The Experts below are selected from a list of 177 Experts worldwide ranked by ideXlab platform
A A Mantashyan - One of the best experts on this subject based on the ideXlab platform.
-
Peculiarities of the Slow Combustion of a hydrocarbon in a “wall-less” reactor ith laser heating
Combustion and Flame, 1998Co-Authors: A A MantashyanAbstract:The Slow Combustion of the simplest hydrocarbons in a wall-less reactor with laser heating has been studied. In such a reactor, Combustion proceeds in the laser beam, while the reactor`s wall is at room temperature and does not take part in the process. It has been shown that conversion of propane plus oxygen mixtures can be observed at temperatures above 800 K. Ethylene, propylene, methane, and hydrogen were found to be the major products, indicating the dominant role of the cracking route in this process. At the same time oxygen was not consumed and oxygenated products were detected only in trace concentrations. However, in the absence of oxygen the cracking process does not proceed. Chain initiation in a wall-less reactor occurs homogeneously, while, in conventional heated reactors chain initiation is provided at lower temperatures (600--650 K) by heterogeneous reactions on the reactor`s wall. It has been established that the reversible reaction forming alkyl peroxy radicals in R + O{sub 2} = RO{sub 2} is of great importance in the competition between oxidative and cracking routes. In a wall-less reactor when a sufficient rate of chain initiation can be reached at temperatures above 800 K, this equilibrium is shifted to formmore » alkyl radicals. Reactions of these radicals become dominant and hydrocarbon conversion leads to products from cracking. The conversion of methane plus oxygen mixtures starts at temperatures {approx} 1,000 K and proceeds via the oxidative route, because methyl radicals, unlike propyl radicals, do not decay, but react with oxygen in different ways. The results reveal the role of heterogeneous factors in the chemistry of Slow Combustion and show ways to carry out these processes with a high selectivity.« less
-
peculiarities of the Slow Combustion of a hydrocarbon in a wall less reactor ith laser heating
Combustion and Flame, 1998Co-Authors: A A MantashyanAbstract:The Slow Combustion of the simplest hydrocarbons in a wall-less reactor with laser heating has been studied. In such a reactor, Combustion proceeds in the laser beam, while the reactor`s wall is at room temperature and does not take part in the process. It has been shown that conversion of propane plus oxygen mixtures can be observed at temperatures above 800 K. Ethylene, propylene, methane, and hydrogen were found to be the major products, indicating the dominant role of the cracking route in this process. At the same time oxygen was not consumed and oxygenated products were detected only in trace concentrations. However, in the absence of oxygen the cracking process does not proceed. Chain initiation in a wall-less reactor occurs homogeneously, while, in conventional heated reactors chain initiation is provided at lower temperatures (600--650 K) by heterogeneous reactions on the reactor`s wall. It has been established that the reversible reaction forming alkyl peroxy radicals in R + O{sub 2} = RO{sub 2} is of great importance in the competition between oxidative and cracking routes. In a wall-less reactor when a sufficient rate of chain initiation can be reached at temperatures above 800 K, this equilibrium is shifted to formmore » alkyl radicals. Reactions of these radicals become dominant and hydrocarbon conversion leads to products from cracking. The conversion of methane plus oxygen mixtures starts at temperatures {approx} 1,000 K and proceeds via the oxidative route, because methyl radicals, unlike propyl radicals, do not decay, but react with oxygen in different ways. The results reveal the role of heterogeneous factors in the chemistry of Slow Combustion and show ways to carry out these processes with a high selectivity.« less
Robert Louw - One of the best experts on this subject based on the ideXlab platform.
-
Gas‐Phase Chemistry of Chlorinated Phenols − Formation of Dibenzofurans and Dibenzodioxins in Slow Combustion
European Journal of Organic Chemistry, 2001Co-Authors: Izabela Wiater−protas, Robert LouwAbstract:The effects of the introduction of chlorine substituents onto phenol on the rates of, and products from, their Slow Combustion at 500−550 °C are described. Competitive experiments showed that phenol, ortho-chlorophenol, 2,4,6-trichlorophenol and pentachlorophenol differ little in their overall rates of conversion − mainly into CO/CO2. Provided that an ortho-H moiety is available, chlorinated dibenzofurans (DFs) rather than dibenzodioxins (DDs) are formed as (cross)condensation products. Overall rates of formation, through (reversible) ortho-C, ortho-C combination of two (chloro)phenoxy radicals, are discussed on a thermokinetic basis, using new data relating to the O−H bond strengths in the target phenols. Chlorinated DDs are the predominant condensation products only when the ortho positions are fully chlorinated, a situation insignificant during thermal Combustion of real waste. The question of mechanism is merely of scientific interest, but thermokinetic evaluation together with an experimental check on the behaviour of ′triclosan’ − a model o-hydroxy-diphenyl ether intermediate − provides the conclusion that both radical/radical combination and radical/molecule reaction may be involved in this case, with displacement of o-Cl by a (chloro)phenoxy radical. As chlorinated DFs and unconverted (chloro)phenols in real incinerators are subject to further reaction − (oxy)chlorination of the DFs, and condensation of the phenols to DDs − catalysed by ashes in the pollution control devices, the mixture of polychlorinated DFs and DDs commonly found in incinerator emissions can be viewed as arising from (chloro)phenols as the only important precursors.
-
gas phase chemistry of chlorinated phenols formation of dibenzofurans and dibenzodioxins in Slow Combustion
European Journal of Organic Chemistry, 2001Co-Authors: Izabela Wiater Protas, Robert LouwAbstract:The effects of the introduction of chlorine substituents onto phenol on the rates of, and products from, their Slow Combustion at 500−550 °C are described. Competitive experiments showed that phenol, ortho-chlorophenol, 2,4,6-trichlorophenol and pentachlorophenol differ little in their overall rates of conversion − mainly into CO/CO2. Provided that an ortho-H moiety is available, chlorinated dibenzofurans (DFs) rather than dibenzodioxins (DDs) are formed as (cross)condensation products. Overall rates of formation, through (reversible) ortho-C, ortho-C combination of two (chloro)phenoxy radicals, are discussed on a thermokinetic basis, using new data relating to the O−H bond strengths in the target phenols. Chlorinated DDs are the predominant condensation products only when the ortho positions are fully chlorinated, a situation insignificant during thermal Combustion of real waste. The question of mechanism is merely of scientific interest, but thermokinetic evaluation together with an experimental check on the behaviour of ′triclosan’ − a model o-hydroxy-diphenyl ether intermediate − provides the conclusion that both radical/radical combination and radical/molecule reaction may be involved in this case, with displacement of o-Cl by a (chloro)phenoxy radical. As chlorinated DFs and unconverted (chloro)phenols in real incinerators are subject to further reaction − (oxy)chlorination of the DFs, and condensation of the phenols to DDs − catalysed by ashes in the pollution control devices, the mixture of polychlorinated DFs and DDs commonly found in incinerator emissions can be viewed as arising from (chloro)phenols as the only important precursors.
-
On the possible role of acetylene in gas-phase dioxin formation.
Chemosphere, 2000Co-Authors: Mariusz K. Cieplik, Maria Cairols Oviedo, Robert LouwAbstract:Abstract The Slow Combustion of benzene/phenol gives rise to dibenzofuran (DBF) as major product of incomplete Combustion, with negligible proportions of dibenzo- p -dioxin (DBD), or benzofuran (BF). Contrary to a recent proposal that acetylene growth reactions, e.g. BF → DBF, are important in dioxin formation, co-Combustion of benzene/phenol with acetylene – around 550°C – did not alter this product pattern. Also, BF was identified as a product from degradation of DBF.
-
Thermal and catalysed halogenation in Combustion reactions
Chemosphere, 1999Co-Authors: Jacqueline Kanters, Robert LouwAbstract:Abstract Organic vapors in hot air with HCl can form organic chlorine derivatives, parallel to their oxidative degradation, even without catalysis (fly-ash). Upon Slow Combustion in an inert quartz reactor with incomplete conversion, phenol - a key precursor for PCDDs - indeed gave o-/p-chlorinated phenols, together with a variety of other PICs. With HBr plus HCl at ca. 900K, the (net) production rate of brominated phenol was ca 10 x that of Cl-phenol. These uncatalysed processes can be explained via free-radical mechanisms, with Cl 2 , Cl· and possibly HOCl as chlorine transfer agents. Bromination occurs via free Br atoms. Slow Combustion of phenol plus acetone (at ca. 630°C) also led to methylchloride. In real (waste) Combustion, metal salts catalyse (oxy)chlorination, and presumably oxidation also. In a model experiment, a piece of quartz tubelet ‘aged’ with inorganics emanated from real municipal solid waste was placed in a clean quartz reactor - with a volume 70 x that of the tubelet; at 900K this led to a 10 2 fold increase in the level of o-/p-chlorophenol. Also, chlorobenzenes, PCDDs, PCDFs and C2Cl4 were now noticed, at comparable levels.
-
Slow Combustion of pentachlorophenol in toluene
Chemosphere, 1996Co-Authors: Jacqueline M Kanters, Robert LouwAbstract:Upon ‘lean’ Slow Combustion 0f 2 mol % of PCP in toluene at 700 °C, the outflow contains a > 102 fold excess of Cl-free phenol on remaining PCP. Next to dibenzofuran (DF) — the condensation product of 2 phenoxy radicals - (1,2,3,4-)TCDF is observed, but almost no TODD. The TCDF is explained to arise from a phenoxy and a pentachlorophenoxy radical; reactions between (chloro)phenoxy radicals and (chloro)phenols — as in the ‘Shaub and Tsang’ mechanism — appear to be of minor importance. The significance of these results for the formation in incinerators of lower chlorinated DFs and DDs — which could be precursors t0 PCDD/Fs generated in the cooling zone — is also discussed.
J Timonen - One of the best experts on this subject based on the ideXlab platform.
-
Experimental determination of KPZ height-fluctuation distributions
The European Physical Journal B - Condensed Matter and Complex Systems, 2005Co-Authors: L. Miettinen, J Merikoski, M. Myllys, J TimonenAbstract:Height-fluctuation distributions of nonequilibrium interfaces were analyzed using Slow-Combustion fronts propagating in sheets of paper. All distributions measured were definitely non-Gaussian. The experimental distributions for transient and stationary regimes were well fitted by the theoretical distributions proposed by Prähofer and Spohn in reference [9]. Consistent with the Galilean invariance of the system, the same distributions were found for horizontal fronts and, when determined along the normal to the slope, for fronts with a non-zero average slope.
-
effect of a columnar defect on the shape of Slow Combustion fronts
Physical Review E, 2003Co-Authors: Markko Myllys, J Maunuksela, J Timonen, J Merikoski, Viktor Horvath, Meesoon Ha, Den M NijsAbstract:: We report experimental results for the behavior of Slow-Combustion fronts in the presence of a columnar defect with enhanced or reduced driving, and compare them with those of mean-field theory. We also compare them with simulation results for an analogous problem of driven flow of particles with hard-core repulsion (ASEP) and a single defect bond with a different hopping probability. The difference in the shape of the front profiles for enhanced vs reduced driving in the defect clearly demonstrates the existence of a Kardar-Parisi-Zhang-type nonlinear term in the effective evolution equation for the Slow-Combustion fronts. We also find that Slow-Combustion fronts display a faceted form for large enough enhanced driving, and that there is a corresponding increase then in the average front speed. This increase in the average front speed disappears at a nonzero enhanced driving in agreement with the simulated behavior of the ASEP model.
-
Temporal and spatial persistence of Combustion fronts in paper.
Physical Review Letters, 2003Co-Authors: Juha Merikoski, Markko Myllys, J Maunuksela, J Timonen, Mikko J AlavaAbstract:The spatial and temporal persistence, or first-return distributions are measured for Slow-Combustion fronts in paper. The stationary temporal and (perhaps less convincingly) spatial persistence exponents agree with the predictions based on the front dynamics, which asymptotically belongs to the Kardar-Parisi-Zhang universality class. The stationary short-range and the transient behavior of the fronts are non-Markovian, and the observed persistence properties thus do not agree with the predictions based on Markovian theory. This deviation is a consequence of additional time and length scales, related to the crossovers to the asymptotic coarse-grained behavior.
-
Kinetic roughening in Slow Combustion of paper
Physical Review E, 2001Co-Authors: Markko Myllys, J Maunuksela, Mikko J Alava, J Merikoski, T. Ala-nissila, J TimonenAbstract:Results of experiments on the dynamics and kinetic roughening of one-dimensional Slow-Combustion fronts in three grades of paper are reported. Extensive averaging of the data allows a detailed analysis of the spatial and temporal development of the interface fluctuations. The asymptotic scaling properties, on long length and time scales, are well described by the Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To obtain a more detailed picture of the strong-coupling fixed point, characteristic of the KPZ universality class, universal amplitude ratios, and the universal coupling constant are computed from the data and found to be in good agreement with theory. Below the spatial and temporal scales at which a cross-over takes place to the standard KPZ behavior, the fronts display higher apparent exponents and apparent multiscaling. In this regime the interface velocities are spatially and temporally correlated, and the distribution of the magnitudes of the effective noise has a power-law tail. The relation of the observed short-range behavior and the noise as determined from the local velocity fluctuations is discussed.Comment: RevTeX v3.1, 13 pages, 12 Postscript figures (uses epsf.sty), 3 tables; submitted to Phys. Rev.
-
scaling and noise in Slow Combustion of paper
Physical Review Letters, 2000Co-Authors: Markko Myllys, J Maunuksela, Mikko J Alava, Tapio Alanissila, J TimonenAbstract:: We present results of high resolution experiments on kinetic roughening of Slow Combustion fronts in paper, focusing on short length and time scales. Using three different grades of paper, we find that the Combustion fronts show apparent spatial and temporal multiscaling at short scales. The scaling exponents decrease as a function of the order of the corresponding correlation functions. The noise affecting the fronts reveals short range temporal and spatial correlations, and non-Gaussian noise amplitudes. Our results imply that the overall behavior of Slow Combustion fronts cannot be explained by standard theories of kinetic roughening.
Markko Myllys - One of the best experts on this subject based on the ideXlab platform.
-
effect of a columnar defect on the shape of Slow Combustion fronts
Physical Review E, 2003Co-Authors: Markko Myllys, J Maunuksela, J Timonen, J Merikoski, Viktor Horvath, Meesoon Ha, Den M NijsAbstract:: We report experimental results for the behavior of Slow-Combustion fronts in the presence of a columnar defect with enhanced or reduced driving, and compare them with those of mean-field theory. We also compare them with simulation results for an analogous problem of driven flow of particles with hard-core repulsion (ASEP) and a single defect bond with a different hopping probability. The difference in the shape of the front profiles for enhanced vs reduced driving in the defect clearly demonstrates the existence of a Kardar-Parisi-Zhang-type nonlinear term in the effective evolution equation for the Slow-Combustion fronts. We also find that Slow-Combustion fronts display a faceted form for large enough enhanced driving, and that there is a corresponding increase then in the average front speed. This increase in the average front speed disappears at a nonzero enhanced driving in agreement with the simulated behavior of the ASEP model.
-
Determination of the stochastic evolution equation from noisy experimental data
European Physical Journal B, 2003Co-Authors: J Maunuksela, Markko Myllys, Jussi Timonen, Juha Merikoski, Tommi Kärkkäinen, M. S. Welling, Rinke J. WijngaardenAbstract:We have determined the coefficients of the Kardar-Parisi-Zhang equation as functions of coarse graining, which best describe the time evolution and spatial behavior observed for Slow-Combustion fronts in sheets of paper and magnetic flux fronts in a thin-film high-Tc superconductor. Reconstruction of the relevant equation of motion and its coefficients was mainly based on the inverse method proposed by Lam and Sander [Phys. Rev. Lett. 71, 561 (1993)]. The coefficient of the nonlinear term was also determined from the local slope-dependence of the front velocity.
-
Temporal and spatial persistence of Combustion fronts in paper.
Physical Review Letters, 2003Co-Authors: Juha Merikoski, Markko Myllys, J Maunuksela, J Timonen, Mikko J AlavaAbstract:The spatial and temporal persistence, or first-return distributions are measured for Slow-Combustion fronts in paper. The stationary temporal and (perhaps less convincingly) spatial persistence exponents agree with the predictions based on the front dynamics, which asymptotically belongs to the Kardar-Parisi-Zhang universality class. The stationary short-range and the transient behavior of the fronts are non-Markovian, and the observed persistence properties thus do not agree with the predictions based on Markovian theory. This deviation is a consequence of additional time and length scales, related to the crossovers to the asymptotic coarse-grained behavior.
-
Kinetic roughening in Slow Combustion of paper
Physical Review E, 2001Co-Authors: Markko Myllys, J Maunuksela, Mikko J Alava, J Merikoski, T. Ala-nissila, J TimonenAbstract:Results of experiments on the dynamics and kinetic roughening of one-dimensional Slow-Combustion fronts in three grades of paper are reported. Extensive averaging of the data allows a detailed analysis of the spatial and temporal development of the interface fluctuations. The asymptotic scaling properties, on long length and time scales, are well described by the Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To obtain a more detailed picture of the strong-coupling fixed point, characteristic of the KPZ universality class, universal amplitude ratios, and the universal coupling constant are computed from the data and found to be in good agreement with theory. Below the spatial and temporal scales at which a cross-over takes place to the standard KPZ behavior, the fronts display higher apparent exponents and apparent multiscaling. In this regime the interface velocities are spatially and temporally correlated, and the distribution of the magnitudes of the effective noise has a power-law tail. The relation of the observed short-range behavior and the noise as determined from the local velocity fluctuations is discussed.Comment: RevTeX v3.1, 13 pages, 12 Postscript figures (uses epsf.sty), 3 tables; submitted to Phys. Rev.
-
scaling and noise in Slow Combustion of paper
Physical Review Letters, 2000Co-Authors: Markko Myllys, J Maunuksela, Mikko J Alava, Tapio Alanissila, J TimonenAbstract:: We present results of high resolution experiments on kinetic roughening of Slow Combustion fronts in paper, focusing on short length and time scales. Using three different grades of paper, we find that the Combustion fronts show apparent spatial and temporal multiscaling at short scales. The scaling exponents decrease as a function of the order of the corresponding correlation functions. The noise affecting the fronts reveals short range temporal and spatial correlations, and non-Gaussian noise amplitudes. Our results imply that the overall behavior of Slow Combustion fronts cannot be explained by standard theories of kinetic roughening.
J Maunuksela - One of the best experts on this subject based on the ideXlab platform.
-
effect of a columnar defect on the shape of Slow Combustion fronts
Physical Review E, 2003Co-Authors: Markko Myllys, J Maunuksela, J Timonen, J Merikoski, Viktor Horvath, Meesoon Ha, Den M NijsAbstract:: We report experimental results for the behavior of Slow-Combustion fronts in the presence of a columnar defect with enhanced or reduced driving, and compare them with those of mean-field theory. We also compare them with simulation results for an analogous problem of driven flow of particles with hard-core repulsion (ASEP) and a single defect bond with a different hopping probability. The difference in the shape of the front profiles for enhanced vs reduced driving in the defect clearly demonstrates the existence of a Kardar-Parisi-Zhang-type nonlinear term in the effective evolution equation for the Slow-Combustion fronts. We also find that Slow-Combustion fronts display a faceted form for large enough enhanced driving, and that there is a corresponding increase then in the average front speed. This increase in the average front speed disappears at a nonzero enhanced driving in agreement with the simulated behavior of the ASEP model.
-
Determination of the stochastic evolution equation from noisy experimental data
European Physical Journal B, 2003Co-Authors: J Maunuksela, Markko Myllys, Jussi Timonen, Juha Merikoski, Tommi Kärkkäinen, M. S. Welling, Rinke J. WijngaardenAbstract:We have determined the coefficients of the Kardar-Parisi-Zhang equation as functions of coarse graining, which best describe the time evolution and spatial behavior observed for Slow-Combustion fronts in sheets of paper and magnetic flux fronts in a thin-film high-Tc superconductor. Reconstruction of the relevant equation of motion and its coefficients was mainly based on the inverse method proposed by Lam and Sander [Phys. Rev. Lett. 71, 561 (1993)]. The coefficient of the nonlinear term was also determined from the local slope-dependence of the front velocity.
-
Temporal and spatial persistence of Combustion fronts in paper.
Physical Review Letters, 2003Co-Authors: Juha Merikoski, Markko Myllys, J Maunuksela, J Timonen, Mikko J AlavaAbstract:The spatial and temporal persistence, or first-return distributions are measured for Slow-Combustion fronts in paper. The stationary temporal and (perhaps less convincingly) spatial persistence exponents agree with the predictions based on the front dynamics, which asymptotically belongs to the Kardar-Parisi-Zhang universality class. The stationary short-range and the transient behavior of the fronts are non-Markovian, and the observed persistence properties thus do not agree with the predictions based on Markovian theory. This deviation is a consequence of additional time and length scales, related to the crossovers to the asymptotic coarse-grained behavior.
-
Kinetic roughening in Slow Combustion of paper
Physical Review E, 2001Co-Authors: Markko Myllys, J Maunuksela, Mikko J Alava, J Merikoski, T. Ala-nissila, J TimonenAbstract:Results of experiments on the dynamics and kinetic roughening of one-dimensional Slow-Combustion fronts in three grades of paper are reported. Extensive averaging of the data allows a detailed analysis of the spatial and temporal development of the interface fluctuations. The asymptotic scaling properties, on long length and time scales, are well described by the Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To obtain a more detailed picture of the strong-coupling fixed point, characteristic of the KPZ universality class, universal amplitude ratios, and the universal coupling constant are computed from the data and found to be in good agreement with theory. Below the spatial and temporal scales at which a cross-over takes place to the standard KPZ behavior, the fronts display higher apparent exponents and apparent multiscaling. In this regime the interface velocities are spatially and temporally correlated, and the distribution of the magnitudes of the effective noise has a power-law tail. The relation of the observed short-range behavior and the noise as determined from the local velocity fluctuations is discussed.Comment: RevTeX v3.1, 13 pages, 12 Postscript figures (uses epsf.sty), 3 tables; submitted to Phys. Rev.
-
scaling and noise in Slow Combustion of paper
Physical Review Letters, 2000Co-Authors: Markko Myllys, J Maunuksela, Mikko J Alava, Tapio Alanissila, J TimonenAbstract:: We present results of high resolution experiments on kinetic roughening of Slow Combustion fronts in paper, focusing on short length and time scales. Using three different grades of paper, we find that the Combustion fronts show apparent spatial and temporal multiscaling at short scales. The scaling exponents decrease as a function of the order of the corresponding correlation functions. The noise affecting the fronts reveals short range temporal and spatial correlations, and non-Gaussian noise amplitudes. Our results imply that the overall behavior of Slow Combustion fronts cannot be explained by standard theories of kinetic roughening.