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At least 235 records · Page 13

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NASA NTRS1991

Dynamic behavior of liquid sheets

An experiment was conducted to study the aerodynamic instability of liquid sheets issuing from a two-dimensional air-assisted nozzle. Detailed measurements of the frequency of oscillation of the liquid sheet have been made. The measured vibrational frequencies were then correlated with the resulting spray angle. It was shown that the liquid sheet oscillations are dynamically similar to that of hard spring systems. For each air pressure, three distinct modes of breakup are distinguished. At low liquid flow rates, both the sinusoidal and the dilational modes are superimposed on the liquid sheet. With a further increase in liquid flow rate, the liquid sheet oscillations mainly become of the dilational type. It was also shown that the effect of introducing air in the nozzle is similar to the effect of inducing forced vibrations on the nozzle jaws. Thus, for each air flow rate, there is a specific vibration frequency for the nozzle. The frequency of these vibrations is proportional to the air velocity. As the liquid sheet natural frequency approaches that of the nozzle, resonance is established. At resonance, the maximum spray angle is achieved.

Mansour, Adel↗

NASA NTRS1999

Formation of Sprays From Conical Liquid Sheets

Our objective is to predict droplet size distributions created by fuel injector nozzles in Jet turbines. These results will be used to determine the initial conditions for numerical simulations of the combustion process in gas turbine combustors. To predict the droplet size distribution, we are currently constructing a numerical model to understand the instability and breakup of thin conical liquid sheets. This geometry serves as a simplified model of the liquid jet emerging from a real nozzle. The physics of this process is difficult to study experimentally as the time and length scales are very short. From existing photographic data, it does seem clear that three-dimensional effects such as the formation of streamwise ligaments and the pulling back of the sheet at its edges under the action of surface tension are important.

Peck, Bill↗

NASA NTRS1976

Oil-air mist lubrication for helicopter gearing

The applicability of a once-through oil mist system to the lubrication of helicopter spur gears was investigated and compared to conventional jet spray lubrication. In the mist lubrication mode, cooling air was supplied at 366K (200 F) to the out of mesh location of the gear sets. The mist air was also supplied at 366K (200 F) to the radial position mist nozzle at a constant rate of 0.0632 mol/s (3 SCFM) per nozzle. The lubricant contained in the mist air varied between 32 - 44 cc/hour. In the recirculating jet spray mode, the flow rate was varied between 1893 - 2650 cc/hour. Visual inspection revealed the jet spray mode produced a superior surface finish on the gear teeth but a thermal energy survey showed a 15 - 20% increase in heat generated. The gear tooth condition in the mist lubrication mode system could be improved if the cooling air and lubricant/air flow ratio were increased. The test gearbox and the procedure used are described.

Mcgrogan, F.↗

NASA NTRS1992

Effect of gas mass flux on cryogenic liquid jet breakup

A scattered-light scanning instrument developed at NASA Lewis Research Center was used to measure the characteristic drop size of clouds of liquid nitrogen droplets. The instrument was calibrated with suspensions of monosized polystyrene spheres. In this investigation of the mechanism of liquid nitrogen jet disintegration in a high-velocity gas flow, the Sauter mean diameter, D32, was found to vary inversely with the nitrogen gas mass flux raised to the power 1.33. Values of D32 varied from 5 to 25 microns and the mass flux exponent of 1.33 agrees well with theory for liquid jet breakup in high-velocity gas flows. The loss of very small droplets due to the high vaporization rate of liquid nitrogen was avoided by sampling the spray very close to the atomizer, i.e., 1.3 cm downstream of the nozzle orifice. The presence of high velocity and thermal gradients in the gas phase also made sampling of the particles difficult. As a result, it was necessary to correct the measurements for background noise produced by both highly turbulent gas flows and thermally induced density gradients in the gas phase.

Ingebo, R. D.↗

NASA NTRS1986

Water jet/spray measurement analysis

The objective of this study was to provide analysis of data obtained under a previous contract entitled Characterization of Drop Spectra from High Volume Flow Water Jets. Measurements of drop spectra were obtained in the spray resulting from the breakup of high volume flow water jets from a variety of nozzle types. The drop spectra measurements were obtained from two drop spectrometers covering a range from 10 microns to 12 millimeters diameter. The task addressed was to select representative spectra from the individual tests and provide analyses in both numerical and graphical formats as outlined in the proposal. The intended application of these results is an evaluation of the feasibility of fog clearing by high volume water sprays. During the tests, a fog event occurred making it possible to test the concept of fog clearing. Visual range data and fog drop spectra were analyzed, with particular emphasis placed on the modification of these parameters due to the water spray.

Lala, G. G.↗

DOE OSTI2022

Experimental Investigation of the Effect of Atomizing Electrospray Nozzles on the Cooling and Reduced Humidification of Air

Separating sensible and latent cooling have shown the potential to reduce energy consumption in A/C systems for building HVAC applications. Several technologies exist based on vapor-compression refrigeration, enthalpy wheels, chemical adsorption and absorption materials, and mechanical cooling. However, their thermodynamics limits and high energy consumption hinder their deployment in hot and humid climatic regions. This paper focuses on separating sensible and latent cooling by using a new thermodynamics process and in-kind (i.e., non-vapor compression-based) technology. Highly electrically charged water droplets were sprayed in the airflow. These droplets attracted water vapor molecules to their surfaces and promoted condensation. The phenomenon was the result of simultaneous dielectrophoresis and electro-diffusion interactions. Studies in the literature have shown that using multiple capillary electrodes reduced air moisture by up to 5% when using nanometer-size droplets in the spray. Unfortunately, these studies were limited to low airflow rates, and the objective of this paper was to investigate how to scale up this in-kind approach to airflows typical of buildings. In the present paper, droplets of micrometer size were utilized to control the humidity for a 5-cfm flow rate. While this airflow was still low for building applications, it was 100 times fold the airflows in the literature studies. The air was tested at 20°C and at 50 and 80% relative humidity. A two-fluid atomizing nozzle produced the droplets in the spray, and high DC electric potential, up to 25 kV, was used to charge the fine droplets electrically. The air atomizing nozzle with high voltage potential resembled an evaporative cooler process. However, a measurable reduction of the absolute humidity of up to 2% was observed compared to the case of the nozzle with no high voltage potential. The entire device had one small nozzle selected from off-the-shelf components and had less than a 9 cm2 footprint area.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2023

Detailed mixing measurements from single-hole converging ECN injectors using Rayleigh scattering

Time resolved liquid and vapor fields of dodecane and oxymethylene ethers are measured from Spray A-3 and Spray D using high speed Rayleigh scattering and diffuse back illumination at the Engine Combustion Network (ECN) Spray A condition of 900 K and 22.8 kg/m 3 . Global quantities including mixture fraction, vapor and liquid penetration, as well as spreading angle are measured. The mixture fraction fields and vapor penetration profiles are well predicted by the 1-D Musculus-Kattke model. The mixture fraction field and vapor penetration from Spray A-3 are similar to those measured from Spray A in previous works. Spray D exhibits higher mixture fraction fields and vapor penetration due to its larger nozzle diameter. The quasi-steady mixture fraction fields from these injectors scale well when distance from the injector is normalized by the nozzle diameter. The turbulent dissipation structures were also analyzed based on the orientation, thickness, and magnitude of the mixing layers. Furthermore, the orientation and thickness are similar to other measurements in atmospheric gas jets, while the magnitude is lower. The thickness and magnitude are subject to uncertainties due to limitations in the imaging resolution of the system but still provide an order of magnitude as a useful reference for comparison against computational fluid dynamic simulations.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2026

Time-resolved spray characterization via unified optical flow and binarization technique

This work leverages an unsupervised machine learning and advanced image processing techniques to characterize the breakup of fuel sprays in a small-scale combustor under reacting conditions, providing valuable insights into near-nozzle flow phenomenology. The proposed methodology integrates an improved optical flow model on a convolutional neural network to extract flow vectors with a binarization technique to assess droplets’ size and shape across the region of interest. The velocimetry approach demonstrates superior performance compared to a state-of-the-art optical flow model when applied to high-speed X-ray phase contrast spray images, achieving more accurate and reliable flow predictions. Moreover, breakup processes are quantified by breakup length and sphericity in accordance with velocity estimations, allowing a more complete characterization of the flow. This study establishes a robust methodology for analyzing spray morphology and primary breakup in compact combustors, contributing valuable means of understanding and optimizing fuel spray behavior in advanced combustion systems.

42 ENGINEERING↗

NASA NTRS1994

Structure of a Swirl-stabilized, Combusting Spray

Measurements of the structure of a swirl-stabilized, reacting spray are presented. The configuration consisted of a research air-assist atomizer located in the center surrounded by a coflowing air stream. Both the air assist and coflow streams had swirl imparted to them in the same direction with 45 degree angle swirlers. The fuel and air entered the combustor at ambient temperature and the combustor was operated in an unconfined environment. The gas phase was seeded with aluminum oxide particles in order to obtain velocity measurements. Velocity measurements for the gas phase are reported for both an isothermal, single-phase case without drops and a reacting spray case at axial distances from 2.5 to 350 mm downstream of the nozzle. Both mean and fluctuating values are reported. Heptane fuel was used for all the experiments. Drop size and velocity, and drop number flux are also reported for five axial distances downstream. Both mean and fluctuating values are reported for the drops. The measurements were performed using a two-component phase/Doppler particle analyzer. Profiles across the entire flowfield where velocities were significant are presented. Mean gas phase temperatures were also measured intrusively using a single pt/pt-13 percent rh thermocouple and are reported at axial distances from 2.5 to 200 mm downstream of the nozzle.

Bulzan, Daniel L.↗

NASA NTRS1995

Structure of a swirl-stabilized combusting spray

Measurements of the structure of a swirl-stabilized, reacting spray are presented. The configuration consisted of a research air-assist atomizer located in the center surrounded by a co-flowing airstream. Both the air-assist and co-flowing streams had swirl imparted to them in the same direction with 45-deg angle swirlers. The fuel and air entered the combustor at ambient temperature and the combustor was operated in an unconfined environment. The gas phase was seeded with aluminum-oxide particles in order to obtain velocity measurements. Mean velocity measurements for the gas phase are reported for both an isothermal, single-phase case without drops and a reacting spray case at axial distances from 2.5 to 50 mm downstream of the nozzle. Heptane fuel was used for all the experiments. Drop size and mean velocity and drop number flux are also reported for five axial distances downstream. The measurements were performed using a two-component phase/Doppler particle analyzer. Profiles across the entire flowfield where velocities were significant are presented. Mean gas-phase temperatures were also measured intrusively using a single pt/pt-13%rh thermocouple and are also reported at axial distances from 2.5 to 50 "im downstream of the nozzle.

Bulzan, Daniel L.↗

DOE OSTI2024

Breakup dynamics in a pressure-swirl injector for urea-water solution applications: A computational study

The co-optimization of in-cylinder combustion and after-treatment technology has become a major aspect in engine design and development, with the goal of meeting the increasingly restrictive emission regulations in the transportation industry. Selective Catalytic Reduction is a robust technology to control the emission of NO x , and the injection of urea in water solution is the exhaust tailpipe is a key aspect of its operation. The proposed work uses high-fidelity Computational Fluid Dynamics to characterize the atomization dynamics of the liquid jet in relevant cross-flow conditions. The study focuses on a commercial low-pressure (9 bar) pressure-swirl injector which is characterized in its internal geometry through high-resolution X-ray micro-computational tomography. The internal two-phase flow has been modeled according to the volume-of-fluid approach in a large eddy simulation framework and validated against near-nozzle X-ray radiography measurement. Moreover, characterizing the breakup dynamics for the swirling hollow cone formation, and assessing the influence of the cross-flow in the breakup dynamics was completed. The results have been reported proposing Re-Oh maps and probability density functions of the spray kinematics. Higher cross-flow momentum generates an increase in the jet intact length and a reduction of the liquid droplet diameters. The axial momentum of the jet is affected by the cross-flow already in the near-nozzle region, determining a relevant deviation of the spray velocities. In conclusion, this work aims to inform the initialization of Eulerian-Lagrangian spray models through the assignment of droplet kinematics and static one-way coupling between volume-of-fluid results and Lagrangian spray parcels, to be used for system-size domain simulations.

33 ADVANCED PROPULSION SYSTEMS↗

NASA NTRS2011

Assessment of Some Atomization Models Used in Spray Calculations

The paper presents the results from a validation study undertaken as a part of the NASA s fundamental aeronautics initiative on high altitude emissions in order to assess the accuracy of several atomization models used in both non-superheat and superheat spray calculations. As a part of this investigation we have undertaken the validation based on four different cases to investigate the spray characteristics of (1) a flashing jet generated by the sudden release of pressurized R134A from cylindrical nozzle, (2) a liquid jet atomizing in a subsonic cross flow, (3) a Parker-Hannifin pressure swirl atomizer, and (4) a single-element Lean Direct Injector (LDI) combustor experiment. These cases were chosen because of their importance in some aerospace applications. The validation is based on some 3D and axisymmetric calculations involving both reacting and non-reacting sprays. In general, the predicted results provide reasonable agreement for both mean droplet sizes (D32) and average droplet velocities but mostly underestimate the droplets sizes in the inner radial region of a cylindrical jet.

Raju, M. S.↗

NASA NTRS1988

Warm fog dissipation using large volume water sprays

To accomplish the removal of warm fog about an area such as an airport runway, a plurality of nozzles along a line adjacent the area propelled water jets through the fog to heights of approximately twenty-five meters. Each water jet breaks up forming a water drop size distribution that falls through the fog overtaking, colliding, and coalescing with individual fog droplets and thereby removes the fog. A water retrieval system is used to collect the water and return it to reservoirs for pumping it to the nozzles once again.

Vernon W Keller↗

NASA NTRS1930

Effect of Orifice Length-Diameter Ratio on Spray Characteristics

The effect of variations of orifice length to diameter ratio on spray characteristics was determined for a 0.014-inch and a 0.040-inch orifice for ratio of 0.5 to 4.0. The nozzles containing the orifices were mounted in an injection valve and tested with a plan stem and with a helically grooved stem. The injection pressure was varied from 4000 to 8000 pounds per square inch. The air density into which the fuel was sprayed was varied from the density obtained with a pressure of 60 pounds per square inch to the density obtained with a pressure of 250 pounds per square inch at room temperature. The tests showed that increasing the orifice length to diameter ratio with a plain stem in the injection valve causes the spray tip penetration first to decrease, reaching a minimum between a ratio of 1.5 and 2.5, and then to increase, reaching a maximum at a ratio greater than 3.5. The spray cone angle showed little change with variation of the ratio. With a helically grooved stem and small ratio of orifice area to groove area, the penetration at first shows little tendency towards a minimum; but as the time of injection is increased to 0.004 second, the penetration becomes a minimum at a ratio between 0.5 and 2.0.

Gellales, A G↗

NASA NTRS1994

Design of high pressure waterjet nozzles

The Hydroblast Research Cell at Marshall Space Flight Center is used to investigate the use of high pressure waterjets to strip paint, grease, adhesive and thermal spray coatings from various substrates. Current methods of cleaning often use ozone depleting chemicals (ODC) such as chlorinated solvents. High pressure waterjet cleaning has proven to be a viable alternative to the use of solvents. A popular method of waterjet cleaning involves the use of a rotating, multijet, high pressure water nozzle which is robotically controlled. This method enables rapid cleaning of a large area, but problems such as incomplete coverage and damage to the substrate from the waterjet have been observed. This report summarizes research consisting of identifying and investigating the basic properties of rotating, multijet, high pressure water nozzles, and how particular designs and modes of operation affect such things as stripping rate, standoff distance and completeness of coverage. The study involved computer simulations, an extensive literature review, and experimental studies of different nozzle designs.

Mazzoleni, Andre P.↗

DOE OSTI2024

Spray process of multi-component gasoline surrogate fuel under ECN Spray G conditions

As modern gasoline direct injection (GDI) engines utilize sophisticated injection strategies, a detailed understanding of the air-fuel mixing process is crucial to further improvements in engine emission and fuel economy. In this study, a comprehensive evaluation of the spray process of single-component iso-octane (IC8) and multi-component gasoline surrogate E00 (36 % n-pentane, 46 % iso-octane, and 18 % n-undecane, by volume) fuels was conducted using an Engine Combustion Network (ECN) Spray G injector. High-speed extinction, schlieren, and microscopy imaging campaigns were carried out under engine-like ambient conditions in a spray vessel. Experimental results including liquid/vapor penetration, local liquid volume fraction, droplet size, and projected liquid film on the nozzle tip were compared under ECN G1 (573 K, 3.5 kg/m 3 ), G2 (333 K, 0.5 kg/m 3 ), and G3 (333 K, 1.01 kg/m 3 ) conditions. In addition to the experiments, preferential evaporation process of the E00 fuel was elucidated by Large–Eddy Simulations (LES). The three-dimensional liquid volume fraction measurement enabled by the computed tomographic reconstruction showed substantial plume collapse for E00 under the G2 and G3 conditions having wider plume growth and plume-to-plume interaction due to the fuel high vapor pressure. Here, the CFD simulation of E00 showed an inhomogeneity in the way fuel components vaporized, with more volatile components carried downstream in the spray after the end of injection. The high vapor pressure of E00 also results in ~4 μm smaller average droplet diameter than IC8, reflecting a higher rate of initial vaporization even though the final boiling point temperature is higher. Consistent with high vapor pressure, E00 had a wider plume cone angle and enhanced interaction with the wall to cover the entire surface of the nozzle tip in a film. However, the liquid fuel underwent faster evaporation, so the final projected tip wetting area was smaller than the IC8 under the flash-boiling condition.

33 ADVANCED PROPULSION SYSTEMS↗

NASA NTRS1977

Atomization of water jets and sheets in axial and swirling airflows

Axial and swirling airflows were used to break up water jets and sheets into sprays of droplets to determine the overall effects of orifice diameter, weight flow of air, and the use of an air swirler on fineness of atomization as characterized by mean drop size. A scanning radiometer was used to determine the mean drop diameter of each spray. Swirling airflows were produced with an axial combustor, 70 deg blake angle, air swirling. Water jets were injected axially upstream, axially downstream and cross stream into the airflow. In addition, pressure atomizing fuel nozzles which produced a sheet and ligament type of breakup were investigated. Increasing the weight flow rate of air or the use of an air swirling markedly reduced the spray mean drop size.

Ingebo, R. D.↗

NASA NTRS1979

Atomization of water jets and sheets in axial and swirling airflows

Ingebo, R. D.↗