The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Marshall B Long - One of the best experts on this subject based on the ideXlab platform.
-
reaction rate mixture fraction and temperature imaging in turbulent methane air jet flames
Proceedings of the Combustion Institute, 2002Co-Authors: Jonathan H Frank, Sebastian A Kaiser, Marshall B LongAbstract:Instantaneous two-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane/air jet flames. The forward reaction rate of the reaction CO OH ⇒ CO2 H is measured by simultaneous OH laser-induced fluorescence (LIF) and two-photon CO LIF. The product of the two LIF signals is shown to be proportional to the reaction rate. Temperature and Fuel concentration are measured using polarized and depolarized Rayleigh scattering. A three-scalar technique for determining mixture fraction is investigated using a combination of polarized Rayleigh scattering, Fuel concentration, and CO LIF. Measurements of these three quantities are coupled with previous detailed multiscalar point measurements to obtain the most probable value of the mixture fraction at each point in the imaged plane. This technique offers improvements over two-scalar methods, which suffer from decreased sensitivity around the stoichiometric contour and biases in Fuel-rich regions due to Parent Fuel loss. Simultaneous reaction-rate, mixture-fraction, and temperature imaging is demonstrated in laminar (Re 1100) and turbulent (Re 22,400) CH4/air (1/3 by volume) jet flames. The turbulent jet flame is the subject of multiple numerical modeling efforts. A primary objective for developing these imaging diagnostics is to provide measurements of fundamental quantities that are needed to accurately model interactions between turbulent flows and flames.
-
REACTION-RATE, MIXTURE-FRACTION, AND TEMPERATURE IMAGING IN TURBULENT METHANE/AIR JET FLAMES
Proceedings of the Combustion Institute, 2002Co-Authors: Jonathan H Frank, Sebastian A Kaiser, Marshall B LongAbstract:Instantaneous two-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane/air jet flames. The forward reaction rate of the reaction CO OH ⇒ CO2 H is measured by simultaneous OH laser-induced fluorescence (LIF) and two-photon CO LIF. The product of the two LIF signals is shown to be proportional to the reaction rate. Temperature and Fuel concentration are measured using polarized and depolarized Rayleigh scattering. A three-scalar technique for determining mixture fraction is investigated using a combination of polarized Rayleigh scattering, Fuel concentration, and CO LIF. Measurements of these three quantities are coupled with previous detailed multiscalar point measurements to obtain the most probable value of the mixture fraction at each point in the imaged plane. This technique offers improvements over two-scalar methods, which suffer from decreased sensitivity around the stoichiometric contour and biases in Fuel-rich regions due to Parent Fuel loss. Simultaneous reaction-rate, mixture-fraction, and temperature imaging is demonstrated in laminar (Re 1100) and turbulent (Re 22,400) CH4/air (1/3 by volume) jet flames. The turbulent jet flame is the subject of multiple numerical modeling efforts. A primary objective for developing these imaging diagnostics is to provide measurements of fundamental quantities that are needed to accurately model interactions between turbulent flows and flames.
Robert H. Hurt - One of the best experts on this subject based on the ideXlab platform.
-
STRATEGIES AND TECHNOLOGY FOR MANAGING HIGH-CARBON ASH
2004Co-Authors: Robert H. Hurt, Xu Chen, Eric M. Suuberg, John M. Veranth, Indrek KülaotsAbstract:The overall objective of the present project was to identify and assess strategies and solutions for the management of industry problems related to carbon in ash. Specific issues addressed included: (1) the effect of Parent Fuel selection on ash properties and adsorptivity, including a first ever examination of the air entrainment behavior of ashes from alternative (non-coal) Fuels; (2) the effect of various low-NOx firing modes on ash properties and adsorptivity based on pilot-plant studies; and (3) the kinetics and mechanism of ash ozonation. This laboratory data has provided scientific and engineering support and underpinning for parallel process development activities. The development work on the ash ozonation process has now transitioned into a scale-up and commercialization project involving a multi-industry team and scheduled to begin in 2004. This report describes and documents the laboratory and pilot-scale work in the above three areas done at Brown University and the University of Utah during this three-year project.
-
STRATEGIES AND TECHNOLOGY FOR MANAGING HIGH-CARBON ASH
2003Co-Authors: Robert H. Hurt, Eric M. Suuberg, John M. Veranth, Xu ChenAbstract:The overall objective of the present project is to identify and assess strategies and solutions for the management of industry problems related to carbon in ash. Specific research issues to be addressed include: (1) the effect of Parent Fuel selection on ash properties and adsorptivity, including a first ever examination of the air entrainment behavior of ashes from alternative (non-coal) Fuels; (2) the effect of various low-NOx firing modes on ash properties and adsorptivity; and (3) the kinetics and mechanism of ash ozonation. This data will provide scientific and engineering support of the ongoing process development activities. During this fourth project period we completed the characterization of ozone-treated carbon surfaces and wrote a comprehensive report on the mechanism through which ozone suppresses the adsorption of concrete surfactants.
-
The effect of solid Fuel type and combustion conditions on residual carbon properties and fly ash quality
Proceedings of the Combustion Institute, 2002Co-Authors: Yuming Gao, Robert H. Hurt, Indrek Külaots, Xu Chen, Eric M. Suuberg, John M. VeranthAbstract:Research on pulverized Fuel burnout mechanisms derives its primary motivation from industrial problems with the utilization of high-carbon fly ash. The severity of these problems depends on residual carbon properties , but combustion research has focused almost exclusively on the degree of burnout, which determines only the amount of residual carbon. This paper presents measurements of three important residual carbon properties: reactivity, surface area, and adsorptivity toward surfactants, the latter property being the most critical for ash quality in many concrete applications. The paper investigates the independent effects of Fuel type and combustion conditions by analyzing samples derived from bench, pilot, and commercial scale combustion processes. Residual carbon surface area is observed to be strongly dependent on Parent Fuel type ranging from about 1 m 2 /g for petroleum coke residues to values up to 400 m 2 /g for low-rank coal residues. Surfactant adsorptivity also varies strongly with Parent Fuel and shows the best correlation with residual carbon surface area in pores larger than 2 nm, likely because of the large size of surfactant molecules and slow liquid-phase diffusion. The surfactant adsorptivity is also sensitive to the presence of carbon surface oxides introduced by low-temperature oxidation using air or ozone. The data clearly indicate that oxides suppress adsorptivity, and that the underlying mechanism is an increase in carbon surface polarity and hydrophilicity. Controlled pilot-scale experiments show that air staging for NO x control often produces residual carbon with a high adsorptivity, even when adsorptivity is expressed per gram of carbon. Successful staging conditions that lead both to low-NO x and high burnout are observed to produce residual carbons with lower specific surface area and adsorptivity, so poor carbon quality is not an intrinsic feature of all low-NO x flames.
-
Structure, properties, and reactivity of solid Fuels
Symposium (International) on Combustion, 1998Co-Authors: Robert H. HurtAbstract:Solid-Fuel combustion is one of man's oldest technologies, but it continues to play an important societal role as we approach the third millennium. Various economic and environmental factors are leading to a diversification in Fuels—the practitioner can no longer restrict his interest to the combustion behavior of one or several regional coals but must consider a wide variety of potential solid Fuels, including biomass, solid wastes, and internationally traded coals. This paper begins with a brief discussion of the technological issues that define research needs in solid-Fuel combustion and then presents a brief overview of the Fuels themselves and their important fundamental properties. A central theme in the paper is the remarkable variation in the structure, reactivity, and properties of chars from the diverse array of practical solid Fuels. The density, oxidation reactivity, and physical adsorption capacity are identified as key char properties, as they strongly influence the degree of carbon burnout in pulverized Fuel combustion, the volume of the solid waste produced, and the behavior of the resulting fly ash in post-combustion utilization schemes, most notably concrete. Many char properties are shown to depend on char crystalline structure, or nanostructure, which varies from disordered to ordered as a function of precursor chemistry and char formation conditions. Another theme in the paper is the possibility of predicting combustion rates and burnout times of different solid Fuels in a common combustion environment. The paper discusses predictive schemes, which are based on hybrid correlative and mechanistic approaches, in which intraparticle and boundary-layer transport processes are described mechanistically, while surface reactivity and particle density are obtained from empirical correlations with Parent Fuel properties. Although these complex solids are intrinsically more difficult to describe and model than are gaseous and liquid Fuels, there is great potential for developing more fundamental descriptions of the char formation and reaction processes.
-
Reactivity distributions and extinction phenomena in coal char combustion
Energy & Fuels, 1993Co-Authors: Robert H. HurtAbstract:Based on in situ optical measurements and off-line analyses for four coals, the basic features of single-particle pulverized coal char combustion have been elucidated as a function of carbon conversion. Two regimes can be clearly defined: one at low carbon conversion, where the reacting particle populations have properties that are nearly time invariant and a second regime at higher carbon conversion where the distribution properties change dramatically. At low carbon conversion, there is a broad distribution of single-particle combustion rates, reflecting the heterogeneity in the Parent Fuel. Particle-to-particle reactivity differences are shown to be the primary cause of the broad temperature distribution for Pocahontas coal char
Jonathan H Frank - One of the best experts on this subject based on the ideXlab platform.
-
reaction rate mixture fraction and temperature imaging in turbulent methane air jet flames
Proceedings of the Combustion Institute, 2002Co-Authors: Jonathan H Frank, Sebastian A Kaiser, Marshall B LongAbstract:Instantaneous two-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane/air jet flames. The forward reaction rate of the reaction CO OH ⇒ CO2 H is measured by simultaneous OH laser-induced fluorescence (LIF) and two-photon CO LIF. The product of the two LIF signals is shown to be proportional to the reaction rate. Temperature and Fuel concentration are measured using polarized and depolarized Rayleigh scattering. A three-scalar technique for determining mixture fraction is investigated using a combination of polarized Rayleigh scattering, Fuel concentration, and CO LIF. Measurements of these three quantities are coupled with previous detailed multiscalar point measurements to obtain the most probable value of the mixture fraction at each point in the imaged plane. This technique offers improvements over two-scalar methods, which suffer from decreased sensitivity around the stoichiometric contour and biases in Fuel-rich regions due to Parent Fuel loss. Simultaneous reaction-rate, mixture-fraction, and temperature imaging is demonstrated in laminar (Re 1100) and turbulent (Re 22,400) CH4/air (1/3 by volume) jet flames. The turbulent jet flame is the subject of multiple numerical modeling efforts. A primary objective for developing these imaging diagnostics is to provide measurements of fundamental quantities that are needed to accurately model interactions between turbulent flows and flames.
-
REACTION-RATE, MIXTURE-FRACTION, AND TEMPERATURE IMAGING IN TURBULENT METHANE/AIR JET FLAMES
Proceedings of the Combustion Institute, 2002Co-Authors: Jonathan H Frank, Sebastian A Kaiser, Marshall B LongAbstract:Instantaneous two-dimensional measurements of reaction rate, mixture fraction, and temperature are demonstrated in turbulent partially premixed methane/air jet flames. The forward reaction rate of the reaction CO OH ⇒ CO2 H is measured by simultaneous OH laser-induced fluorescence (LIF) and two-photon CO LIF. The product of the two LIF signals is shown to be proportional to the reaction rate. Temperature and Fuel concentration are measured using polarized and depolarized Rayleigh scattering. A three-scalar technique for determining mixture fraction is investigated using a combination of polarized Rayleigh scattering, Fuel concentration, and CO LIF. Measurements of these three quantities are coupled with previous detailed multiscalar point measurements to obtain the most probable value of the mixture fraction at each point in the imaged plane. This technique offers improvements over two-scalar methods, which suffer from decreased sensitivity around the stoichiometric contour and biases in Fuel-rich regions due to Parent Fuel loss. Simultaneous reaction-rate, mixture-fraction, and temperature imaging is demonstrated in laminar (Re 1100) and turbulent (Re 22,400) CH4/air (1/3 by volume) jet flames. The turbulent jet flame is the subject of multiple numerical modeling efforts. A primary objective for developing these imaging diagnostics is to provide measurements of fundamental quantities that are needed to accurately model interactions between turbulent flows and flames.
Massimo Urciuolo - One of the best experts on this subject based on the ideXlab platform.
-
fluidized bed combustion of pelletized biomass and waste derived Fuels
Combustion and Flame, 2008Co-Authors: Riccardo Chirone, Roberto Solimene, Piero Salatino, Fabrizio Scala, Massimo UrciuoloAbstract:The fluidized bed combustion of three pelletized biogenic Fuels (sewage sludge, wood, and straw) has been investigated with a combination of experimental techniques. The Fuels have been characterized from the standpoints of patterns and rates of Fuel devolatilization and char burnout, extent of attrition and fragmentation, and their relevance to the Fuel particle size distribution and the amount and size distribution of primary ash particles. Results highlight differences and similarities among the three Fuels tested. The Fuels were all characterized by limited primary fragmentation and relatively long devolatilization times, as compared with the time scale of particle dispersion away from the Fuel feeding ports in practical FBC. Both features are favorable to effective lateral distribution of volatile matter across the combustor cross section. The three Fuels exhibited distinctively different char conversion patterns. The high-ash pelletized sludge burned according to the shrinking core conversion pattern with negligible occurrence of secondary fragmentation. The low-ash pelletized wood burned according to the shrinking particle conversion pattern with extensive occurrence of secondary fragmentation. The medium-ash pelletized straw yielded char particles with a hollow structure, resembling big cenospheres, characterized by a coherent inorganic outer layer strong enough to prevent particle fragmentation. Inert bed particles were permanently attached to the hollow pellets as they were incorporated into ash melts. Carbon elutriation rates were very small for all the Fuels tested. For pelletized sludge and straw, this was mostly due to the shielding effect of the coherent ash skeleton. For the wood pellet, carbon attrition was extensive, but was largely counterbalanced by effective afterburning due to the large intrinsic reactivity of attrited char fines. The impact of carbon attrition on combustion efficiency was negligible for all the Fuels tested. The size distribution of primary ash particles liberated upon complete carbon burnoff largely reflected the combustion pattern of each Fuel. Primary ash particles of size nearly equal to that of the Parent Fuel were generated upon complete burnoff of the pelletized sludge. Nonetheless, secondary attrition of primary ash from pelletized sludge is large, to the point where generation of fine ash would be extensive over the typical residence time of bed ash in fluidized bed combustors. Very few and relatively fine primary ash particles were released after complete burnoff of wood pellets. Primary ash particles remaining after complete burnoff of pelletized straw had sizes and shapes that were largely controlled by the occurrence of ash agglomeration phenomena.
-
Fluidized bed combustion of pelletized biomass and waste-derived Fuels
Combustion and Flame, 2008Co-Authors: Riccardo Chirone, Roberto Solimene, Piero Salatino, Fabrizio Scala, Massimo UrciuoloAbstract:The fluidized bed combustion of three pelletized biogenic Fuels (sewage Sludge, wood, and straw) has been investigated with a combination of experimental techniques. The Fuels have been characterized from the standpoints of patterns and rates of Fuel devolatilization and char burnout, extent of attrition and fragmentation, and their relevance to the Fuel particle size distribution and the amount and size distribution of primary ash particles. Results highlight differences and similarities among the three Fuels tested. The Fuels were all characterized by limited primary fragmentation and relatively long devolatilization times, as compared with the time scale of particle dispersion away from the Fuel feeding ports in practical FBC. Both features are favorable to effective lateral distribution of volatile matter across the combustor cross section. The three Fuels exhibited distinctively different char conversion patterns. The high-ash pelletized sludge burned according to the shrinking core conversion pattern with negligible Occurrence of secondary fragmentation. The low-ash pelletized wood burned according to the shrinking particle conversion pattern with extensive occurrence of secondary fragmentation. The medium-ash pelletized straw yielded char particles with a hollow structure, resembling big cenospheres, characterized by a coherent inorganic outer layer strong enough to prevent particle fragmentation. Inert bed particles were permanently attached to the hollow pellets as they were incorporated into ash melts. Carbon elutriation rates were very small for all the Fuels tested. For pelletized sludge and straw, this was mostly due to the shielding effect of the coherent ash skeleton. For the wood pellet, carbon attrition was extensive, but was largely counterbalanced by effective afterburning due to the large intrinsic reactivity of attrited char fines. The impact of carbon attrition on combustion efficiency was negligible for all the Fuels tested. The size distribution of primary ash particles liberated upon complete carbon burnoff largely reflected the combustion pattern of each Fuel. Primary ash particles of size nearly equal to that of the Parent Fuel were generated upon complete burnoff of the pelletized sludge. Nonetheless, secondary attrition of primary ash from pelletized sludge is large, to the point where generation of fine ash would be extensive over the typical residence time of bed ash in fluidized bed combustors. Very few and relatively fine primary ash particles were released after complete burnoff of wood pellets. Primary ash particles remaining after complete burnoff of pelletized straw had sizes and shapes that were largely controlled by the Occurrence of ash agglomeration phenomena. (c) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved
-
Attrition phenomena during fluidized bed combustion of granulated and mechanically dewatered sewage sludges
Proceedings of the Combustion Institute, 2005Co-Authors: A. Cammarota, Riccardo Chirone, Piero Salatino, Fabrizio Scala, Massimo UrciuoloAbstract:Abstract Fluidized bed combustion of two types of sewage sludge was investigated in a bench scale reactor. The sludges differed as regards their preparation: one sludge was mechanically dewatered, the other was dried and granulated. The single particle conversion pattern and rate, and the nature and extent of attrition phenomena occurring during burn-off were quantitatively assessed. Primary fragmentation and conversion patterns of the residual char were characterized by periodic retrieval of Fuel particles from the bed using a basket. Attrition by abrasion was assessed by collection of elutriated fines at the exhaust during batch fluidized bed combustion of chars of the two sludges. The size distribution of primary ash particles (PAPSD), relevant to bed inventory, particle size distribution, and balance between fly- and bottom-ash during steady fluidized bed combustion, was characterized using a purposely designed experimental procedure. Primary fragmentation was negligible for the granulated sludge, moderate for the mechanically dewatered one. Both sludges are characterized by the formation of coherent ash skeletons, responsible for a shrinking unreacted core conversion pattern of the char particles. Carbon attrition was very limited, as the coherent ash skeleton acted as a mechanical shield with respect to the unreacted carbon-rich core. The PAPSD closely followed the size distribution of the Parent Fuel particles for the granulated sludge, while it was slightly shifted to smaller sizes for the mechanically dewatered one. A simple combustion model, based on the shrinking core conversion model, has been developed to analyse the combustion behaviour of sludge char particles. The model is based on the consideration of resistances to mass transfer both in the boundary layer around the particle and in the carbon-depleted ash shell. The model satisfactorily reproduces the main features of the fluidized bed combustion of both sludges under the experimental conditions tested.
Alessandro Gomez - One of the best experts on this subject based on the ideXlab platform.
-
Small aromatic hydrocarbons control the onset of soot nucleation
Combustion and Flame, 2021Co-Authors: Kevin Gleason, Francesco Carbone, Andrew J. Sumner, Brian D. Drollette, Desiree L. Plata, Alessandro GomezAbstract:Abstract The gas-to-particle transition is a critical and hitherto poorly understood aspect in carbonaceous soot particle formation. Polycyclic Aromatic Hydrocarbons (PAHs) are key precursors of the solid phase, but their role has not been assessed quantitatively probably because, even if analytical techniques to quantify them are well developed, the challenge to adapt them to flame environments are longstanding. Here, we present simultaneous measurements of forty-eight gaseous species through gas capillary-sampling followed by chemical analysis and of particle properties by optical techniques. Taken together, they enabled us to follow quantitatively the transition from Parent Fuel molecule to PAHs and, eventually, soot. Importantly, the approach resolved spatially the structure of flames even in the presence of steep gradients and, in turn, allowed us to follow the molecular growth process in unprecedented detail. Noteworthy is the adaptation to a flame environment of a novel technique based on trapping semi-volatile compounds in a filter, followed by off-line extraction and preconcentration for quantitative chemical analyses of species at mole fractions as low as parts per billion. The technique allowed for the quantitation of PAHs containing up to 6 aromatic rings. The principal finding is that only one- and two-ring aromatic compounds can account for soot nucleation, and thus provide the rate-limiting step in the reactions leading to soot. This finding impacts the fundamental understanding of soot formation and eases the modeling of soot nucleation by narrowing the precursors that must be predicted accurately.
-
PAHs controlling soot nucleation in 0.101—0.811MPa ethylene counterflow diffusion flames
Combustion and Flame, 2021Co-Authors: Kevin Gleason, Francesco Carbone, Alessandro GomezAbstract:Abstract On the heels of a recent study in an atmospheric pressure ethylene diffusion flame in which the transition from Parent Fuel molecule to Polycyclic Aromatic Hydrocarbons (PAHs) and, eventually, soot was studied by spatially resolved measurements of PAH concentrations and soot quantities, we extended the focus to diffusion flames with self- similar structure in the 0.101–0.811 MPa pressure range. To that end, we complemented pyrometry based measurements of soot volume fraction with light scattering measurements that, once corrected for beam steering, yielded soot particle size and number concentration profiles. A chemistry model, that had been validated for all species up to 3 ring aromatics in one of the flames investigated at each pressure and up to 4-rings for the flame at atmospheric pressure, was used to compare profiles of chemical species to those of soot quantities. Further analysis yielded the assessment of number nucleation rates of soot and their comparison to the dimerization rates of PAHs. Soot nucleation rate is consistent only with the dimerization of one- and two-ring PAHs, an observation that confirms findings in the atmospheric pressure flame. Changes in pressure and temperature have a progressively larger impact on the concentration of aromatics of increasingly larger molecular weight and, even more so, on soot volume fraction and nucleation rate. A four-fold increase in pressure from 0.101 MPa to 0.405 MPa increases the soot nucleation rate and PAH dimerization rate in flames with constant peak temperature, which is primarily a concentration effect on bimolecular collision rates; a similar but less pronounced effect is observed in the higher (0.405–0.811 MPa) pressure range. Changes in pressure and temperature tend to be progressively more consequential on aromatics of increasing molecular weight and soot.
-
Experimental and computational study of methane counterflow diffusion flames perturbed by trace amounts of either jet Fuel or a 6-component surrogate under non-sooting conditions
Combustion and Flame, 2009Co-Authors: Hugo Bufferand, Luca Tosatto, B. La Mantia, Mitchell D. Smooke, Alessandro GomezAbstract:The chemical structure of a methane counterflow diffusion flame and of the same flame doped with 1000 ppm (molar) of either jet Fuel or a 6-component jet Fuel surrogate was analyzed experimentally, by gas sampling via quartz microprobes and subsequent GC/MS analysis, and computationally using a semi-detailed kinetic mechanism for the surrogate blend. Conditions were chosen to ensure that all three flames were non-sooting, with identical temperature profiles and stoichiometric mixture fraction, through a judicious selection of feed stream composition and strain rate. The experimental dataset provides a glimpse of the pyrolysis and oxidation behavior of jet Fuel in a diffusion flame. The jet Fuel initial oxidation is consistent with anticipated chemical kinetic behavior, based on thermal decomposition of large alkanes to smaller and smaller fragments and the survival of ring-stabilized aromatics at higher temperatures. The 6-component surrogate captures the same trend correctly, but the agreement is not quantitative with respect to some of the aromatics such as benzene and toluene. Various alkanes, alkenes and aromatics among the jet Fuel components are either only qualitatively characterized or could not be identified, because of the presence of many isomers and overlapping spectra in the chromatogram, leaving 80% of the carbon from the jet Fuel unaccounted for in the early pyrolysis history of the Parent Fuel. Computationally, the one-dimensional code adopted a semi-detailed kinetic mechanism for the surrogate blend that is based on an existing hierarchically constructed kinetic model for alkanes and simple aromatics, extended to account for the presence of tetralin and methylcyclohexane as reference Fuels. The computational results are in reasonably good agreement with the experimental ones for the surrogate behavior, with the greatest discrepancy in the concentrations of aromatics and ethylene.
