Showing papers in "Combustion Science and Technology in 1992"
TL;DR: In this paper, the authors investigated the displacement speed of a curved flame in a non-uniform flow field, and showed that three different mechanisms affect the displacement of a curve flame in such a flow field: a chemical mechanism associated with the expansion of the reaction zone structure, a hydrodynamic mechanism due to isothermal area modification by lateral flow divergence, and a linear flow divergence.
Abstract: Flame surface curvature is a significant geometrical parameter that affects the structure and propagation of premixed laminar and turbulent flames. In this study, the flame tip of a two-dimensional laminar Bunsen burner is investigated using a quasi-one dimensional model, direct numerical simulations and experimental results. The laminar flame tip is a simple prototype of curved flamelets embedded in a turbulent flow field. It is shown that two characteristic flame speeds are necessary to give a local description of a given flamelet: the consumption speed associated with the structure of the reaction zone, and the displacement speed of the flame front relative to the unburned flow. The quasi-one dimensional model shows that three different mechanisms affect the displacement speed of a curved flame in a non-uniform flow field: a chemical mechanism associated with the expansion of the reaction zone structure, a hydrodynamic mechanism due to isothermal area modification by lateral flow divergence an...
247 citations
TL;DR: In this paper, the authors present an experimental description of the acoustic instability of a premixed flame front propagating in a tube and identify four distinct types of behaviour: cellular, quasi planar, secondary and auto-turbulent.
Abstract: This short paper presents an experimental description of the acoustic instability of a premixed flame front propagating in a tube. Four distinct types of behaviour are identified. Firstly a regime of acoustic stability in which the flame is cellular and non vibrating. Secondly a regime of primary acoustic instability in which the flame is quasi planar. Thirdly a regime of secondary acoustic instability, in which the oscillations can reach very high amplitudes, and where the flame front develops pulsating cellular structures. This latter regime breaks down into an incoherent auto-turbulent regime at sufficiently high acoustic amplitudes.
155 citations
TL;DR: It is shown that adaptive control algorithms may be used to suppress combustion instabilities in turbulent combustors by using a numerical adaptive filter to control the different unstable modes of oscillation.
Abstract: It is shown in this article that adaptive control algorithms may be used to suppress combustion instabilities in turbulent combustors. In a typical configuration a signal delivered by a sensor monitoring the flame serves as input to a numerical adaptive filter which sends a control signal through an actuator into the combustion chamber. The controller coefficients are updated at the sampling rate using a global response signal. The controller automatically finds optimal coefficients to control the different unstable modes of oscillation. In addition it adapts to evolutions in operating conditions such as a continuous sweep of air flow rate and a shift in the global equivalence ratio. Under certain conditions a secondary mode appears when the control system is operating. While this oscillation occurs as a result of a destabilizing effect of the control loop its amplitude remains limited. The theoretical background is developed and used to explain typical implementation problems such as the filter ...
146 citations
TL;DR: In this article, a numerical and experimental study of hydroxyl radical chemiluminescence from methane-air flames was performed, and it was found that the chemilumininescence intensity was highly dependent on the equivalence ratio.
Abstract: A numerical and experimental study of hydroxyl radical chemiluminescence from methane-air flames was performed. Measurements of the chemiluminescence per unit flame area for lean methane-air flames were obtained, and a model for use in predicting chemiluminescence was developed. The model was one-dimensional and unsteady, incorporating the equations of species continuity and energy, with temperature- and concentration-dependent transport and thermodynamic properties. The reaction mechanism included the chemiluminescent reaction, as well as reactions that both produced and quenched electronically excited OH. It was found, both experimentally and numerically, that the chemiluminescent intensity was highly dependent on the equivalence ratio. For !he range of equivalence ratios studied experimentally (0·65 < φ < 0·90) there was an exponential dependence of chemiluminescence on equivalence ratio. The predicted chemiluminescent intensity was most sensitive to the rate constant of the reaction, , in bot...
139 citations
TL;DR: In this paper, a detailed kinetic scheme was compiled which closely predicts properties of mixtures of methanol, oxygen, and inert for a variety of experimental configurations and conditions and was tested against experimental data for the propagation speeds and structure of laminar flames as well as the species concentration evolutions in flow reactors, static reactors, and shock tubes.
Abstract: An experimental and numerical study of methanol kinetics has been conducted. A detailed kinetic scheme was compiled which closely predicts properties of mixtures of methanol, oxygen, and inert for a variety of experimental configurations and conditions. The scheme incorporates the most recent kinetic information and was tested against experimental data for the propagation speeds and structure of laminar flames as well as the species concentration evolutions in flow reactors, static reactors, and shock tubes. The laminar flame speeds of atmospheric methanol/air mixtures were determined using the counter-flow flame technique over extensive lean-to-rich fuel concentration ranges and for initial mixture temperatures ranging from 318 to 368 K., while the experimental data on the laminar flame structure and from reactors and shock tubes were obtained from the literature. The scheme compiled herein includes the detailed C1, C2, and methanol submechanisms and yields close agreement with all of the experi...
138 citations
TL;DR: In this article, the nonsteady behavior of counterflow diffusion hydrogen-air flames is studied using a finite difference implicit method and a complex kinetics model, and the flame responses to step and sinusoidal strain rale variations are obtained for flames submitted to moderate strain rates and also to strain rates corresponding to extinction conditions.
Abstract: The nonsteady behaviour of counterflow diffusion hydrogen-air flames is studied in this article, using a finite difference implicit method and a complex kinetics model. The flame responses to step and sinusoidal strain rale variations are obtained for flames submitted to moderate strain rates and also to strain rates corresponding to extinction conditions. Frequency response curves are obtained for both cases and for different values of the equivalence ratio. The behaviour of flame characteristics like the maximum temperature, the heat release rate and typical species mass fraction profiles is examined. It is found that H2O and OH radicals change approximately like the maximum temperature while hydrogen atom H mass fraction exhibits larger excursion. The dynamics of the flame are governed by the imposed mean strain rate on one hand and by the critical extinction strain rate on the other. Far from the extinction limit the cut-off frequency is set by the mean strain rate and the flame behaviour is ...
132 citations
TL;DR: In this paper, a comprehensive kinetic/thermochemical model for the high-temperature radical chain decomposition of acetylene and the polyacetylenes is presented, which is tested against new shock tube data: time-of-flight mass spectra in C4H2/H2, mixtures over 1600-2100K and laser schlieren experiments in C2H2; covering 2700-3500 K.
Abstract: A comprehensive kinetic/thermochemical model for the high-temperature radical chain decomposition of acetylene and the polyacetylenes is presented. This mechanism is tested against new shock tube data: time-of-flight mass spectra in C4H2/H2, mixtures over 1600-2100K and laser schlieren experiments in C2H2; covering 2700-3500 K. Some earlier time-of-flight measurements on C2H2, are also modeled. The paper includes a very extensive consideration of species thermochemistry, and the model is in full accord with the current consensus, having Δƒ H0(C2H) = 135·5kcal/mol. Entropies are computed from recent determinations of molecular parameters for C,H and from new high-level ab initio calculations for C4H reported here.Thetime-of-flight measurementssupport Δƒ H0(C2H2)= 111 kcal/mol or 28·24kcal/mol for the [C,-(C1)] group. Rate constants for the key C-H fission reactions of the acetylenes are taken from RRKM calculations calibrated against the direct measurements of dissociation in C2;H2, and C4H2:. Alt...
124 citations
TL;DR: In this paper, a simulation model of the axial structure of turbulent jet diffusion flames is formulated for the purpose of interpreting flame-structure measurements, based on the linear-eddy approach, incorporating spatial and temporal variation of the air entrainment rate, reflecting buoyancy effects, and an implementation of turbulent mixing using a novel stochastic representation of convective stirring in conjunction with Fick's law governing molecular diffusion.
Abstract: A simulation model of the axial structure of turbulent jet diffusion flames is formulated for the purpose of interpreting flame-structure measurements. The model, based on the linear-eddy approach, incorporates spatial and temporal variation of the air entrainment rate, reflecting buoyancy effects, and an implementation of turbulent mixing using a novel stochastic representation of convective stirring in conjunction with Fick's law governing molecular diffusion. Simulation results are compared to axial profiles of mixing-cup density measured in propane flames. The comparisons suggest that the measured Froude-number dependences reflect the combined effect of finite-rate mixing and the transition from forced to natural convection. Predictions for hydrogen flames are presented in order to assess the generality of inferences based on the propane results.
113 citations
TL;DR: In this article, it was demonstrated that water vapor, either from the ambience or generated at the flame, can freely condense at the droplet surface and subsequently dissolve into the interior.
Abstract: The vaporization and combustion of freely-falling methanol and ethanol droplets in dry and humid environments has been studied experimentally. From time-resolved data of the droplet size and composition, it is demonstrated that water vapor, either from the ambience or generated at the flame, can freely condense at the droplet surface and subsequently dissolve into the droplet interior. The associated condensation heat release and dilution of the droplet alcohol concentration can significantly modify the gasification behavior from that of the d2-law. Specifically, droplet gasification is characterized by an initial period during which the gasification rates of methanol and the entire droplet are enhanced due to the condensation heat release, an intermediate period during which water vapor still condenses although the overall droplet gasification rate is retarded due to water build-up, and a final, slow-gasification period during which the initially condensed water is gasified. The stucy further de...
93 citations
TL;DR: In this article, the extinction and ignition limits of strained diffusion flames are examined for different values of the fuel-air ratio and for a set of air stream temperatures, and it is shown that the critical extinction strain rate is ten times that found for an air stream at room temperature.
Abstract: Structures, extinction and ignition limits of strained diffusion flames are examined. The influence of the oxidizer stream temperature is specifically considered. Calculations are performed for diffusion flames formed by a counterflow of diluted hydrogen and air. The air temperature differs from the hydrogen temperature. The reactive flow equations are solved numerically by employing Newton iterations and adaptive continuation techniques. The model includes detailed transport and complex kinetics. Flame structures, extinction and ignition limits and characteristic flame response curves are determined for different values of the fuel-air ratio and for a set of air stream temperatures. It is shown that this last parameter strongly affects the conditions producing extinction. For an air stream temperature of 100OK, the critical extinction strain rate is ten times that found for an air stream at room temperature It is also found that a temperature exists beyond which combustion always takes place wha...
85 citations
TL;DR: In this paper, a high temperature CO2/CO mixture is experimentally studied and it is shown that the sharp transition from vapor-phase to heterogeneous combustion occurs with increasing CO content in the atmosphere.
Abstract: Magnesium is known to be a perspective fuel for engines which could use CO2 from the atmospheres of Mars and Venus as an oxidizer. Combustion of magnesium samples introduced into a high temperature CO2/CO mixture is experimentally studied. Measurements of the burning time as well as visual observations and spectral analysis of the flame show that the sharp transition from vapor-phase to heterogeneous combustion occurs with increasing CO content in the atmosphere. Study of the condensed products and thermodynamic analysis of magnesium particle combustion in CO, and CO indicate that the gas-phase reaction Mg + CO2 = MgO + CO and the heterogeneous reaction Mg + CO = MgO + C occur during combustion in C02 whereas during combustion in CO the heterogeneous reaction occurs only. Competition of the gas phase reaction, the heterogeneous reaction and the metal evaporation is the reason for the sharp transition from one to another regime.
TL;DR: In this article, the characteristics of metal capture by various bed sorbents during fluidized bed incineration of wastes containing lead chloride were evaluated in a 76.2 mm ID fluidised bed of sand, limestone and aluminum oxide.
Abstract: The emission of toxic metals during the incineration of solid wastes containing metals presents potential environmental and health hazards. Some of the metals in the effluent gases are of submicron size which conventional air pollution control devices may not always effectively collect. One of the alternative control technologies for heavy metal emissions is to use sorbents to capture metals through various mechanisms during incineration. Of the available incineration systems, the fluidized bed incinerator appears to be suitable for this purpose. The objective of this work was to experimentally study the characteristics of metal capture by various bed sorbents during fluidized bed incineration of wastes containing lead chloride. Experiments were carried out in a 76.2 mm ID fluidized bed of sand, limestone and aluminum oxide. Combustible test materials contaminated with lead chlorides were incinerated in the bed with different sorbents under different incineration conditions. The observed results ...
TL;DR: In this paper, a new Q-formalism of Bimolecular Quantum Quantum-RRK theory was proposed for reactions of C2H3 + 02 by using a new BIMO model.
Abstract: Kinetics and products are predicted for reactions of C2H3 + 02 by using a new Q-formalism of Bimolecular Quantum-RRK. theory. Association forms a chemically activated adduct, ( C2H3OO), which may isomerize one or more times to other hot isomers before decomposing or being stabilized. At low temperatures and pressures, HCO + H2CO are predicted to be formed without thermal intermediates, as observed by Gutman and co-workers. At atmospheric pressure, however, collisional stabilization of C2H3OO and its subsequent thermal reactions can be important. Glyoxal + H and C2H2 + HO, are predicted to be the next most important products of C2H3 + 02 association. All of these rate constants decrease significantly at high temperatures where ( C2H3 OO)* reverts to reactants preferentially. Above 1500 K, Ihe dominant products could be C2H2 + H02 formed directly by pressure-dependent H-atom transfer.
TL;DR: In this article, the spectral optical constants of two important hydrocarbon fuels, heptane (C7H16) and decane(C10H16), were determined using a FT-IR spectrometer.
Abstract: The objective of the present work is to experimentally determine the spectral optical constants of two important hydrocarbon fuels, heptane (C7H16) and decane (C10H16). This quantitative information is important for characterizing the absorption behavior of the species, and for analyzing spray combustion processes by laser diagnosis technique. The normal transmittance data of the hydrocarbon species are measured in the wavelength region of 2.5μ to 15μm at various pathlengths using a FT-IR spectrometer. The spectral refractive index, n, and extinction coefficient, k, which give a best fit of analytical trans-mittances to the experimental ones, are tabulated for convenient use.
TL;DR: In this paper, an open-loop and closed-loop active control system was used to suppress combustion instability in a dump combustor with high frequency acoustic forcing to break down the coherence of large-scale vortical structures, thus reducing the periodic heat release which excites the instability.
Abstract: Suppression of combustion instability in a dump combustor was demonstrated with open-loop and closed-loop active control systems. Pressure oscillations and CH-emission sensors were used to monitor the combustion process. Acoustic drivers were used to modulate the fuel and modify the shear layer at the dump. The open-loop active-control system applied high frequency acoustic forcing to break down the coherence of the large-scale vortical structures, thus reducing the periodic heat release which excites the instability. The closed-loop controller used the CH-emission signal or the pressure fluctuations, after filtration, to lock the acoustic excitation at various relative phase angles. The pressure locking was more effective in suppressing the oscillations at a relative phase angle range of 250-330°. The reduced oscillations were observed by both CH and pressure sensors. The CH locking was significantly less effective relative to the pressure locking, but had a similar range of phase angles in whic...
TL;DR: In this paper, the thermal decomposition of methyl chloride in hydrogen/oxygen mixtures and argon bath gas was carried out at 1 atmosphere pressure in tubular flow reactors.
Abstract: The thermal decomposition of methyl chloride in hydrogen/oxygen mixtures and argon bath gas was carried out at 1 atmosphere pressure in tubular flow reactors. CH3Cl, intermediate, and final products were analyzed over the temperature range 1098 to 1273 K, with average residence times of 0.2 to 2.0 s. A detailed kinetic reaction mechanism based upon fundamental thermochemical and kinetic principles, Transition State Theory and evaluated literature rate constant data was developed to explain and understand the data. The model results show good fits to methyl chloride, intermediate, and final products species profiles with both temperature and time of reaction. The model also fits the data on HCl inhibited oxidation of CO presented in the companion paper by Roesler et al. Reactions showing high sensitivity to inhibition of CO oxidation were identified. The results indicate that the reaction OH + HCl → H2O + Cl is an important source of OH loss. This decrease in OH strongly effects CO burnout. The re...
TL;DR: In this paper, the curvature of turbulent premixed flame fronts is quantified over a range of turbulence conditions using a curve-tracing difference formula with interval length of the order of the inner cutoff scale.
Abstract: The curvature of turbulent premixed flame fronts is an important spatial property that needs to be quantified over a range of turbulence conditions. In this study, measurements of flamelet curvature along with orientation statistics for u'/ SL = 1.42-5.71 are obtained from OH planar laser-induced fluorescence images of the flame boundary by applying a curve-tracing difference formula with interval length of the order of the inner cutoff scale. Use of this particular interval length is essential for accurate tracing of the flame boundary with implicit filtering of extraneous noise that can introduce significant errors in the curvature measurements. The distributions of flamelet curvature are found to be symmetric with respect to the zero mean, while the variance increases with increasing u'/SL. These distributions can be approximated by Gaussian distribution functions. The positive and negative mean curvatures show a nearly square-root dependence on u'/SL whereas the mean flamelet radius of curvat...
TL;DR: In this article, the characteristics of burning and non-burning gas jets issued from elliptic and circular nozzles in a low velocity concentric air stream is presented. But the results showed that the elliptic nozzle flames were found to have lower flame stability, higher temperatures, lower soot concentration, and lower flame radiation than those of the circular nozzle flames.
Abstract: An experimental study of the characteristics of the burning and nonburning gas jets issued from elliptic and circular nozzles in a low velocity concentric air stream is presented. Propane mixed with nitrogen was used as the jet fluid. The diameter of the circular nozzle was 9.5 mm and the elliptic nozzle had the same exit area as that of the circular nozzle and an aspect ratio (major axis/minor axis) of 3:1. The liftoff and reattachment behavior, temperature profiles, concentration profiles of fuel, oxygen, carbon dioxide, carbon monoxide, nitric oxide, and soot, flame radiation, opacity of the flame samples, the profiles of the streamwise component of the mean velocity, and r.m.s. value of the velocity fluctuation in the streamwise direction were measured. The elliptic nozzle flames were found to have lower flame stability, higher temperatures, lower soot concentration, and lower flame radiation than those of the circular nozzle flames. The nitric oxide concentration in the mid-flame region was ...
TL;DR: In this paper, the effects of scales smaller than the laminar flame thickness (δ) on the turbulent flame speed were investigated and it was concluded that the effect of small scales on turbulent flames is probably significant for most flames.
Abstract: Yakhot's turbulent flame speed model is extended to include the effects of scales smaller than the laminar flame thickness (δ). An expression for the turbulent flame speed (ST) as a function of the turbulence intensity (u') and turbulent Reynolds number is derived. Good qualitative and fair quantitative agreement with experiment is obtained. It is found that at moderately high u', the small scales act to increase 5rover a “thin” flame at the same u' and that at very high u' these scales may actually cause a decrease in ST. In agreement with recent experimental observations, it is concluded that the effect of scales smaller than δ are probably significant for most flames at sufficiently high u'. It is argued that the high Reynolds number flames are in some respects simpler than low and intermediate Reynolds number flames because the application of the methods of statistical physics are possible in the former case.
TL;DR: In this paper, the 2D thennal-diffusive model of premixed flames is solved numerically and the growth rates of the thermaldiffusive instability are compared to the linear theory.
Abstract: The 2-D thennal-diffusive model of premixed flames is solved numerically. The growth rates of the thermal-diffusive instability are compared to the linear theory. It is shown that the discrepancy, although large (a relative error than can be larger than 100%), behaves like O(I/β) as expected by asymptotics (β being the reduced activation energy or Zeldovich number). We additionally present results far in the non-linear domain. They exhibit turbulent behaviour which are qualitatively similar to the dynamical properties of the Kuramoto-Sivashinsky model-equation.
TL;DR: In this article, a phenomenological extension of the Michelson-Sivashinsky evolution equation is proposed for weakly wrinkled premixed flames, which possesses an infinite number of closed-form solutions, the mathematical relevance of which is checked through comparisons with the results or accurate numerical, spectral integrations.
Abstract: Synthesizing several analytical results on weakly wrinkled premixed flames, we suggest a simple, phenomenological extension of the Michelson-Sivashinsky evolution equation. It possesses an infinite number of closed-form solutions, the mathematical relevance of which is checked through comparisons with the results oraccurate numerical, spectral integrations. Unexpectedly enough, the proposed equation seems to be quantitatively compatible with the few pre-existing, independant results on markedly wrinkled steady fronts.
TL;DR: In this paper, the thermal decomposition of 1.0% chloroform in argon bath gas was studied to determine important chlorocarbon reaction pathways in pyrolysis.
Abstract: Chloroform was used as a model chlorocarbon system with high Cl/H ratio to investigate the thermal decomposition processes of chlorocarbons in pyrolytic reaction environments. The thermal decomposition of 1.0% chloroform in argon bath gas was studied to determine important chlorocarbon reaction pathways in pyrolysis. The reactions were studied in tubular flow reactors at a total pressure of 1 atm with residence times of 0.3-2.0 sec in the temperature range 535-800°C. A detailed kinetic reaction mechanism to describe the important features of products and reagent loss was developed. The mechanism is based on thermochemical principles and accurately describes the overall reaction process. We determine that the primary decomposition reaction pathway for chloroform is: CHCl3 → HCl +: CCl2 in the above temperature regime by combined experiment and modeling studies. High pressure limit rate constants obtained in this work for initially important decomposition of chloroform were determined as: A(1/sec.)...
TL;DR: In this article, a detailed kinetic model for moist CO oxidation chemistry inhibited by HCl is developed and analyzed by sensitivity and reaction flux analyses, validated against experimental data obtained from an atmospheric pressure flow reactor.
Abstract: A detailed kinetic model for moist CO oxidation chemistry inhibited by HCl is developed and analyzed by sensitivity and reaction flux analyses. The model is validated against experimental data obtained from an atmospheric pressure flow reactor. The kinetics were studied experimentally and numerically with dilute mixtures of CO (∼ 1%), H2O (∼ 0.5%), O2 and HCl reacting in N2 at a temperature near 1000 K. The effect of increasing the Cl/H ratio was investigated by increasing HCl concentrations from 0 to 200 ppm while the effect of excess O2 was studied by varying the fuel oxidizer equivalence ratio from 1.0 to 0.33. The results showed that small quantities of HCl inhibit CO oxidation and that increasing O2 concentrations to stoichiometric mixtures further decreases the oxidation rate, a counter intuitive result. The model predictions for CO, O2, CO2 and temperature profiles agree well with the experimental results (within 10%). Thus the inhibiting characteristics of HCl are well described. However,...
TL;DR: In this article, the authors describe a one-dimensional model to predict the time required for the water sublayer to start to boil (TWSB), including the unsteady term in the thermal energy equation, along with conduction and in-depth absorption of radiation terms.
Abstract: This study is the continuation of a previous study (Part I) on boilover of liquid fuels supported on water. Previously we designed a small-scale pool-fire apparatus and tested seventeen different (single and multicomponent) liquid fuels on water. Based on this established data, in this paper we describe a one-dimensional model to predict the time required for the water sublayer to start to boil (TWSB). The model includes the unsteady term in the thermal energy equation, along with conduction and in-depth absorption of radiation terms. To fully implement the model, radiation absorption was measured for toluene and Alberta Sweet crude oil as a function of fuel-layer thickness. The model calculation predicts the formation of inverse temperature profiles in the liquid due to the effect of in-depth absorption. Occurrence of the predicted Rayleigh convection in the fuel layer is confirmed using holographic inter-ferometry, and its effect on TWSB is estimated by comparing the model calculations with the...
TL;DR: In this article, the rotational anti-Stokes Raman scattering of pure rotational transitions (CARS) was used to measure temperature profiles in premixed, sooting ethylene flames at atmospheric pressure by probing the nitrogen gas.
Abstract: Coherent anti-Stokes Raman scattering of pure rotational transitions, rotational CARS, is demonstrated as an efficient method for temperature determination in sooting flames. The dual broadband CARS approach was used to measure temperature profiles in premixed, sooting ethylene flames at atmospheric pressure by probing the nitrogen gas. The recorded spectra were of equally high quality in non-sooting and sooting flames with volume fractions of soot of up to 7 x 10 7 cm3 soot/cm3The advantages of rotational CARS in comparison with several other techniques for the measurement of temperatures in sooting flames, and the general applicability of the technique to different combustion conditions, are discussed. Potential limitations in the application of rotational CARS to sooting flames that are more heavily sooting than the ones investigated in this study, are outlined. © 1992, Taylor & Francis Group, LLC. All rights reserved. (Less)
TL;DR: In this article, an experimental apparatus was constructed which allows investigation of the vaporization behavior of metal contaminants during incineration of their host substrate, and comparisons were made between equilibrium predictions and experimental observations for a number of different melals in chlorinated, inert, and reducing environments between 150°C and 650°C.
Abstract: An experimental apparatus was constructed which allows investigation of the vaporization behavior of metal contaminants during incineration of their host substrate. Comparisons were made between equilibrium predictions and experimental observations for a number of different melals in chlorinated, inert, and reducing environments between 150°C and 650°C. The equilibrium predictions for Pb vaporization were found to show the greatest deviation from experimental observations. Comparisons showed that a knowledge of elements associated with the initial metal species, as well as omission of PbCl4 from the calculations, can be important for the equilibrium predictions. Experimental results showed that the formation of volatile PbCl4 predicted by equilibrium was not kinetically favorable under the conditions studied. Subsequent vaporization studies involving PbCl2 deposited on a silica substrate demonstrated an influence of initial concentration on the amount of Pb vaporization observed. The extent of va...
TL;DR: In this paper, an optical method for monitoring the products of combustion, particularly for the detection of upset conditions in the incineration of hazardous waste, is disclosed, where the combustion is monitored via infrared absorption using tunable diode lasers (TDLs).
Abstract: An optical method for monitoring the products of combustion, particularly for the detection of upset conditions in the incineration of hazardous waste, is disclosed. On-line detection of upsets is extremely important to avoid sending untreated waste out the stack plume and to avoid the formation of hazardous products of incomplete combustion, such as dioxins. Small hydrocarbons are the strongest candidates for in situ monitoring of combustion efficiency. The combustion is monitored via infrared absorption using tunable diode lasers (TDLs).
TL;DR: Fluorescence spectra were obtained in laminar, gaseous, rich premixed and diffusion flames employing different harmonics of a pulsed Nd: YAG laser as discussed by the authors.
Abstract: Fluorescence spectra were obtained in laminar, gaseous, rich premixed and diffusion flames employing different harmonics of a pulsed Nd: YAG laser. Spectra obtained with the fourth harmonic at λ0 = 266 nm exhibit a peak in the u.v. at λ = 320 nm and a broader one in the visible with a maximum beyond 400 nm. The relative role of these two features has been followed in rich premixed flames with different C: O ratios and heights above the burner and along the radius of a cylindrical, coflowing diffusion flame. The u.v. fluorescence detected in our flames should be attributed to structures containing no more than two aromatic rings, while the fluorescence in the visible is attributed to larger aromatic structures. Fluorescence and absorption spectra obtained from the different fractions of the material sampled into the flames showed qualitative agreement with the “in silu” spectra. Fluorescence spectra in the visible, originating from structures heavier than 300a.m.u., has been also detected in the s...
TL;DR: In this article, a theoretical analysis of the linear burning response of an homogeneous solid propellant to pressure fluctuations is presented, which takes into account the non-steady effects of the gas phase in a systematic way.
Abstract: This paper presents a theoretical analysis of the linear burning response of an homogeneous solid propellant to pressure fluctuations. The major contribution of this work is to take into account the non-steady effects of the gas phase in a systematic way and thus, eliminate the strong limitation of previous analysis in which the gas-phase is assumed to respond in a quasi-steady manner. Two different response mechanisms are exhibited depending on the frequency range. In agreement with the well known quasi-steady theory, the low frequency response is mainly controlled by the thermal relaxation in the solid phase and is triggered through the pressure dependence of the prefactors in the pyrolysis and burning laws. At high frequencies, the gas temperature fluctuations associated with pressure oscillations, are shown to introduce a new response mechanism of the burning rate independent of the pressure exponents. This response mechanism involves the structure of the gaseous flame. The resulting vibrator...
TL;DR: In this article, a detailed characterization of methanol spray produced by an air-assist atomizer with swirling atomizing air has been conducted, including measurements of drop size, velocity, gas phase velocity, and concentration of hydrocarbons within the spray.
Abstract: A detailed characterization of a methanol spray produced by an air-assist atomizer with swirling atomizing air has been conducted. This study is the third of a series which examines the structure of sprays produced by a standardized atomizer which can be operated in three modes, pressure swirl, non-swirling air-assist, and swirling air-assist. Measurements of drop size and three components of velocity, three components of the gas phase velocity, the concentration of hydrocarbons within the spray, and time resolved droplet measurements are obtained at axial locations of 7·5, 15, 25, 35, 50, 75, and 100 mm. These measurements are obtained for both reacting and non-reacting cases. In addition, the atomizing air flow in the absence of the spray is characterized. Primary observations from the present study are that (1) the presence of the drops alters the structure of the gas phase turbulence, including the degree of isotropy, (2) the presence of reaction strongly impacts the axial and radial velocity...