon dioxide emissions of machine operations. The implementation of cryogenic cooling can be suitable for the green manufacturing process with the improvement of the environmental impact.

Numerical prediction of the spray from an air-assisted fuel injection system via Eulerian–Lagrangian approach

Air-assisted fuel injection (AAFI) systems may be installed in aviation piston engines for atomization of heavy fuels. However, there are few studies on the in-cylinder air-assisted spray characteristics, which affects the improvement of AAFI engine performance. In this study, an improved air-assisted spray simulation method based on ANSYS FLUENT was proposed to predict the changes in air-assisted spray characteristics alongside spray development, compared with previous simulations, the simulation in this paper was extended in both temporal and spatial domains and more accurate boundary conditions were given. The Eulerian–Lagrangian approach was used to represent the two-phase spray flow and a dynamic mesh model was used to simulate the movement of injector needle valve. The improved method was validated by comparison against experimental results in terms of spray shape, spray volume, spray penetration, spray droplet size spatial distribution, and overall Sauter mean diameter (SMD). By using the improved method, the average relative errors of the simulation results in spray volume and spray penetration were reduced by 13.5% and 10.2%, respectively. Additionally, some typical spray field parameters (gas phase pressure, gasified fuel mass fraction, etc.) were analyzed. The improved method can be used to study the in-cylinder air-assisted spray characteristics, which is beneficial for the fuel injection parameter optimization and the combustion chamber design of the AAFI engine.

The influence of in-cylinder flows and bulk gas density on early Spray G injection in an optical research engine

A well-characterized multi-hole gasoline injector, the Engine Combustion Network’s (ECN) Spray G injector, was investigated in an optically accessible research engine under four motored operating conditions with early injection. The experiments were conducted at intake pressures of [Formula: see text] and [Formula: see text], nearly matching the ECN’s standard early injection operating conditions, Spray G2 (flash boiling) and Spray G3 (early injection), respectively. This was combined with two engine speeds at [Formula: see text] and [Formula: see text]. Using particle image velocimetry and volumetric Mie scatter imaging, the in-cylinder flows were evaluated and the effects on the spray morphology were characterized. The in-cylinder flow was evaluated to understand the spray-flow interaction, including the turbulent kinetic energy. Little effect on turbulent energy was observed in the region examined near the exit of the fuel injector nozzle shortly after injection. Mie scatter imaging was used to characterize the spray morphology and wall wetting was clearly visible on the spark plug. Cyclic variability of the sprays was found to be insignificant; and major differences in spray morphology are attributed to the in-cylinder velocity and intake pressure at the time of injection. Decreasing the bulk gas density by decreasing the intake pressure had a number of effects on the evolution of the spray including faster evaporation, increased axial liquid penetration, and decreased spray angle. Increasing the in-cylinder flow magnitudes by increasing the engine speed had a similar effect on spray morphology by also increasing the evaporation rate, increasing the axial penetration, and decreasing the spray opening angle. Comparison of the motored spray cases with a no-flow case (when the fuel is sprayed into the engine without the piston present) further illustrated the extent to which the intake flow influenced the spray shape.

Numerical Analysis of GDI Flash Boiling Sprays Using Different Fuels

Modeling the fuel injection process in modern gasoline direct injection engines plays a principal role in characterizing the in–cylinder mixture formation and subsequent combustion process. Flash boiling, which usually occurs when the fuel is injected into an ambient pressure below the saturation pressure of the liquid, is characterized by fast breakup and evaporation rates but could lead to undesired behaviors such as spray collapse, which significantly effects the mixture preparation. Four mono–component fuels have been used in this study with the aim of achieving various flashing behaviors utilizing the Spray G injector from the Engine Combustion Network (ECN). The numerical framework was based on a Lagrangian approach and was first validated for the baseline G1 condition. The model was compared with experimental vapor and liquid penetrations, axial gas velocity, droplet sizes and spray morphology and was then extended to the flash boiling condition for iso–octane, n–heptane, n–hexane, and n–pentane. A good agreement was achieved for most of the fuels in terms of spray development and shape, although the computed spray morphology of pentane was not able to capture the spray collapse. Overall, the adopted methodology is promising and can be used for engine combustion modeling with conventional and alternative fuels.

A novel approach to improve environmentally friendly machining processes using ultrasonic nozzle–minimum quantity lubrication system

In minimum quantity lubrication (MQL) machining, a small quantity of cutting fluid is air-atomized to generate fine liquid droplets, and they are injected into the machining zone. The effectiveness of the MQL system depends on the droplet size/distribution, spray shape, spray velocity, and area fraction covered by the droplets. In the present study, for the first time, a novel MQL nozzle has been designed and manufactured applying ultrasonic vibrations using piezoelectric discs tighten on the nozzle between the mechanical amplifying element and a support element. Ultrasonic vibrations can be used to effectively atomize the cutting fluid into fine and uniform-sized droplets and smaller spray angle with a larger spray deposition distance. Ultrasonic nozzle–minimum quantity lubrication (UN-MQL) system generates a mist-like uniform spray. The ultrasonic nozzle was designed and analyzed using the SolidWorks and Ansys Workbench software. Image processing techniques have been used to characterize the droplet sizes, and the droplet distribution after the oil has been sprayed onto a polished lead-coated plate by UN-MQL system as well as better understanding in the application of the ultrasonic nozzle for its effective use in practical industrial applications. A set of experiments have been conducted on AISI 304L stainless steel during turning with the developed setup, and the results have been compared with dry, wet, and conventional MQL turning processes. The fine droplets produced by the UN-MQL system penetrate effectively into the machining zone and consequently enhance the cooling-lubrication characteristic in the cutting zone. Spray angle of UN-MQL in comparison to conventional MQL systems decreased about 40% and 30% in air pressure of 6 and 3 bar, respectively. The rising inclination of the area fraction covered by droplets in variable air pressures has improved approximately 70% among the oil flow rates of 16 to 110 ml/h in the UN-MQL case as opposed to the conventional MQL system. The greatest quantity of decrement in mean droplet diameter which transpired in air pressure of 1 bar, reached nearly 63% for the oil flow rates of 16 ml/h, 30 ml/h, and 43 ml/h. Overall, the results obtained during UN-MQL turning experiments show that the surface roughness has been improved compared to dry, flood, and conventional MQL turning processes.

Experimental analysis of the injection pressure effect on the near-field structure of liquid fuel sprays

Primary atomization and initial spray development are critical in the operation of high-pressure liquid sprays such as the ones used in internal combustion engines. In the current paper, an analysis of the effect of the fuel injection pressure on the near-nozzle spray morphology is performed. For this purpose, a high-magnification diffused backlight imaging technique is set by means of a high-speed light-emitting diode and a long-distance microscope. The technique allows to visualize the first 2 mm of the spray development with a resolution of approximately 250 pixels per millimeter. The images obtained are processed with two different criteria to define the spray contour: one using an optical thickness threshold and a second one based on the intensity derivative on the radial direction. The analysis is focused on three aspects of the spray morphology: the spray angle, its standard deviation, and the standard deviation of the spray contour itself. The results show that the average spray angle is only slightly affected by the injection pressure, being the discharge density the main boundary condition affecting this parameter. Instead, the two standard deviation parameters show a clear increasing trend with the injection pressure, confirming that higher turbulence at the nozzle outlet induces higher variability in the spray shape. Regarding the two contour detection methodologies, similar values are reached in the average spray angle, while some more impact is seen in the spray dispersion, although the same trends are found.

Non-intrusive optical measurements of gas turbine engine inlet condensation using machine learning

We demonstrate a novel application of supervised machine learning (ML) models to quantify the size, shape, number density, and distribution parameters of a water spray introduced at a gas turbine inlet. Only a limited set of laser scattering and extinction observations, acquired by pairs of photodetectors and cameras, are required for an accurate output. A phase Doppler particle analyzer as well as a conventional extinction inversion method are used to validate the particle size estimation, with the ML method converging closely to both. By measuring a water spray, where a spherical particle shape can be assumed, these size estimate validations could be made, which would have been difficult for a nonspherical particle measurement. By combining all the estimated parameters, the liquid volume fraction as well as the liquid flow rate is estimated and compared to a traceable ultrasonic flowmeter. To our knowledge, this is the first in situ condensation load measurement made at a gas turbine inlet without prior calibration. The ML approach is able to accurately estimate the liquid flow rate, with the majority of the estimates lying within the uncertainty bounds of the flowmeter and a root-mean-square difference of 0.8 L h−1 or 7.4%. Estimating the liquid flow rate using all the particle parameters demonstrates the method’s robustness and readiness for accurately measuring even nonspherical particles. The low number of required optical observations also makes this technique attractive for more generalized inlet particle measurements including sand, dust, and volcanic ash, in addition to condensation.