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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Combustion noise from gas turbine aircraft engines measurement of far-field levels

Combustion noise can be a significant contributor to total aircraft noise. Measurement of combustion noise is made difficult by the fact that both jet noise and combustion noise exhibit broadband spectra and peak in the same frequency range. Since in-flight reduction of jet noise is greater than that of combustion noise, the latter can be a major contributor to the in-flight noise of an aircraft but will be less evident, and more difficult to measure, under static conditions. Several methods for measuring the far-field combustion noise of aircraft engines are discussed in this paper. These methods make it possible to measure combustion noise levels even in situations where other noise sources, such as jet noise, dominate. Measured far-field combustion noise levels for several turbofan engines are presented. These levels were obtained using a method referred to as three-signal coherence, requiring that fluctuating pressures be measured at two locations within the engine core in addition to the far-field noise measurement. Cross-spectra are used to separate the far-field combustion noise from far-field noise due to other sources. Spectra and directivities are presented. Comparisons with existing combustion noise predictions are made.

Krejsa, Eugene A.↗
NASA NTRS1993

Simulation of preburner sprays, volume 1

Under the present contract a study was made on the characteristics of the sprays of coaxial injectors with particular emphasis on those aspects relevant to the performance of rocket engines. The technical effort was performed primarily by Imperial College of Science and Technology and the details of this effort are contained in the accompanying technical report by Hardalupas and Whitelaw, which forms Vol. 2 of the report. The role of Scientific Research Associates was review of material, initial direction of the technical effort and review of all reports. The study considered characteristics of sprays under a variety of conditions. Control of these sprays is important as the spray details can control both rocket combustion stability and efficiency. Imperial College considered the following: first, measurement of the size and rate of spread of the sprays produced by single coaxial airblast nozzles with axial gaseous stream. The local size, velocity and flux characteristics for a wide range of gas and liquid flowrates were measured and the results were correlated with the conditions of the spray at the nozzle exit. Second, examination of the effect of the geometry of single coaxial airblast atomizers on spray characteristics. The gas and liquid tube diameters were varied over a range of values, the liquid tube recess was varied and the shape of the exit of the gaseous jet was varied from straight to converging. Third, quantification of the effect of swirl in the gaseous stream on the spray characteristics produced by single coaxial airblast nozzles. Fourth, quantification of the effect of reatomization by impingement of the spray on a flat disc positioned around 200 mm from the nozzle exit. This models spray impingement on the turbopump dome during the startup process of the preburner of the Space Shuttle Main Engine (SSME). Fifth, study of the interaction between multiple sprays without and with swirl in their gaseous stream. The spray characteristics of single nozzles were compared with that of three identical nozzles with their axis at a small distance from each other. This study simulates the sprays in the preburner of the SSME, where there are around 260 elements on the faceplate of the combustion chamber. And lastly, design an experimental facility to study the characteristics of sprays at high pressure conditions and at supercritical pressure and temperature for the gas but supercritical pressure and subcritical temperature for the liquid.

Source record↗
DOE OSTI2022

Phase Contrast X‐Ray Imaging of the Collapse of an Engineered Void in Single‐Crystal HMX

Abstract Imaging the collapse of a single void that creates a hot spot initiation site in an otherwise defect‐free explosive is challenging given the spatial and temporal scales involved in explosive systems. This work presents our attempt to examine a single hot spot mode (void collapse) in single‐crystal octahydro‐l,3,5,7‐tetranitro‐l,3,5,7‐tetrazocine (HMX) embedded in Sylgard. The hot spot heating mechanisms involved with pore collapse include adiabatic heating, jetting, and viscoplastic dissipation. Quantifying the dynamics of a pore collapse is a crucial step to understanding which mechanisms dominate during ignition events. Our experiments were conducted with a single‐stage, light‐gas gun at Argonne National Laboratory's Advanced Photon Source, applying the phase contrast imaging technique while collecting high‐speed video. The details of HMX single crystal production, defect (pore) engineering, and sample construction, along with experimental results are presented here. These results demonstrate that detailed collapse dynamics can be obtained from homogeneous, single‐crystal explosives with this approach. Qualitative comparisons are made with simulation data which show good agreement in the transition between a quasi‐symmetric pore collapse and an asymmetric collapse with jetting across the pore as measured with normalized pore area and pore circularity.

42 ENGINEERING↗
NASA NTRS2006

Laboratory Spectroscopy of Large Carbon Molecules and Ions in Support of Space Missions. A New Generation of Laboratory & Space Studies

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. A long-standing and major challenge for laboratory astrophysics has been to measure the spectra of large carbon molecules in laboratory environments that mimic (in a realistic way) the physical conditions that are associated with the interstellar emission and absorption regions [1]. This objective has been identified as one of the critical Laboratory Astrophysics objectives to optimize the data return from space missions [2]. An extensive laboratory program has been developed to assess the properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space. We present and discuss the gas-phase electronic absorption spectra of neutral and ionized PAHs measured in the UV-Visible-NIR range in astrophysically relevant environments and discuss the implications for astrophysics [1]. The harsh physical conditions of the interstellar medium characterized by a low temperature, an absence of collisions and strong VUV radiation fields - have been simulated in the laboratory by associating a pulsed cavity ringdown spectrometer (CRDS) with a supersonic slit jet seeded with PAHs and an ionizing, penning-type, electronic discharge. We have measured for the {\it first time} the spectra of a series of neutral [3,4] and ionized [5,6] interstellar PAHs analogs in the laboratory. An effort has also been attempted to quantify the mechanisms of ion and carbon nanoparticles production in the free jet expansion and to model our simulation of the diffuse interstellar medium in the laboratory [7]. These experiments provide {\it unique} information on the spectra of free, large carbon-containing molecules and ions in the gas phase. We are now, for the first time, in the position to directly compare laboratory spectral data on free, cold, PAH ions and carbon nano-sized carbon particles with astronomical observations in the UV-NIR range (interstellar UV extinction, DIBs in the NUV-NIR range). This new phase offers tremendous opportunities for the data analysis of current and upcoming space missions geared toward the detection of large aromatic systems Le., the "new frontier space missions" (Spitzer, HST, COS, JWST, SOFIA,...).

Salama, Farid↗
NASA NTRS2002

An Investigation of Applications for Thermodynamic Work Potential Methods: Working Tables and Charts for Estimation of Thermodynamic Work Potential in Equilibrium Mixtures of Jet-A and Air

The objective of this report is to provide a tool to facilitate the application of thermodynamic work potential methods to aircraft and engine analysis. This starts with a discussion of the theoretical background underlying these methods, which is then used to derive various equations useful for thermodynamic analysis of aircraft engines. The work potential analysis method is implemented in the form of a set of working charts and tables that can be used to graphically evaluate work potential stored in high-enthalpy gas. The range of validity for these tables is 300 to 36,000 R, pressures between between 0.01 atm and 100 atm, and fuel-air ratios from zero to stoichiometric. The derivations and charts assume mixtures of Jet-A and air as the working fluid. The thermodynamic properties presented in these charts were calculated based upon standard thermodynamic curve fits.

Mavris, Dimitri↗
NASA NTRS2000

Non-Intrusive, Laser-Based Imaging of Jet-A Fuel Injection and Combustion Species in High Pressure, Subsonic Flows

The emphasis of combustion research efforts at NASA Glenn Research Center (GRC) is on collaborating with industry to design and test gas-turbine combustors and subcomponents for both sub- and supersonic applications. These next-generation aircraft combustors are required to meet strict international environmental restrictions limiting emissions. To meet these goals, innovative combustor concepts require operation at temperatures and pressures far exceeding those of current designs. New and innovative diagnostic tools are necessary to characterize these flow streams since existing methods are inadequate. The combustion diagnostics team at GRC has implemented a suite of highly sensitive, nonintrusive optical imaging methods to diagnose the flowfields of these new engine concepts. By using optically accessible combustors and flame-tubes, imaging of fuel and intermediate combustion species via planar laser-induced fluorescence (PLIF) at realistic pressures are now possible. Direct imaging of the fuel injection process through both planar Mie scattering and PLIF methods is also performed. Additionally, a novel combination of planar fuel fluorescence imaging and computational analysis allows a 3-D examination of the flowfield, resulting in spatially and temporally resolved fuel/air volume distribution maps. These maps provide detailed insight into the fuel injection process at actual conditions, thereby greatly enhancing the evaluation of fuel injector performance and other combustion phenomena. Stable species such as CO2, O2, N2, H2O, and hydrocarbons are also investigated by a newly demonstrated 1-D, spontaneous Raman spectroscopic method. This visible wavelength Raman technique allows the acquisition of quantitative, stable species concentration measurements from the flow.

Locke, R. J.↗
NASA NTRS2001

Non-Intrusive, Laser-Based Imaging of Jet-A Fuel Injection and Combustion Species in High Pressure, Subsonic Flows

The emphasis of combustion research efforts at NASA Glenn Research Center (GRC) is on collaborating with industry to design and test gas-turbine combustors and subcomponents for both sub- and supersonic applications. These next-generation aircraft combustors are required to meet strict international environmental restrictions limiting emissions. To meet these goals, innovative combustor concepts require operation at temperatures and pressures far exceeding those of cur-rent designs. New and innovative diagnostic tools are necessary to characterize these flow streams since existing methods are inadequate. The combustion diagnostics team at GRC has implemented a suite of highly sensitive, nonintrusive optical imaging methods to diagnose the flowfields of these new engine concepts. By using optically accessible combustors and flametubes, imaging of fuel and intermediate combustion species via planar laser-induced fluorescence (PLIF) at realistic pressures are now possible. Direct imaging of the fuel injection process through both planar Mie scattering and PLIF methods is also performed. Additionally, a novel combination of planar fuel fluorescence imaging and computational analysis allows a 3-D examination of the flowfield, resulting in spatially and temporally resolved fuel/air volume distribution maps. These maps provide detailed insight into the fuel injection process at actual conditions, thereby greatly enhancing the evaluation of fuel injector performance and other combustion phenomena. Stable species such as CO2, O2, N2O. and hydrocarbons are also investigated by a newly demonstrated 1-D, spontaneous Raman spectroscopic method. This visible wavelength Raman technique allows the acquisition of quantitative. stable species concentration measurements from the flow.

Locke, Randy J.↗
NASA NTRS2015

A Fully Non-Metallic Gas Turbine Engine Enabled by Additive Manufacturing

The Non-Metallic Gas Turbine Engine project, funded by NASA Aeronautics Research Institute, represents the first comprehensive evaluation of emerging materials and manufacturing technologies that will enable fully nonmetallic gas turbine engines. This will be achieved by assessing the feasibility of using additive manufacturing technologies to fabricate polymer matrix composite and ceramic matrix composite turbine engine components. The benefits include: 50 weight reduction compared to metallic parts, reduced manufacturing costs, reduced part count and rapid design iterations. Two high payoff metallic components have been identified for replacement with PMCs and will be fabricated using fused deposition modeling (FDM) with high temperature polymer filaments. The CMC effort uses a binder jet process to fabricate silicon carbide test coupons and demonstration articles. Microstructural analysis and mechanical testing will be conducted on the PMC and CMC materials. System studies will assess the benefits of fully nonmetallic gas turbine engine in terms of fuel burn, emissions, reduction of part count, and cost. The research project includes a multidisciplinary, multiorganization NASA - industry team that includes experts in ceramic materials and CMCs, polymers and PMCs, structural engineering, additive manufacturing, engine design and analysis, and system analysis.

Ceramics↗
NASA NTRS1998

Algorithm for Estimating the Plume Centerline Temperature and Ceiling Jet Temperature in the Presence of a Hot Upper Layer

The experiments were designed to provide insight into the behavior of jet fuel fires in aircraft hangars and to study the impact of these fires on the design and operation of a variety of fire protection systems. As a result, the test series included small fires designed to investigate the operation of UV/IR detectors and smoke detectors as well as large fires which were used to investigate the operation of ceiling mounted heat detectors and sprinklers. The impact of the presence or absence of draft curtains was also studied in the 15 m hangar. It is shown that in order to predict the plume centerline temperature within experimental uncertainty, the entrainment of the upper layer gas must be modeled. For large fires, the impact of a changing radiation fraction must also be included in the calculation. The dependence of the radial temperature profile of the ceiling jet as a function of layer development is demonstrated and a ceiling jet temperature algorithm which includes the impact of a growing layer is developed.

ALGORITHMS↗
DOE OSTI2021

Tuning plasma parameters to control reactive species fluxes to substrates in the context of plasma catalysis

The key reactive plasma-produced gas phase species responsible for the enhanced conversion of chemicals in plasma catalysis compared to thermal catalysis have to date not been identified. This outstanding question is mainly due to the inherent large variety of plasma-produced species and the challenge of controlling and measuring the flux of each constituent of the cocktail of reactive species to a (catalytic) substrate. In this paper, we explore the possibility to control the dominant reactive species fluxes, relevant for plasma-catalysis, to a substrate in the effluent of an RF driven Ar-O 2 plasma jet. The absolute species densities of the major reactive species (O, O 2 (a 1 Δ g ), O 3 and ions) were quantified by molecular beam mass spectrometry (MBMS) to assess the possibility of using treatment distance, O 2 admixture concentration, plasma dissipated power, RF modulation frequency and duty cycle as well as the feed gas flow rate to alter the dominant species densities. Selected experimental results were also compared with a pseudo-1D plug flow model. The short-lived and long-lived species can be effectively separated by changing the treatment distance and the RF modulation frequency. Furthermore, adjusting the O 2 admixture concentration enables to change the ratio of the O 2 (a 1 Δ g ) and O 3 density. The changes in the trend of ion and O flux were found to be very similar for nearly all investigated parameters. Nonetheless the gas flow rate was able to significantly change the ratio of the O and ion density in the plasma jet effluent. Here, the impact of the surface-dependent loss probability and boundary layer reactions on the species flux to a substrate and how this qualitatively relates to the MBMS density measurements is further addressed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2004

Time-Average Molecular Rayleigh Scattering Technique for Measurement of Velocity, Denisty, Temperature, and Turbulence Intensity in High Speed Nozzle Flows

A molecular Rayleigh scattering based flow diagnostic is developed to measure time average velocity, density, temperature, and turbulence intensity in a 25.4-mm diameter nozzle free jet facility. The spectrum of the Rayleigh scattered light is analyzed using a Fabry-Perot interferometer operated in the static imaging mode. The resulting fringe pattern containing spectral information of the scattered light is recorded using a low noise CCD camera. Nonlinear least squares analysis of the fringe pattern using a kinetic theory model of the Rayleigh scattered light provides estimates of density, velocity, temperature, and turbulence intensity of the gas flow. Resulting flow parameter estimates are presented for an axial scan of subsonic flow at Mach 0.95 for comparison with previously acquired pitot tube data, and axial scans of supersonic flow in an underexpanded screeching jet. The issues related to obtaining accurate turbulence intensity measurements using this technique are discussed.

Mielke, Amy F.↗
DOE OSTI2025

Mixing-Controlled Combustion of Ethanol Enabled by Prechamber Ignition (PC-MCC): A Preliminary Experimental Demonstration

This experimental study presents preliminary investigations of prechamber-enabled mixing-controlled combustion (PC-MCC) at −2 bar brake mean effective pressure (BMEP) and 2200 rpm with fuel-grade ethanol (E98). Experimental results are conducted on a prechamber retrofitted single-cylinder Caterpillar C9.3B test engine. First, a series of prechamber-only experiments were conducted with a motored engine to evaluate the salient combustion trends in response to relevant prechamber operating parameters. Under firing conditions, the prechamber operating strategy was assessed with respect to the impact on ignition assistance of direct-injected E98 and overall engine performance. The preliminary results indicate the jet-induced ignition process is robust and prompts diffusion combustion of E98 at diesel-like boundary conditions. Here, the effect of external exhaust gas recirculation (EGR) on the residual tolerance of the prechamber combustion process was also investigated and showed stable combustion in both the main chamber and prechamber up to 30% EGR. Experiments were also conducted with the stock diesel engine for baseline comparison. At matched combustion phasing, mixing-controlled combustion of ethanol enabled by prechamber ignition was able to achieve heightened gross thermal efficiency while simultaneously reducing NOx and practically eliminating smoke emissions relative to diesel combustion. In addition, the covariance of load and standard deviation of combustion phasing was diesel-like and less than 2% and 1 CAD, respectively.

PC-MCC↗
NASA NTRS1980

Fuel property effects in stirred combustors

Soot formation in strongly backmixed combustion was investigated using the jet-stirred combustor (JSC). This device provided a combustion volume in which temperature and combustion were uniform. It simulated the recirculating characteristics of the gas turbine primary zone; it was in this zone where mixture conditions were sufficiently rich to produce soot. Results indicate that the JSC allows study of soot formation in an aerodynamic situation revelant to gas turbines.

Source record↗
NASA NTRS1994

Shocked molecular gas around the extremely young source IRAS 03282+3035

We present observations of the shock tracers H2 and SiO around the young stellar object IRAS 03282+3035. This unusual low-luminosity (L approximately = 2 solar luminosity) source drives a strong highly collimated CO outflow, and it is one of the youngest stellar objects known so far. The near-infrared H2 emission, tracing 2000 K gas, comes from extremely high velocity CO bullets along the axis of the blueshifted lobe of the outflow. The millimeter SiO emission, tracing roughly 100 K gas, arises from lower velocity material at the end of the outflow lobe. The lack of high-temperature and high-velocity gas at the end of the outflow lobe indicates there is no not bow shock at the outflow termination. In the context of current jet models this appears to rule out a bow shock driven by a steady state jet. Possible explanations for the structure include a time-dependent jet or a jet dominated by turbulent entrainment.

Bachiller, R.↗
NASA NTRS1996

NASA flow fields analysis

The objectives of the present research are to improve design capabilities for low thrust rocket engines through understanding the detailed mixing and combustion processes in a representative combustor. Of particular interest is a small gaseous hydrogen-oxygen thruster which is considered as a coordinated part of an on-going experimental program at NASA LERC. Detailed computational modeling involves the solution of both the two- and three-dimensional Navier Stokes equations, coupled with chemical reactions and the species diffusion equations. Computations of interest include both steady state and time-accurate flowfields and are obtained by means of LU approximate factorization in time and flux split upwinding differencing in space. The emphasis in the research is focused on using numerical analysis to understand detailed combustor flowfields, including the shear layer dynamics created between fuel film cooling and the core gas in the vicinity on the nearby combustor wall; the integrity and effectiveness of the coolant film; and three-dimensional fuel and oxidizer jet injection/mixing/combustion characteristics in the primary combustor along with their joint impacts on global engine performance.

Merkle, Charles L.↗
NASA NTRS1998

Injector Design Tool Improvements: User's manual for FDNS V.4.5

The major emphasis of the current effort is in the development and validation of an efficient parallel machine computational model, based on the FDNS code, to analyze the fluid dynamics of a wide variety of liquid jet configurations for general liquid rocket engine injection system applications. This model includes physical models for droplet atomization, breakup/coalescence, evaporation, turbulence mixing and gas-phase combustion. Benchmark validation cases for liquid rocket engine chamber combustion conditions will be performed for model validation purpose. Test cases may include shear coaxial, swirl coaxial and impinging injection systems with combinations LOXIH2 or LOXISP-1 propellant injector elements used in rocket engine designs. As a final goal of this project, a well tested parallel CFD performance methodology together with a user's operation description in a final technical report will be reported at the end of the proposed research effort.

Chen, Yen-Sen↗