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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Deterrent Concentration Measurement with FTIR and Subsequent Ballistic Performance in Medium Caliber Propellant

To meet ballistic requirements, medium and small caliber propellants use deterrent coatings to obtain burn rate progressivity. The required amount and distribution of deterrent varies between gun systems, propellant types, and often between lots. Micro Fourier Transform Infrared (FTIR) spectroscopy was used to measure deterrent gradients in RP36 propellants coated with methyl centralite (MC) at different deterrent levels and different processing conditions. The aromatic C-C bonds at 1496 cm(exp -1) wavenumber were used to monitor the deterrent profiles through the grain. Deterrent gradients measured with FTIR spectroscopy were then used to estimate burn rate gradients in the deterred grains. Burn rates were calculated from literature models and from closed bomb data of RP36 containing uniform deterrent concentration. Finally, the burn rate gradients were input into an IBHFG2 model of a 200 cc-closed bomb. The early flame spreading portion of the closed bomb ballistic cycle (0 to 0.2 P/Pmax) was roughly modeled by dividing the charge up into five propellant decks and igniting them at different times in the ballistic cycle. Pressure traces and vivacity curves from closed bomb shots were compared to predictions. In addition to the burn rate gradient, the closed bomb pressure trace was heavily dependent on ignition and flame spread. These two phenomena were not readily distinguishable from one another in deterred grains. The same RP-36 propellant was shot in a 25 mm M793TP round which was again modeled with IBHVG2. Peak pressure and muzzle velocity were accurately modeled when erosive burning effects were empirically factored into the model.

Furrow, Keith W.↗
NASA NTRS1999

Preliminary Results of the Third Test Series of Nonmetal Material Flammability Evaluation In SKOROST Apparatus on the Space Station Mir

The work has been done according to the US/Russian Joint Project "Experimental Evaluation of the Material Flammability in Microgravity" a continued combustion study in the SKOROST test apparatus on the OS Mir. The objective of the project was to evaluate the flammability and flame-spread rate for the selected polymer materials in low velocity flow in microgravity. Lately, the issue of nonmetal material combustion in microgravity has become of great importance, based on the necessity to develop the fire safety system for the new International Space Station (ISS). Lack of buoyant flow in microgravity reduces oxygen transfer into the combustion zone, which leads to flame extinction when the flow velocity is less than the limiting flow velocity V(sub lim) for the material. The ISS FGB fire-safety system was developed based on this phenomenon. The existence of minimum flow velocity V(sub lim) to sustain fire for the selected materials was determined both theoretically and experimentally. In the latter, it is shown that, even for thermally thin nonmetal materials with a very low oxygen index C(sub lim) of 12.5% (paper sheets with the thickness of 0.1 mm), a limiting flow velocity V(sub lim) exists at oxygen concentration Co(sub OX) = 17-21%, and is about 1.0 - 0.1 cm/sec. This might be explained by the relative increase in thermal losses due to radiation from the surface and from the gaseous phase. In the second series of experiments in Skorost apparatus on Orbital Station Mir the existence of the limiting flow velocity V(sub lim) for combustion was confirmed for PMMA and glass-epoxy composite strip samples 2 mm thick at oxygen concentration C(sub OX) = 21.5%. It was concluded that V(sub lim) depends on C(sub OX) for the PMMA sample with a low oxygen index of 15.5%, the limiting flow velocity V(sub lim) was less than 0.5 cm/sec, and for the glass-epoxy composite sample with a high oxygen index of 19%, the limiting flow velocity V(sub lim) was higher than 15 cm/sec. As of now only those materials that maintain their integrity during combustion were investigated. The materials that disintegrate when burning present more danger for fire safety because the flame can spread farther with the parts of the structure, ejected melt drops, et cetera. Materials such as polyethylene are of great interest since they form a lengthy melt zone during the combustion in normal gravity. This melt zone generates drops of liquids that promote faster flame spread compared to usual combustion. The preliminary results of polyethylene insulation flammability evaluation in microgravity are shown in the NASA Wire Insulation Flammability (WIF) experiment during Space Shuttle flight STS-50. A lot of interesting data was collected during the WIF test program. However, one of the most important results was that, in microgravity, the extinction of the polyethylene occurred almost immediately when the flow of relatively low oxygen concentration (C(sub OX)=21%) was stopped. The purpose of the work reported here is to expand the existing data base on material flammability in microgravity and to conduct the third series of the space experiment using Skorost apparatus on Orbiatl Station Mir with melting polymers, which might increase the probability of fire and its propagation in ventilated microgravity environment of orbiting spacecraft.

Ivanov, A. V.↗
NASA NTRS1988

Spacecraft Fire-Safety Experiments for Space Station: Technology Development Mission

Definitions, overall descriptions, and preliminary apparatus and instrumentation requirements are presented for three spacecraft fire-safety experiments appropriate for inclusion in a growth-version of the Space Station. The experiments are as follows: 1. Combustion and Flame Spread of Typical Spacecraft Materials in a Low­ Velocity Convective Flow in Low Gravity 2. Fire and Fire-Extinguishant Interactions with Various Fire Scenarios in Low Gravity 3. Smoldering and Deep-Seated Combustion in Low Gravity. The experiments were selected from an assessment of recommendations for advanced technologies for prevention, detection, and control of fires in spacecraft. The experiments and their facilities are intended to constitute a portion of a Spacecraft Fire Safety Technology Development Mission (TDM). Basic requirements for the mission study are that the Space Station is essential for the accomplishment of the experimental objectives and that the technology being developed is appropriate for the growth version of the Space Station. The advantages of these three experiments are that, not only do they explore problems relevant to the Space Station operation and utilization, but also they constitute tests adaptable to two multiuse facilities installed in the Space Station laboratory module, the Combustion Tunnel Facility and the Combustion Facility. Three additional spacecraft fire-safety experiments, essential precursors to the TD M for near-term performance, are also described as follows: 1. Near-Term Testing of Materials for Combustion and Flame Spread 2. Near-Term Extinguishment of Fires in a Low-Gravity Test Bed 3. Post-Fire Recovery of Sensitive Electrical and Electronic Equipment. For all the experiments, the study defines accommodations in terms of first-order space, mass, power, consumables, and crew-time estimates. The study also reviews the key problems to be addressed, namely experiment safety hazards, non-intrusive diagnostics development and waste-products disposal. A preliminary task and time schedule for design, development, and experiment fabrication is proposed.

Youngblood, Wallace W.↗
NASA NTRS1984

Photovoltaic module spread-of-flame testing

Photovoltaic modules used in solar energy conversion are tested for flammability. Class B burning brand tests were conducted with the following results: module glass shattered and hydrocarbon encapsulants ignited. Penetration of back surface material was the prime cause of failure. Materials with greater flame and heat resistance are under consideration to increase back surface integrity up to Class A burning brand standard. The most promising is stainless steel foil.

Sugimura, R. S.↗
NASA NTRS1995

Radiant extinction of gaseous diffusion flames

The absence of buoyancy-induced flows in microgravity significantly alters the fundamentals of many combustion processes. Substantial differences between normal-gravity and microgravity flames have been reported during droplet combustion, flame spread over solids, candle flames, and others. These differences are more basic than just in the visible flame shape. Longer residence time and higher concentration of combustion products create a thermochemical environment which changes the flame chemistry. Processes such as flame radiation, that are often ignored under normal gravity, become very important and sometimes even controlling. This is particularly true for conditions at extinction of a microgravity diffusion flame. Under normal-gravity, the buoyant flow, which may be characterized by the strain rate, assists the diffusion process to transport the fuel and oxidizer to the combustion zone and remove the hot combustion products from it. These are essential functions for the survival of the flame which needs fuel and oxidizer. Thus, as the strain rate is increased, the diffusion flame which is 'weak' (reduced burning rate per unit flame area) at low strain rates is initially 'strengthened' and eventually it may be 'blown-out'. Most of the previous research on diffusion flame extinction has been conducted at the high strain rate 'blow-off' limit. The literature substantially lacks information on low strain rate, radiation-induced, extinction of diffusion flames. At the low strain rates encountered in microgravity, flame radiation is enhanced due to: (1) build-up of combustion products in the flame zone which increases the gas radiation, and (2) low strain rates provide sufficient residence time for substantial amounts of soot to form which further increases the flame radiation. It is expected that this radiative heat loss will extinguish the already 'weak' diffusion flame under certain conditions. Identifying these conditions (ambient atmosphere, fuel flow rate, fuel type, etc.) is important for spacecraft fire safety. Thus, the objective is to experimentally and theoretically investigate the radiation-induced extinction of diffusion flames in microgravity and determine the effect of flame radiation on the 'weak' microgravity diffusion flame.

Atreya, Arvind↗
NASA NTRS2001

Spread Across Liquids Continues to Fly

The physics and behavior of a flame spreading across a flammable liquid is an active area of research at the NASA Glenn Research Center. Spills of fuels and other liquids often result in considerable fire hazards, and much remains unknown about the details of how a flame, once ignited, moves across a pool. The depth of the liquid or size of the spill, the temperature, and wind, if any, can all complicate the combustion processes. In addition, with the advent of the International Space Station there may be fire hazards associated with cleaning, laboratory, or other fluids in space, and it is essential to understand the role that gravity plays in such situations. The Spread Across Liquids (SAL) experiment is an experimental and computational effort dedicated to understanding the detailed mechanisms of flame spread across a flammable liquid initially below its flashpoint temperature. The experimental research is being carried out in-house by a team of researchers from Glenn, the National Center for Microgravity Combustion, and Zin Technologies, with computer modeling being provided via a grant with the University of California, Irvine. Glenn's Zero Gravity Facility is used to achieve short microgravity periods, and normal gravity testing is done in the Space Experiments Laboratory. To achieve longer periods of microgravity, the showcase SAL hardware flies aboard a sounding rocket launched from White Sands Missile Range, New Mexico, approximately once per year. In addition to extended microgravity, this carrier allows the use of detailed diagnostics that cannot be employed in a drop tower.

Miller, Fletcher J.↗
NASA NTRS1999

Reflight of the Solid Surface Combustion Experiment: Flame Radiation Near Extinction

In flame spreading in quiescent and low-velocity opposing flows, effects of surface reradiation and flame radiation are important in establishing the spread rate and whether the flame, once ignited, survives to steady spread or extinguishes after a time long compared to the ignition event. A reflight of the Solid Surface Combustion Experiment (SSCE), supported by modelling, demonstrates that for thick, flat fuels, the ultimate fate of the flame is extinction rather than steady spread. A mismatch between the thermal scale in the gas, driven by radiation, and the species diffusion scale, driven by mass diffusion, develops such that the high temperature regions of the flame are ultimately located in a region to which oxygen cannot be supplied at a sufficient rate to sustain reaction, and extinction occurs. Results of the experiment conducted on Space Shuttle mission STS 85 on 9 August 1997 are reviewed. For the flat surface geometry, while the hydrodynamic phenomena associated with opposed-flow flame spread may be treated two dimensionally, the radiative effects are three dimensional, and so modelling the radiative processes, with the mismatch in dimensionality, is difficult. The cylindrical geometry at least one long compared to the radius, provides a configuration in which the radiative processes for spread in the axial direction are two dimensional, thus simplifying the modelling. The cylindrical geometry allows for the development of more sophisticated radiative models without the complication of dimensionality concerns, e.g., discrete transfer, which is discussed in detail by Bundy (1998). Additionally, the cylindrical geometry results in a "focussing" of the heat transfer to the surface and may allow for steady spread for radii that for thick fuels of the same half-thickness there is no steady spread.

Altenkirch, R. A.↗
DOE OSTI2021

Two-color pyrometry based flame to fuel surface radiative heat flux diagnostic using flamelets

In this study, a non-intrusive two-color pyrometry based radiative heat flux diagnostic is presented that accounts for the self-absorption effects. This diagnostic relies on looking up the flame temperature and soot volume fraction using the ratio of color intensities obtained from digital cameras and numerical solutions of 1D steady-state diffusion flames. Virtual two color pyrometry of computed flame show a unique one-to-one mapping of strained flames with intensity ratio; thereby allowing flames to be indexed and creation of a two-color flamelet manifold (TCFM). The TCFM is a function of two variables; the ratio of red to green intensities (flame index) and physical distance to the stoichiometric surface defined using a level-set function. The developed diagnostic is used in upward flame spread experiments where an approximate flame hull reconstruction method is applied to provide the 3D level-set function and intensity ratio for use of TCFM to provide radiative absorption properties for 3D ray tracing. Accounting for self- absorption effects provide improved soot volume fraction estimates. In conclusion, the radiative heat flux estimates are found to be in very good agreement with literature and improved results are obtained near the flame base.

42 ENGINEERING↗
NASA NTRS1997

SAMS Acceleration Measurement on Mir From March to September 1996

During NASA Increment 2 (March to September 1996), over 15 gigabytes of acceleration data were collected by the Space Acceleration Measurement System (SAMS) onboard the Russian Space Station, Mir. The data were recorded on 55 optical disks and were returned to Earth on STS-79. During this time, SAMS data were collected in the Kristall and Kvant modules, and in the Priroda module to support the following experiments: the Queen's University Experiments in Liquid Diffusion (QUELD), the Technological Evaluation of the MIM (TEM), the Forced Flow Flame Spreading Test (FFFT), and Candle Flames in Microgravity (CFM). This report points out some of the salient features of the microgravity environment to which these experiments were exposed. Also documented are mission events of interest such as the docked phase of STS-76 operations, an extravehicular activity (EVA) to install and deploy solar panels on the Kvant module, a Progress engine burn to raise Mir's altitude, and an on-orbit SAMS calibration procedure. Also included are a description of the Mir module orientations, and the panel notations within the modules. This report presents an overview of the SAMS acceleration measurements recorded by 10 Hz and 100 Hz sensor heads. Variations in the acceleration environment caused by unique activities such as crew exercise and life-support fans are presented. The analyses included herein complement those presented in previous mission summary reports published by the Principal Investigator Microgravity Services (PIMS) group.

Moskowitz, Milton E.↗
NASA NTRS2006

Signature of Temporary Burning Front Stalling from a Non-Photospheric Radius Expansion Double-Peaked Burst

Non-photospheric-radius-expansion(non-PRE) double-peaked bursts may be explained in terms of spreading (and temporary stalling) of thermonuclear flames on the neutron star surface, as we argued in a previous study of a burst assuming polar ignition. Here we analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of such a burst (but with a considerably different intensity profile from the previous one) from the low mass X-ray binary (LMXB) system 4U 1636-536, and show that this model can qualitatively explain the observed burst profile and spectral evolution, if we assume an off-polar, but high-latitude ignition, and burning front stalling at a higher latitude compared to that for the previous burst. The off-polar ignition can account for the millisecond period brightness oscillations detected from this burst. This is the first time oscillations have been seen from such a burst. Our model can qualitatively explain the oscillation amplitude measured during the first (weaker) peak, and the absence of oscillations during the second peak. The higher latitude front stalling facilitates the first clear detection of a signature of this stalling, which is the primary result of this work, and may be useful for understanding thermonuclear flame spreading on neutron stars.

Bhattacharyya, Sudip↗
NASA NTRS2003

Flamelet Formation In Hele-Shaw Flow

A Hele-Shaw flow apparatus constructed at Michigan State University (MSU) produces conditions that reduce influences of buoyancy-driven flows. In addition, in the MSU Hele-Shaw apparatus it is possible to adjust the heat losses from the fuel sample (0.001 in. thick cellulose) and the flow speed of the approaching oxidizer flow (air) so that the "flamelet regime of flame spread" is entered. In this regime various features of the flame-to-smolder (and vice versa) transition can be studied. For the relatively wide (approx. 17.5 cm) and long (approx. 20 cm) samples used, approximately ten flamelets existed at all times. The flamelet behavior was studied mechanistically and statistically. A heat transfer analysis of the dominant heat transfer mechanisms was conducted. Results indicate that radiation and conduction processes are important, and that a simple 1-D model using the Broido-Shafizadeh model for cellulose decomposition chemistry can describe aspects of the flamelet spread process. Introduction

Wichman, I. S.↗
NASA NTRS1999

A Theory of Oscillating Edge Flames

It has been known for some years that when a near-limit flame spreads over a liquid pool of fuel, the edge of the flame can oscillate relative to a frame moving with the mean speed. Each period of oscillation is characterized by long intervals of modest motion during which the edge gases radiate like those of a diffusion flame, punctuated by bursts of rapid advance during which the edge gases radiate like those in a deflagration. Substantial resources have been brought to bear on this issue within the microgravity program, both experimental and numerical. It is also known that when a near-asphyxiated candle-flame burns at zero gravity, the edge of the (hemispherical) flame can oscillate violently prior to extinction. Thus a web-surfer, turning to the NASA web-site at http://microgravity.msfc.nasa.gov, and following the trail combustion science/experiments/experimental results/candle flame, will find photographs and a description of candle burning experiments carried out on board both the Space-shuttle and the Russian space station Mir. A brief report can also be found in the proceedings of the Fourth Workshop. And recently, in a third microgravity program, the leading edge of the flame supported by injection of ethane through the porous surface of a plate over which air is blown has been found to oscillate when conditions are close to blow-off. A number of important points can be made with respect to these observations: It is the edge itself which oscillates, advancing and retreating, not the diffusion flame that trails behind the edge; oscillations only occur under near limit conditions; in each case the Lewis number of the fuel is significantly larger than 1; and because of the edge curvature, the heat losses from the reacting edge structure are larger than those from the trailing diffusion flame. We propose a general theory for these oscillations, invoking Occam's 'Law of Parsimony' in an expanded form, to wit: The same mechanism is responsible for the oscillations in all three experiments; and no new mechanism is invoked (Occam's original 'Razor'). Such a strategy eliminates Marangoni effects as the source, for these are absent in the second and third experiments. And it eliminates arguments that point to numerically predicted gas eddies as the source, a new mechanism, unelucidated. Indeed, we hypothesize that the essential driving mechanism for the instability is a combination of large Lewis number and heat losses from the reacting structure near the flame edge. Instabilities driven by these mechanisms are commonplace in 1D configurations. Chemical reactor theory, for example, leads to system responses which mimic the response of the candle flame - steady flame, oscillations, extinction. In a combustion context, oscillating instabilities were first reported for diffusion flames in a theoretical study by Kirkby and Schmitz, and here also the instabilities are associated with near-extinction conditions, large Lewis numbers, and heat losses. And deflagrations will oscillate if the Lewis number is large enough, oscillations that are exacerbated when heat losses are present, whether global or to a surface.

Buckmaster, J.↗
NASA NTRS1999

Gravitational Influences on Flame Propagation Through Non-Uniform Premixed Gas Systems

Flame propagation through non-uniformly premixed gases occurs in several common combustion situations. As summarized in a previous conference paper, non-uniform premixed gas combustion has received scant attention compared to the more usual limiting cases of diffusion or uniformly premixed flames. It is the goal of this research to further our knowledge of layered combustion, in which a fuel concentration gradient exists normal to the direction of flame spread, in particular by focusing on the role that gravity plays. Gravity can affect flame propagation in at least three ways: through a hydrostatic pressure gradient, by altering the initial distribution of fuel vapor, and through buoyantly induced flows once ignition has occurred. An understanding of the phenomena involved is important to fire safety, especially aboard spacecraft since no microgravity data exist. The data obtained will also be useful to verify theoretical models of this problem, which are easier to implement if buoyancy is neglected.

Miller, Fletcher J.↗
NASA NTRS1995

Interactions between flames on parallel solid surfaces

The interactions between flames spreading over parallel solid sheets of paper are being studied in normal gravity and in microgravity. This geometry is of practical importance since in most heterogeneous combustion systems, the condensed phase is non-continuous and spatially distributed. This spatial distribution can strongly affect burning and/or spread rate. This is due to radiant and diffusive interactions between the surface and the flames above the surfaces. Tests were conducted over a variety of pressures and separation distances to expose the influence of the parallel sheets on oxidizer transport and on radiative feedback.

Urban, David L.↗
NASA NTRS1980

The 17th JANNAF Combustion Meeting, Volume 2

Combustion of gun and nitramine propellants are discussed. Topics include gun charge designs, flame spreading in granular and stick charges, muzzle flash, ignition and combustion of liquid propellants for guns, laminar flames, decomposition and combustion of nitramine ingredients and nitramine propellant development.

Eggleston, D. S.↗
NASA NTRS1997

Radiation Temperature and Extinction of Transient Gaseous Diffusion Flames in Microgravity

The absence of buoyancy-induced flows in micro-g and the resulting increase in the reactant residence time significantly alters the fundamentals of many combustion processes. Substantial differences between 1-g and micro-g flames have been reported in experiments on candle flames, flame spread over solids, droplet combustion and others. These differences are more basic than just in the visible flame shape. Longer residence times and higher concentration of combustion products in the flame zone create a thermochemical environment which changes the flame chemistry and the heat and mass transfer processes. Processes such as flame radiation (and its interaction with flame chemistry), that are often ignored under normal gravity, become very important and sometimes even controlling. This is particularly true for conditions at extinction of a micro-g diffusion flame.

Arvind Atreya↗
NASA NTRS1999

Radiant Extinction of Gaseous Diffusion Flames

The absence of buoyancy-induced flows in microgravity (mu-g) and the resulting increase in the reactant residence time significantly alters the fundamentals of many combustion processes. Substantial differences between normal gravity (ng) and mu-g flames have been reported in experiments on candle flames, flame spread over solids, droplet combustion, and others. These differences are more basic than just in the visible flame shape. Longer residence times and higher concentration of combustion products in the flame zone create a thermochemical environment that changes the flame chemistry and the heat and mass transfer processes. Processes such as flame radiation, that are often ignored in ng, become very important and sometimes even controlling. Furthermore, microgravity conditions considerably enhance flame radiation by: (1) the build-up of combustion products in the high-temperature reaction zone which increases the gas radiation; and (2) longer residence times make conditions appropriate for substantial amounts of soot to form which is also responsible for radiative heat loss. Thus, it is anticipated that radiative heat loss may eventually extinguish the "weak" (low burning rate per unit flame area) mu-g diffusion flame. Yet, space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in mu-g will burn indefinitely. This may be because of the coupling between the fuel production rate and the flame via the heat-feedback mechanism for candle flames, flames over solids and fuel droplet flames. Thus, to focus only on the gas-phase phenomena leading to radiative extinction, aerodynamically stabilized gaseous diffusion flames are examined. This enables independent control of the fuel flow rate to help identify conditions under which radiative extinction occurs. Also, spherical geometry is chosen for the mu-g experiments and modeling because: (1) It reduces the complexity by making the problem one-dimensional; (2) The spherical diffusion flame completely encloses the soot which is formed on the fuel rich side of the reaction zone. This increases the importance of flame radiation because now both soot and gaseous combustion products co-exist inside the high temperature spherical diffusion flame; (3) For small fuel injection velocities, as is usually the case for a pyrolyzing solid, the diffusion flame in mu-g around the solid naturally develops spherical symmetry. Thus, spherical diffusion flames are of interest to fires in mu-g and identifying conditions that lead to radiation-induced extinction is important for spacecraft fire safety.

Berhan, Sean↗
NASA NTRS2000

Cooperative Research Projects in the Microgravity Combustion Science Programs Sponsored by NASA and NEDO

This document contains the results of a collection of selected cooperative research projects between principal investigators in the microgravity combustion science programs, sponsored by NASA and NEDO. Cooperation involved the use of drop towers in Japan and the United States, and the sharing of subsequent research data and findings. The topical areas include: (1) Interacting droplet arrays, (2) high pressure binary fuel sprays, (3) sooting droplet combustion, (4) flammability limits and dynamics of spherical, premixed gaseous flames and, (5) ignition and transition of flame spread across thin solid fuel samples. All of the investigators view this collaboration as a success. Novel flame behaviors were found and later published in archival journals. In some cases the experiments provided verification of the design and behavior in subsequent experiments performed on the Space Shuttle. In other cases, the experiments provided guidance to experiments that are expected to be performed on the International Space Station.

Ross, Howard↗