Engineering topics

Dryer, Frederick L.

Publications and source records attributed to Dryer, Frederick L..

At least 19 records

NASA NTRS2015

Detailed Results from the Flame Extinguishment Experiment (FLEX) March 2009 to December 2011

The Flame Extinguishment Experiment (FLEX) program is a continuing set of experiments on droplet combustion, performed employing the Multi-User Droplet Combustion Apparatus (MDCA), inside the chamber of the Combustion Integrated Rack (CIR), which is located in the Destiny module of the International Space Station (ISS). This report describes the experimental hardware, the diagnostic equipment, the experimental procedures, and the methods of data analysis for FLEX. It also presents the results of the first 284 tests performed. The intent is not to interpret the experimental results but rather to make them available to the entire scientific community for possible future interpretations.

International Space Station↗

NASA NTRS2009

Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment

Multi-User Droplet Combustion Apparatus Flame Extinguishment Experiment (MDCA-FLEX) will assess the effectiveness of fire suppressants in microgravity and quantify the effect of different possible crew exploration atmospheres on fire suppression. The goal of this research is to provide definition and direction for large scale fire suppression tests and selection of the fire suppressant for next generation crew exploration vehicles.

Williams, Forman A.↗

NASA NTRS2003

Experiments And Model Development For The Investigation Of Sooting And Radiation Effects In Microgravity Droplet Combustion

This study involves flight experiments (for droplets between 1.5 to 5 mm) and supportive ground-based experiments, with concurrent numerical model development and validation. The experiments involve two fuels: n-heptane, and ethanol. The diagnostic measurements include light extinction for soot volume fraction, two-wavelength pyrometry and thin-filament pyrometry for temperature, spectral detection for OH chemiluminescence, broadband radiometry for flame emission, and thermophoretic sampling with subsequent transmission electron microscopy for soot aerosol property calculations.

Yozgatligil, Ahmet↗

NASA NTRS2001

Experiments and Model Development for the Investigation of Sooting and Radiation Effects in Microgravity Droplet Combustion

Today, despite efforts to develop and utilize natural gas and renewable energy sources, nearly 97% of the energy used for transportation is derived from combustion of liquid fuels, principally derived from petroleum. While society continues to rely on liquid petroleum-based fuels as a major energy source in spite of their finite supply, it is of paramount importance to maximize the efficiency and minimize the environmental impact of the devices that burn these fuels. The development of improved energy conversion systems, having higher efficiencies and lower emissions, is central to meeting both local and regional air quality standards. This development requires improvements in computational design tools for applied energy conversion systems, which in turn requires more robust sub-model components for combustion chemistry, transport, energy transport (including radiation), and pollutant emissions (soot formation and burnout). The study of isolated droplet burning as a unidimensional, time dependent model diffusion flame system facilitates extensions of these mechanisms to include fuel molecular sizes and pollutants typical of conventional and alternative liquid fuels used in the transportation sector. Because of the simplified geometry, sub-model components from the most detailed to those reduced to sizes compatible for use in multi-dimensional, time dependent applied models can be developed, compared and validated against experimental diffusion flame processes, and tested against one another. Based on observations in microgravity experiments on droplet combustion, it appears that the formation and lingering presence of soot within the fuel-rich region of isolated droplets can modify the burning rate, flame structure and extinction, soot aerosol properties, and the effective thermophysical properties. These observations led to the belief that perhaps one of the most important outstanding contributions of microgravity droplet combustion is the observation that in the absence of asymmetrical forced and natural convection, a soot shell is formed between the droplet surface and the flame, exerting an influence on the droplet combustion response far greater than previously recognized. The effects of soot on droplet burning parameters, including burning rate, soot shell dynamics, flame structure, and extinction phenomena provide significant testing parameters for studying the structure and coupling of soot models with other sub-model components.

Choi, Mun Young↗

NASA NTRS2000

Experimental and Modeling Study of the Burning of an Ethanol Droplet in Microgravity

The microgravity ethanol droplet combustion experiments were performed aboard the STS-94/MSL-1 Shuttle mission within the Fiber-Supported Droplet Combustion-2 (FSDC-2) program. The burning histories and flame standoffs for pure ethanol and ethanol/water droplets were obtained from the images recorded with two 8 mm videocameras. The obtained results show that average gasification rate is related to the initial droplet size in a manner similar to n-alkanes and methanol and consistent with the results of Hara and Kumagai and the data taken recently in the NASA-Lewis 2.2 s droptower. A transient, moving finite-element chemically reacting flow model applied previously to sphero-symmetric combustion of methanol, methanol/water, n-alkane, and n-alkane binary mixture droplets was adopted for the problem of ethanol droplet combustion. The model includes detailed description of gas-phase reaction chemistry and transport, a simplified description of liquid phase transport, and non-luminous radiative heat transfer. Gas-phase chemistry was described with the detailed reaction mechanism of Norton and Dryer, which consists of 142 reversible elementary reactions of 33 species. Another recently published reaction mechanism of high-temperature ethanol oxidation was also considered. The model predictions were found to compare favorably with the experimental data. The model analysis also indicates that water condensation in the case of ethanol has smaller effect on average droplet gasification rate as compared with previously studied methanol cases. This effect is explained by non-ideal (azeotropic) behavior of binary ethanol-water mixtures. Further analysis of computational results and ethanol droplet radiative extinction behavior will be discussed.

Kazakov, Andrei↗

NASA NTRS2000

The Burning of Large N-Heptane Droplets in Microgravity

Experimental results are presented on the burning and sooting behavior of large n-heptane droplets in air at atmospheric pressure under microgravity conditions. The experiments were performed at the Japanese Microgravity Center (JAMIC) 10 sec dropshaft in Hokkaido, Japan. Soot volume fraction, burning rate, flame standoff and luminosity were measured for droplets of 2.6 mm and 2.9 mm in initial diameter. These are the largest droplets for which soot volume fraction measurements have ever been performed. Previous measurements of soot volume fractions for n-heptane droplets, confined to smaller droplet sizes of less than 1.8 mm, indicated that maximum soot volume fraction increased monotonically with initial droplet size. The new results demonstrate for the first time that sooting tendency is reduced for large droplets as it has been speculated previously but never confirmed experimentally. The lower soot volume fractions for the larger droplets were also accompanied by higher burning rates. The observed phenomenon is believed to be caused by the dimensional influence on radiative heat losses from the flame. Numerical calculations confirm that soot radiation affects the droplet burning behavior.

Manzello, Samuel L.↗

NASA NTRS1999

Workshop on Aerosols and Particulates from Aircraft Gas Turbine Engines

This paper reviews the relationships of the programs and projects and reviews the purpose of the Engine Exhaust Trace Chemistry (EETC) Committee. The charges of the Committee are: (1) to prioritize the engine trace constituents for assessing impacts of aircraft; (2) Assess both extractive and insitu measurement techniques; and (3) Determine the best venues for performing the necessary measurements. A synopsis of evidence supporting and questions concerning the role(s) of aerosol/particulates was presented. The presentation also reviewed how sulfur oxidation kinetics interactions in the hot-section and nozzle play a role in the formation of aerosol precursors. The objective of the workshop, and its organization is reviewed.

Niedzwiecki, Richard↗

NASA NTRS1999

Initial Observations on the Burning of an Ethanol Droplet in Microgravity

Combustion of liquid ethanol represents an important system both from fundamental and practical points of view, Ethanol is currently being used as an additive to gasoline in order to reduce carbon monoxide and particulate emissions as well as to improve the fuel octane rating. A detailed physical understanding of liquid ethanol combustion is therefore necessary to achieve an optimal performance of such fuel blends in practical conditions. Ethanol is also a relatively simple model compound suitable for investigation of important combustion characteristics typical of more complex fuels. In particular, ethanol has been proposed for studies of sooting behavior during droplet burning. The sooting nature of ethanol has pressure sensitivities similar to that of n-heptane, but shifted to a higher range of pressures (1-3 atm). Additionally, liquid ethanol is miscible with water produced during its combustion forming mixtures with azeotropic behavior, a phenomenon important for understanding multi-component, liquid fuel combustion. In this work, we present initial results obtained in a series of recent space-based experiments and develop a detailed model describing the burning of ethanol droplet in microgravity.

Kazakov, Andrei↗

NASA NTRS1998

Droplet Combustion Experiment (DCE)

The first space-based experiments were performed on the combustion of free, individual liquid fuel droplets in oxidizing atmospheres. The fuel was heptane, with initial droplet diameters ranging about from 1 mm to 4 mm. The atmospheres were mixtures of helium and oxygen, at pressures of 1.00, 0.50 and 0.25 bar, with oxygen mole fractions between 20% and 40%, as well as normal Spacelab cabin air. The temperatures of the atmospheres and of the initial liquid fuel were nominally 300 K. A total of 44 droplets were burned successfully on the two flights, 8 on the shortened STS-83 mission and 36 on STS-94. The results spanned the full range of heptane droplet combustion behavior, from radiative flame extinction at larger droplet diameters in the more dilute atmospheres to diffusive extinction in the less dilute atmospheres, with the droplet disappearing prior to flame extinction at the highest oxygen concentrations. Quasisteady histories of droplet diameters were observed along with unsteady histories of flame diameters. New and detailed information was obtained on burning rates, flame characteristics and soot behavior. The results have motivated new computational and theoretical investigations of droplet combustion, improving knowledge of the chemical kinetics, fluid mechanics and heat and mass transfer processes involved in burning liquid fuels.

Haggard, John B., Jr.↗

NASA NTRS1998

Fiber Supported Droplet Combustion-2 (FSDC-2)

Experimental results for the burning characteristics of fiber supported, liquid droplets in ambient Shuttle cabin air (21% oxygen, 1 bar pressure) were obtained from the Glove Box Facility aboard the STS-94/MSL-1 mission using the Fiber Supported Droplet Combustion - 2 (FSDC-2) apparatus. The combustion of individual droplets of methanol/water mixtures, ethanol, ethanol/water azeotrope, n-heptane, n-decane, and n-heptane/n-hexadecane mixtures were studied in quiescent air. The effects of low velocity, laminar gas phase forced convection on the combustion of individual droplets of n-heptane and n-decane were investigated and interactions of two droplet-arrays of n-heptane and n-decane droplets were also studied with and without gas phase convective flow. Initial diameters ranging from about 2mm to over 6mm were burned on 80-100 micron silicon fibers. In addition to phenomenological observations, quantitative data were obtained in the form of backlit images of the burning droplets, overall flame images, and radiometric combustion emission measurements as a function of the burning time in each experiment. In all, 124 of the 129 attempted experiments (or about twice the number of experiments originally planned for the STS-94/MSL-1 mission) were conducted successfully. The experimental results contribute new observations on the combustion properties of pure alkanes, binary alkane mixtures, and simple alcohols for droplet sizes not studied previously, including measurements on individual droplets and two-droplet arrays, inclusive of the effects of forced gas phase convection. New phenomena characterized experimentally for the first time include radiative extinction of droplet burning for alkanes and the "twin effect" which occurs as a result of interactions during the combustion of two-droplet arrays. Numerical modeling of isolated droplet combustion phenomenon has been conducted for methanol/water mixtures, n-heptane, and n-heptane/n-hexadecane mixtures, and results compare quantitatively with those found experimentally for methanol/water mixtures. Initial computational results qualitatively predict experimental results obtained for isolated n-heptane and n-heptane/n-hexadecane droplet combustion, although the effects of sooting are not yet included in the modeling work. Numerical modeling of ethanol and ethanol/water droplet burning is under development. Considerable data remain to be fully analyzed and will provide a large database for comparisons with further numerical and analytical modeling and development of future free droplet experiments aboard space platforms.

Colantonio, Renato↗

NASA NTRS1998

Fiber-Supported Droplet Combustion

Individual droplets with diameters ranging from about 2 mm to 5 mm were burned under microgravity conditions in air at 1 bar with an ambient temperature of 300 K. Each droplet was tethered by a silicon carbide fiber of 80 mm or 150 mm diameter to keep it in view of video recording, and, in some tests, a forced air flow was applied in a direction parallel to the fiber axis. Methanol, two methanol-water mixtures, two methanol-dodecanol mixtures, and two heptane-hexadecane mixtures were the fuels. Droplet diameters were measured as functions of time and compared with existing theoretical predictions. The prediction that methanol droplets extinguish at diameters that increase with increasing initial droplet diameter is verified by these experiments. In addition, the quasi-steady burning rate constant of the heptane-hexadecane mixtures appears to decrease with increasing droplet diameter; obscuration consistent with very heavy sooting, but without the formation of soot shells, is observed for the largest of these droplets. Forced convective flow around methanol droplets was found to increase the burning rate and to produce a ratio of downstream-to-upstream flame radius that remained constant as the droplet size decreased, a trend in agreement with earlier results obtained at higher convective velocities for smaller droplets having larger flame standoff ratios. There are a number of implications of the experimental results regarding droplet-combustion theory.

Dietrich, Daniel L.↗

NASA NTRS1997

Science Support for Space-Based Droplet Combustion: Drop Tower Experiments and Detailed Numerical Modeling

This program supports the engineering design, data analysis, and data interpretation requirements for the study of initially single component, spherically symmetric, isolated droplet combustion studies. Experimental emphasis is on the study of simple alcohols (methanol, ethanol) and alkanes (n-heptane, n-decane) as fuels with time dependent measurements of drop size, flame-stand-off, liquid-phase composition, and finally, extinction. Experiments have included bench-scale studies at Princeton, studies in the 2.2 and 5.18 drop towers at NASA-LeRC, and both the Fiber Supported Droplet Combustion (FSDC-1, FSDC-2) and the free Droplet Combustion Experiment (DCE) studies aboard the shuttle. Test matrix and data interpretation are performed through spherically-symmetric, time-dependent numerical computations which embody detailed sub-models for physical and chemical processes. The computed burning rate, flame stand-off, and extinction diameter are compared with the respective measurements for each individual experiment. In particular, the data from FSDC-1 and subsequent space-based experiments provide the opportunity to compare all three types of data simultaneously with the computed parameters. Recent numerical efforts are extending the computational tools to consider time dependent, axisymmetric 2-dimensional reactive flow situations.

Marchese, Anthony J.↗

NASA NTRS1993

Computational/experimental studies of isolated, single component droplet combustion

Isolated droplet combustion processes have been the subject of extensive experimental and theoretical investigations for nearly 40 years. The gross features of droplet burning are qualitatively embodied by simple theories and are relatively well understood. However, there remain significant aspects of droplet burning, particularly its dynamics, for which additional basic knowledge is needed for thorough interpretations and quantitative explanations of transient phenomena. Spherically-symmetric droplet combustion, which can only be approximated under conditions of both low Reynolds and Grashof numbers, represents the simplest geometrical configuration in which to study the coupled chemical/transport processes inherent within non-premixed flames. The research summarized here, concerns recent results on isolated, single component, droplet combustion under microgravity conditions, a program pursued jointly with F.A. Williams of the University of California, San Diego. The overall program involves developing and applying experimental methods to study the burning of isolated, single component droplets, in various atmospheres, primarily at atmospheric pressure and below, in both drop towers and aboard space-based platforms such as the Space Shuttle or Space Station. Both computational methods and asymptotic methods, the latter pursued mainly at UCSD, are used in developing the experimental test matrix, in analyzing results, and for extending theoretical understanding. Methanol, and the normal alkanes, n-heptane, and n-decane, have been selected as test fuels to study time-dependent droplet burning phenomena. The following sections summarizes the Princeton efforts on this program, describe work in progress, and briefly delineate future research directions.

Dryer, Frederick L.↗

NASA NTRS1992

Microgravity combustion of isolated n-decane and n-heptane droplets

This paper presents recent experimental results on n-heptane droplet combustion from a 5.0 second Zero-Gravity Facility. For these experiments, droplet sizes from 1 mm to 1.75 mm were studied, oxygen mole fractions in nitrogen ranged from 12 to 21 percent, and the pressure was varied from 0.25 to 1 atm. Disruptive burning mechanisms were observed in some of the experiments conducted in air environments. However, this behavior was inhibited by reducing the oxygen concentration and/or the system pressure. The above results suggest that combinations of lower oxygen indices and reduced ambient pressures are important to reducing the effects of sooting on droplet vaporization-rates.

Choi, Mun Y.↗

NASA NTRS1992

Computational/experimental basis for conducting alkane droplet combustion experiments on space-based-platforms

An analysis is conducted of the requirement for the conduct of spherically symmetric droplet-combustion experiments on space platforms, on the basis of a novel time-dependent computational droplet combustion model that allows the time- and temperature-dependent transport characteristics to be incorporated. While at low oxygen indices the droplet burning extinction becomes a strong function of oxygen index, it becomes a weaker function at higher oxygen index values. The oxygen index that separates these two ranges are dependent on the diluent, being higher for He and lower for N.

Choi, Mun Y.↗

NASA NTRS1991

N-Decane Droplet Combustion in the NASA-Lewis 5 Second Zero-Gravity Facility - Results in Test Gas Environments Other than Air

The burning rate of single droplets of n-decane in a microgravity environment of the NASA-Lewis 5 Second Zero-Gravity Facility was investigated as a function of time, together with the flame diameter/droplet diameter ratio, for a wide range of test environments other than normal air conditions, using an engineering model of the flight experiment. Oxygen mole fractions were varied from 18 to 50 percent, the total test chamber pressure was varied from 0.5 to 2 atmospheres, and the initial droplet diameter was varied from 0.98 to 2.41 mm. Measurements showed that the average burning rates for n-decane droplets exhibited the same qualitative trends as are found in two current models. Temporal analysis of the local burning rates showed variable rates of change in local burning as the droplet combustion progressed. The causes and implications of these findings are discussed.

Haggard, John B.↗

NASA NTRS1991

Some further observations on droplet combustion characteristics - NASA LeRC-Princeton results

Experimental and numerical studies are reviewed which are designed to examine the effects of droplet/gas motion, product-intermediate absorption, extinction, and sooting on droplet combustion. The experimental work at the NASA-Lewis Research Center involves a 2.2-s droptower for investigating microgravitational effects of droplet combustion over a relatively extended range. The droplet-gas velocities are very low because the spherosymmetrical nature of the major combustion processes produces a quiescent environment. The refined experimental results are combined with numerical modeling based on a technique that is fully transient, comprehensive, and has few empirical simplifications. The combination of techniques improves the present understanding of convection-induced effects, reducing soot formation, and promoting quiescent droplet combustion.

Choi, Mun Y.↗

NASA NTRS1991

Observations on a Slow Burning Regime for Hydrocarbon Droplets - N-Heptane/Air Results

Experiments on n-heptane/airdroplet combustion under reduced gravity have served as a benchmark for much of the existing theoretical efforts on the modeling of sphero-synmmetric droplet burning. New experiments conducted in the NASA-Lewis Research Center 2.2 second droptower (at less than 10 exp -5 g) which emphasize the production of sphero-symmetry and low relative droplet/gas convection produce burning rates in air (for about 1 mm droplets) as much as 40-percent lower than the classical result (0.78 sq mm/s). The burning rate is proportional to the measured droplet/gas relative velocity, and the observed functional dependence is much larger than predicted by published convective correlations. New results clearly indicate that the droplet/laboratory velocity does not correspond to the relative droplet/gas velocity. Thus, the convective effects on droplet combustion is not properly characterized by droplet motion alone. Differences in the burning rates are speculated to result from the effects of the accumulated soot as well as the asymmetry (caused by convection) in the temperature and species distributions surrounding the droplet.

Choi, Mun Y.↗