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NASA NTRS2025

Radiation-Resistant Ti/BN Coatings: Insights From 171 Days Exposure to Space Radiation and Atomic Oxygen in Low Orbit

Atmospheric Plasma Spray (APS) and Vacuum Plasma Spray (VPS) techniques were used to develop Ti/2 vol.% hBN coatings, for extreme space environments and tested aboard the International Space Station as part of the MISSE-17 (Materials International Space Station Experiments) program. The coatings were exposed to atomic oxygen, space radiation, and low-orbit thermal cycling. VPS coatings showed a 56% increase in microhardness, a 26% rise in elastic modulus, minimal porosity and crack density changes compared to APS coatings. The change in mechanical properties is attributed to the formation of TiO, TiO₂ and TiN from nitrogen retention, alongside radiation-induced dislocations, which enhanced surface hardening. The oxidation of titanium led to the formation of TiO and TiO₂, while boron nitride was retained and underwent transmutation in VPS coatings. XPS and EDS analyses confirmed the enhanced space-environment resistance of VPS coatings, making them ideal for long-term spacecraft protection in lunar and Martian conditions.

Abhijith Kunneparambil Sukumaran↗
NASA NTRS2006

Cold Flow Testing for Liquid Propellant Rocket Injector Scaling and Throttling

Scaling and throttling of combustion devices are important capabilities to demonstrate in development of liquid rocket engines for NASA's Space Exploration Mission. Scaling provides the ability to design new injectors and injection elements with predictable performance on the basis of test experience with existing injectors and elements, and could be a key aspect of future development programs. Throttling is the reduction of thrust with fixed designs and is a critical requirement in lunar and other planetary landing missions. A task in the Constellation University Institutes Program (CUIP) has been designed to evaluate spray characteristics when liquid propellant rocket engine injectors are scaled and throttled. The specific objectives of the present study are to characterize injection and primary atomization using cold flow simulations of the reacting sprays. These simulations can provide relevant information because the injection and primary atomization are believed to be the spray processes least affected by the propellant reaction. Cold flow studies also provide acceptable test conditions for a university environment. Three geometric scales - 1/4- scale, 1/2-scale, and full-scale - of two different injector element types - swirl coaxial and shear coaxial - will be designed, fabricated, and tested. A literature review is currently being conducted to revisit and compile the previous scaling documentation. Because it is simple to perform, throttling will also be examined in the present work by measuring primary atomization characteristics as the mass flow rate and pressure drop of the six injector element concepts are reduced, with corresponding changes in chamber backpressure. Simulants will include water and gaseous nitrogen, and an optically accessible chamber will be used for visual and laser-based diagnostics. The chamber will include curtain flow capability to repress recirculation, and additional gas injection to provide independent control of the backpressure. This paper provides a short review of the appropriate literature, as well as descriptions of plans for experimental hardware, test chamber instrumentation, diagnostics, and testing.

Kenny, Jeremy R.↗
NASA NTRS2019

Design of Experiment for the Measurement of Aerosol Droplet Size Distribution of Temperature-Controlled Thermally Atomized Printed Electronic Inks

In-Space Manufacturing (ISM) centers around NASA’s growing need and ability to produce space technologies on demand in space. As the future of long term presence in space and deep space exploration approach, fundamental questions of our dependence on earth resupply to Low Earth Orbit (LEO) remain unanswered. ISM is leading various effort to evaluate the feasibility of producing essential spares and redundant parts on demand to enable a sustainable space-based supply chain model for part resupply. Among the parts and systems being considered, Avionics form the neural network of modern day aircraft and space vehicles providing a wealth of information ranging from Guidance, Navigation, and Control (GN&C) systems to on board Environmental Control and Life Support (ECLS) systems. Recent advances in the use of Aerosol Jet Technology to print Avionics components ranging from electrical traces on a circuit board to complex transistors and sensors raise the possibility of using such technology to reproduce or recreate electronic parts on demand with the help of custom electronics 3D printers. The challenge herein lies within the ability of such printers to generate and deposit an aerosol of electronic material utilizing processes independent of or enhanced by gravity to ensure controllably identical or improved behavior of the aerosol in an International Space Station (ISS) laboratory and on the ground. The behavior as well as the hazards and properties associated with such aerosols in a microgravity environment must be understood well in order to merit a feasible approach to utilizing them for manufacturing in space. In this report, we outline the experimental setup of a modified conventional vaping device to be used as the ideal gravity independent thermal atomization mechanism to generate aerosol. Our objective is to identify the ideal mass, density, and volume of our aerosolized droplets of ink to conclude that there exist a threshold of aerosolized ink droplet sizes that are indeed independent of the effects of gravity and remain stable after atomization. We use a Malvern Spraytec® Spray Particle Size Analyzer to perform real-time laser diffraction measurement of our ink droplets during atomization. The droplet size between conductive ink, dielectric ink and vegetable glycerin have been measured and contrasted. Furthermore, the mechanism of thermal atomization versus traditional pneumatic and ultrasonic atomization for operation in microgravity have been explored.

Wu, Chih-Hao↗
NASA NTRS1989

Gas-phase flowrate effect on disintegrating cryogenic liquid-jets

Two phase liquid and gaseous nitrogen flow in a pneumatic two fluid atomizer was investigated. Characteristic dropsize for cryogenic sprays were measured with a scattered light scanning instrument developed at NASA-Lewis. Tests were conducted primarily in the aerodynamic stripping regime of liquid jet atomization. At a sampling distance of bar-x=1.3 cm, the Sauter mean, D(sub 32), and volume median, D(sub v.5), drop diameters were measured and correlated with nitrogen gas flowrate, W(sub n), to give the following expressions: D sub 32 to the -1=210W(sub n) to the -1.33 and D(sub v.5) to the -1=150 W(sub n to the -1.33, where reciprocal diameters and gas flowrate are in cm (-1) and g/sec, respectively. The exponent 1.33 for nitrogrn gas flowrate, W(sub n), is the same as that predicted by atomization theory for liquid-jet breakup in high velocity gasflow. When the spray was sampled at axial distances of bar-x=2.5 and 4.5 cm downstream of the atomizer, the exponent decreased to 1.2 and 0.9, respectively. This was attributed to the loss of small droplets due to their rapid vaporization.

Ingebo, Robert D.↗
NASA NTRS1990

Gas-phase flowrate effect on disintegrating cryogenic liquid-jets

Two phase liquid and gaseous nitrogen flow in a pneumatic two fluid atomizer was investigated. Characteristic dropsize for cryogenic sprays were measured with a scattered light scanning instrument developed at NASA-Lewis. Tests were conducted primarily in the aerodynamic stripping regime of liquid jet atomization. At a sampling distance of bar-x =1.3 cm, the Sauter mean, D(sub 32), and volume median, D(sub v.5), drop diameters were measured and correlated with nitrogen gas flowrate, W(sub n), to give the following expressions: D sub 32 to the -1=210W(sub n) to the -1.33 and D(sub v.5) to the -1=150 W(sub n to the -1.33, where reciprocal diameters and gas flowrate are in cm (-1) and g/sec, respectively. The exponent 1.33 for nitrogen gas flowrate, W(sub n), is the same as that predicted by atomization theory for liquid-jet breakup in high velocity gasflow. When the spray was sampled at axial distances of bar-x=2.5 and 4.5 cm downstream of the atomizer, the exponent decreased to 1.2 and 0.9, respectively. This was attributed to the loss of small droplets due to their rapid vaporization.

Ingebo, Robert D.↗
NASA NTRS1993

The electrospray: Fundamentals and combustion applications

Liquid fuel dispersion in practical systems is typically achieved by spraying the fuel into a polydisperse distribution of droplets evaporating and burning in a turbulent gaseous environment. In view of the nearly unsurmountable difficulties of this two-phase flow, it would be useful to use an experimental arrangement that allow a systematic study of spray evolution and burning in configurations of gradually increasing levels of complexity, starting from laminar sprays to fully turbulent ones. An Electrostatic Spray (ES) of charged droplets lends itself to this type of combustion experiments under well-defined conditions and can be used to synthesize gradually more complex spray environments. In its simplest configuration, a liquid is fed into a small metal tube maintained at several kilovolts relative to a ground electrode few centimeters away. Under the action of the electric field, the liquid meniscus at the outlet of the capillary takes a conical shape, with a thin jet emerging from the cone tip. This jet breaks up farther downstream into a fine spray of charged droplets. Several advantages distinguish the electrospray from alternative atomization techniques: the self-dispersion property of the spray due to coulombic repulsion; the absence of droplet coalescence; the potential control of the trajectories of charged droplets by suitable disposition of electrostatic fields; and the decoupling of atomization, which is strictly electrostatic, from gas flow processes. Furthermore, as recently shown in our laboratory, the electrospray can produce quasi-monodisperse droplets over a very broad size range (1-100 microns). The ultimate objective of this research project is to study the formation and burning of electrosprays of liquid fuels first in laminar regimes and then in turbulent ones. Combustion will eventually be investigated in conditions of three-dimensional droplet-droplet interaction, for which experimental studies have been limited to either qualitative observations in sprays or more quantitative observations on simplified systems consisting of a small number of droplets or droplet arrays. The compactness and potential controllability of this spray generaiton system makes it appealing for studies to be undertaken in the next two years on electrospray combustion in reduced-gravity environments such as those achievable at NASA microgravity test facilities.

Gomez, Alessandro↗
NASA NTRSDate not supplied

Comparison of Non-Combusting Spray Fields in a Model Combustor using Shadowgraphy

Droplet sizes were measured using shadowgraphy in the spray issuing from the center element of the baseline configuration of the NASA 7-element lean direct injector (LDI) array. Each LDI element consisted of a 60 degree clockwise axial air swirler, converging-diverging venturi, and a pressure-swirl atomizer positioned with its tip at the venturi throat. The non-combusting measurements were conducted using water spray in a 3-inch diameter research combustor operating at pressure of 5 bar and air inlet temperature of 700 K. At these inlet conditions, three air flow rates were used, producing reference velocities of 7.6, 15.2, and 22.9 m/s. Only the center nozzle was used. At each reference velocity, water flow rates were adjusted to simulate a common equivalence. Data were collected at a frame rate of 15 Hz over a range of positions near the LDI dump plane, and downstream, along the combustor centerline. Velocity measurements were achieved by use of a dual head Nd:YAG laser and frame transfer PIV camera. Droplet size and velocity, mass and number density, and volume fraction are compared at these inlet conditions to determine the effect of nozzle pressure drop on the measured properties.

lean direct injection↗
NASA NTRSDate not supplied

Comparison of Non-Combusting Spray Fields in a Model Combustor using Shadowgraphy

Droplet sizes were measured using shadowgraphy in the spray issuing from the center element of the baseline configuration of the NASA 7-element lean direct injector (LDI) array. Each LDI element consisted of a 60 degree clockwise axial air swirler, converging-diverging venturi, and a pressure-swirl atomizer positioned with its tip at the venturi throat. The non-combusting measurements were conducted using water spray in a 3-inch diameter research combustor operating at pressure of 5 bar and air inlet temperature of 700 K. At these inlet conditions, three air flow rates were used, producing reference velocities of 7.6, 15.2, and 22.9 m/s. Only the center nozzle was used. At each reference velocity, water flow rates were adjusted to simulate a common equivalence. Data were collected at a frame rate of 15 Hz over a range of positions near the LDI dump plane, and downstream, along the combustor centerline. Velocity measurements were achieved by use of a dual head Nd:YAG laser and frame transfer PIV camera. Droplet size and velocity, mass and number density, and volume fraction are compared at these inlet conditions to determine the effect of nozzle pressure drop on the measured properties.

lean direct injection↗
NASA NTRS1971

Correlation of spray dropsize distribution and injector variables

The atomization characteristics of impinging stream rocket engine injection elements are studied to determine the effects of hydraulic and geometric parameters on the mass median drop size. The major conclusions are: (1) the velocity profile of impinging jets affects mean drop size, this effect is greater when the jets are laminar than when they are turbulent; (2) the drop size/injection velocity dependence for turbulent jet impingement differs from that obtained with non-turbulent jets; (3) the level of turbulence intensity does not affect mean drop size; (4) the impingement of disintegrated or nearly disintegrated jets substantially decreases atomization; and (5) even though an emulsion is formed when immiscible jets impinge, the level of emulsification is small.

Zajac, L. J.↗
NASA NTRS1988

Chlorine-hydrocarbon photochemistry in the marine troposphere and lower stratosphere

The role of chlorine atoms in the oxidation of methane and nonmethane hydrocarbons (NMHCs) in the marine troposphere and lower stratosphere was investigated using a one-dimensional photochemical model that incorporated the chemistry of CH4, NMHCs, NO(x), O(x), and HO(x), as well as organic and inorganic halogens in the troposphere and lower stratosphere. The model predicted that chlorine atoms are present in the marine troposphere at the concentrations of about 1000/cu cm, mostly as a product of the reaction between OH and HCl released from sea spray. The results indicate that Cl atoms cause 20 to 40 percent of NMHC oxidation in the troposphere and 40 to 90 percent in the lower stratosphere. At 15 km, the NMHC-Cl reactions account for nearly 80 percent of the PAN produced. Where available, experimental data confirmed the model predictions.

Singh, H. B.↗
NASA NTRS1984

Aviation-fuel property effects on combustion

The fuel chemical property influence on a gas turbine combustor was studied using 25 test fuels. Fuel physical properties were de-emphasized by using fuel injectors which produce highly-atomized, and hence rapidly vaporizing sprays. A substantial fuel spray characterization effort was conducted to allow selection of nozzles which assured that such sprays were achieved for all fuels. The fuels were specified to cover the following wide ranges of chemical properties: hydrogen, 9.1 to 15 (wt) pct; total aromatics, 0 to 100 (vol) pct; and naphthalene, 0 to 30 (vol) pct. standard fuels (e.g., Jet A, JP4), speciality products (e.g., decalin, xylene tower bottoms) and special fuel blends were included. The latter group included six, 4-component blends prepared to achieve parametric variations in fuel hydrogen, total aromatics and naphthalene contents. The principle influences of fuel chemical properties on the combustor behavior were reflected by the radiation, liner temperature, and exhaust smoke number (or equivalently, soot number density) data. Test results indicated that naphthalene content strongly influenced the radiative heat load while parametric variations in total aromatics did not.

Rosfjord, T. J.↗
NASA NTRS1984

Influence of fuel chemical properties on gas turbine combustors

In an attempt to rigorously study the fuel chemical property influence, UTRC (United Technologies Research Center) (under contract to NASA Lewis Research Center) has conducted an experimental program using 25 test fuels. The burner was a 12.7 cm dia cylindrical device consisting of six sheet metal louvers. A single pressure atomizing injector and air swirler were centrally mounted with the conical dome. Fuel physical properties were de-emphasized by using fuel injectors which produced highly atomized, and hence rapidly vaporizing sprays. A substantial fuel spray characterization effort was conducted to allow selection of nozzles which assured that such sprays were achieved for all fuels. The fuels were specified to cover the following wide ranges of chemical properties: hydrogen, 9.1 to 15 (wt) pct; total aromatics, 0 to 100 (vol) pct; and naphthalene, 0 to 30 (vol) pct. They included standard fuel (e.g., Jet A, JP4), specialty products (e.g., decalin, xylene tower bottoms) and special fuel blends. Included in this latter group were six, 4-component blends prepared to achieve parametric variations in fuel hydrogen, total aromatics and naphthalene contents.

Rosfjord, T. J.↗
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 NTRS2006

A New Finite-Conductivity Droplet Evaporation Model Including Liquid Turbulence Effect

A new approach to account for finite thermal conductivity and turbulence effects within atomizing droplets of an evaporating spray is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen [9]. This finite conductivity model is based on the two-temperature film theory in which the turbulence characteristics of the droplet are used to estimate the effective thermal diffusivity for the liquid-side film thickness. Both one-way and two-way coupled calculations were performed to investigate the performance cf this model against the published experimental data.

Balasubramanyam, M. S.↗
NASA NTRS1985

Measurements and predictions of the structure of evaporating sprays

In the present experimental and theoretical study of turbulent, evaporating sprays, round, Freon-11 sprays produced by an air-atomizing injector that is directed vertically downward in still air were subjected to structure measurements for mean and fluctuating gas velocities, total Freon-11 concentration, drop size and velocity contributions, mean gas temperature, and liquid flux distributions. An evaluation was then conducted of three spray models: (1) locally homogeneous flow, (2) deterministic separated flow, and (3) stochastic separated flow. The first two of these were found to perform poorly; the stochastic model yielded the best agreement between predictions and measurements.

Solomon, A. S. P.↗
NASA NTRS1979

Spray nozzle designs for agricultural aviation applications

Techniques of generating monodisperse sprays and information concerning chemical liquids used in agricultural aviation are surveyed. The periodic dispersion of liquid jet, the spinning disk method, and ultrasonic atomization are the techniques discussed. Conceptually designed spray nozzles for generating monodisperse sprays are assessed. These are based on the classification of the drops using centrifugal force, on using two opposing liquid laden air jets, and on operating a spinning disk at an overloaded flow. Performance requirements for the designs are described and estimates of the operational characteristics are presented.

Lee, K. W.↗
NASA NTRSDate not supplied

Simultaneous Orthogonal Imaging for Cold Flow Characterization of Additively Manufactured Injector Elements

Additively manufactured (AM) injectors have the potential to improve characteristic velocity (C*) performance beyond the 90-97% of theoretical C* performance seen by traditionally manufactured (TM) combustion device injectors. Maximized C* performance yields high overall combustion efficiency in all types of combustion devices, particularly liquid rocket engines (LREs) and rotating detonation rocket engines (RDREs). A high degree of propellant atomization and mixedness is required to achieve maximum C* performance and therefore high overall combustion efficiency. This study focused on measuring and comparing the performance of different novel AM injector elements over a broad range of operating conditions under high pressure, cold flow. As part of this work, a high pressure, cold flow experimental spray facility was designed to measure each element’s injector spray patterns under pressures ranging from 50 to 1000 psig and stiffness ratios from 0.5 to 2.0. Preliminary results are presented from orthogonal, simultaneous imaging comparing atomization and spray geometry between quad, trio, pentad, slotted, and triplet impingers in gas-liquid flow.

Ari D Goldman↗
NASA NTRS2007

Comparison of the Atomic Oxygen Erosion Depth and Cone Height of Various Materials at Hyperthermal Energy

Atomic oxygen readily reacts with most spacecraft polymer materials exposed to the low Earth orbital (LEO) environment. If the atomic oxygen arrival comes from a fixed angle of impact, the resulting erosion will foster the development of a change in surface morphology as material thickness decreases. Hydrocarbon and halopolymer materials, as well as graphite, are easily oxidized and textured by directed atomic oxygen in LEO at energies of approx.4.5 eV. What has been curious is that the ratio of cone height to erosion depth is quite different for different materials. The formation of cones under fixed direction atomic oxygen attack may contribute to a reduction in material tensile strength in excess of that which would occur if the cone height to erosion depth ratio was very low because of greater opportunities for crack initiation. In an effort to understand how material composition affects the ratio of cone height to erosion depth, an experimental investigation was conducted on 18 different materials exposed to a hyperthermal energy directed atomic oxygen source (approx.70 eV). The materials were first salt-sprayed to provide microscopic local areas that would be protected from atomic oxygen. This allowed erosion depth measurements to be made by scanning microscopy inspection. The polymers were then exposed to atomic oxygen produced by an end Hall ion source that was operated on pure oxygen. Samples were exposed to an atomic oxygen effective fluence of 1.0x10(exp 20) atoms/sq cm based on Kapton H polyimide erosion. The average erosion depth and average cone height were determined using field emission scanning electron microscopy (FESEM). The experimental ratio of average cone height to erosion depth is compared to polymer composition and other properties.

Waters, Deborah L.↗