Major Gas Species Concentrations Research Articles

Volcanic gas emissions from Taftan and Damavand, the Iranian volcanoes

Volcanic gas sampling and SO2 flux measurements were performed on Taftan volcano (3920 m height, SE Iran, Makran volcanic arc) and Damavand volcano (5610 m height, Northern Iran, Alborz Mountains). Both volcanoes possess near-summit fumarolic fields with moderately intensive gas jets and temperatures up to 160 °C (Taftan) and 175 °C (Damavand). Gases of both volcanoes contain (mmol/mol): H2O (910–930), CO2 (50–80), SO2 (3–7), H2S (2–5.5), HCl (5–8.2) and HF (0.1–0.13). Both volcanoes are also similar in terms of minor gas species (mmol/mol): He (0.0005–0.0011), H2 (0.00077–0.0046), N2(ex) (0.15–0.30) and Ar(ex) (0.0006–0.0012), where subscript “ex” denotes non-atmospheric fraction. δD–δ18O systematics has shown that Damavand fumarolic gases contain 60–65% of magmatic fraction whereas the Taftan emissions correspond to almost pure magmatic (“andesitic”) vapor. Low amount of nitrogen in Taftan gases and its isotopic composition may be explained by low input of nitrogen-containing organic matter with the subducting slab due to specific geometry of the Makran subduction zone, namely, by the presence of an accretionary prism of a considerable size. The origin of high CH4 content in Damavand gases and very low concentrations of C2H6 and higher hydrocarbons (0.65 mmol/mol; CO2/CH4 ~ 80; CH4/C2H6 ~ 104) is unclear. Fumaroles of Taftan volcano are poor in CH4, similar to many other arc volcanoes (CO2/CH4 ~ 105). 3He/4He isotopic composition expressed as R/Ra was measured at 7.0–7.5 for Taftan and 6.65 for Damavand, corresponding to the CO2/3He ratio of ~1.0E+10. The δ34S of the total sulfur is +7.6 ± 2‰ (2σ) for Taftan fumaroles and + 8.1 ± 2‰ (2σ) for Damavand fumaroles; δ13C (CO2) is −5.9 ± 2.0‰ (Damavand) and − 4.3 ± 0.15‰ (Taftan). Concentrations of major gas species (H2O/CO2/S/HCl ratios) and isotopic data (R/Ra, CO2/3He, δ34S) show that the volcanic gas composition on both volcanoes have a distinct arc signature. This conclusion is especially important for the intraplate Damavand volcano, which has an uncertain tectonic affinity but according to the latest geochemical studies was considered having hotspot/rift origin. Mini-DOAS measurements of the SO2 fluxes showed 20 ± 12 t/d SO2 at Taftan and 43 ± 20 t/d SO2 at Damavand, which places both volcanoes as small SO2 emitters.

Ash deposit formation during the combustion of pulverized grape pomace in a drop tube furnace

This article concentrates on the ash deposit formation during the combustion of pulverized grape pomace in a drop tube furnace. All experiments were conducted for a wall drop tube furnace temperature of 1200 °C. Initially, axial measurements of temperature, major gas species concentrations and particle burnout were obtained for a representative drop tube furnace operating condition. These measurements allowed to establish the drop tube furnace axial position to place a deposition probe, fitted with a removable stainless steel capsule, to study the ash deposit formation. Subsequently, detailed data on ash deposit formation rates were obtained for seven probe exposition times between 2 and 14 h. Finally, deposit samples for all exposition times were analysed on a scanning electron microscope equipped with an energy dispersive X-ray detector. Important distinct features of the present study include the examination of the temporal evolution of the deposit characteristics, such as their sintering degree, which is critical to assess the need for boiler cleaning, and the method of analysis of the deposits chemical composition. It is concluded that the sintering degree of the deposits increased with the probe exposition time and for exposition times above 8 h, the deposits are very difficult to remove. It is also observed that the impact of the probe exposition time in the concentrations of potassium, phosphorus and magnesium is marginal, and that the oxygen concentration decreases as the probe exposition time increases, while the opposite behavior is observed for calcium and silicon. Overall, the results reveal that the use of this biomass residue in industrial combustion systems may pose severe operational and maintenance problems, requiring frequent boiler cleaning.

Comparison of CFD Simulations with Measurements of Gaseous Sulfur Species Concentrations in a Pulverized Coal Fired 1 MWth Furnace

High temperature corrosion is a major issue in coal fired power plants. Gaseous sulfur species are one of the main causes of furnace wall corrosion. In order to take effective countermeasures, the identification of exposed furnace wall regions is necessary, which can be achieved by 3D-CFD simulations coupled with detailed sulfur and combustion chemistry. A model for the release of sulfur species during coal combustion, which is based on the mineral matter transformation of sulfur bearing minerals under coal combustion conditions, has been developed and is to be presented in this study. CFD simulations of a 1 MWth combustion chamber fired with pulverized hard coal have been carried out. Measurements of gas concentrations have been performed at different heights and radial positions as well as at the exit of the combustion chamber. The results of the simulations are in good agreement with measured concentrations of major gas species and sulfur species.

Formation of Fine Particulate Matter in a Domestic Pellet-Fired Boiler

This study concentrates on the formation of fine particulate matter (PM) in a domestic pellet-fired boiler and includes a detailed characterization of the combustion process inside the combustion chamber of the boiler. Measurements of local mean gas temperatures, major gas species concentrations, and PM concentrations and size distributions are reported for a representative boiler operating condition. In addition, a number of selected PM samples were also morphologically and chemically characterized. The results revealed that (i) most particles present aerodynamic diameters below 1 μm, regardless of the measurement location, and the mass size distributions peak in the size range of 50–130 nm; (ii) early in the flame, the PM size distributions present a bimodal size distribution, but this attribute vanishes as the final stages of the combustion process are approached; (iii) soot particles are rapidly formed early in the combustion process, but these carbon-rich particles also oxidize rapidly in the near burner region; (iv) the aerodynamic diameter corresponding to the maximum amount of particles increases slightly from the fuel bed until ≈4/5 of the combustion chamber height; (v) for a given measurement location and particle sizes below 1 μm, the PM chemical composition varies marginally among size ranges, indicating that the existing chemical compounds tend to form different size aggregates of similar composition; (vi) the element mass concentration varies according to the measurement location; early in the combustion process, the PM is dominated by carbon, with smaller amounts of O and Si, while in the final stages of the combustion process, the PM composition is dominated by inorganic material; and (vii) large fractions of the alkali metals are present as chlorides in the fine PM, and small fractions of the alkalis are present as sulfates.

Experimental evaluation of the performance of a flameless combustor

The aim of this study was to investigate experimentally the flameless oxidation phenomena. Experiments have been performed in a small-scale combustor fired with methane, and include detailed measurements of local mean temperatures and concentrations of major gas species for four representative combustor operating conditions, and flue-gas measurements for 27 operating conditions to quantify the combustor performance as a function of the excess air coefficient, inlet air velocity, fuel thermal input and preheat temperature of the combustion air. It was demonstrated that for the present combustor it is possible to establish flameless conditions over a wide range of operating conditions. The detailed in-combustor data show that the temperature and the O2 mole fraction fields are relatively uniform, and that the maximum mean temperatures reached throughout the combustion chamber are relatively moderate, below 1500 °C, even under conditions in which the level of preheating of the combustion air is relatively high. The flue-gas data reveal that NOx emissions are always very low regardless of the combustor operating conditions. However, the CO and HC emissions, and thus the combustion efficiency, are strongly affected by the levels of excess air and preheating of the combustion air. It was found that the combustion efficiency correlates reasonably well with the parameter (Tair/Tfuel)×(m˙fuel/m˙air), varying linearly with it if its value is below ≈0.1 and remaining equal to approximately 100% otherwise.

Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames

The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and 0) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and 02 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

Soot formation in laminar acetylene/air diffusion flames at atmospheric pressure

The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation—O 2, CO 2, H 2O, O, and OH—are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

Structure of the soot growth region of laminar premixed methane/oxygen flames

The structure of the soot growth region of laminar premixed methane/oxygen flames (fuel-equivalence ratios of 1.60 - 2.77) was studied both experimentally and computationally. Measurements were carried out in flames stabilized on a flat flame burner operated at standard temperature and pressure, and included velocities by laser velocimetry, soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, major gas species concentrations by sampling and gas chromatography, and hydrogen atom concentrations by the Li/LiOH technique in conjunction with atomic absorption to find the proportion of free lithium in the flames. The measured concentrations of major gas species were in reasonably good agreement with predictions based on the detailed mechanisms of Leung and Lindstedt, and Frenklach and coworkers. The measurements also confirmed predictions of both these mechanisms that H-atom concentrations are in local thermodynamic equilibrium throughout the soot growth region even through the concentrations of major gas species are not. Thus, present findings support recent evaluations of the hydrogen-abstraction/carbon-addition (HACA) soot growth mechanism in similar flames, where the approximation that H-atom concentrations were in local thermodynamic equilibrium was adopted, based on predictions using the two mechanisms, due to the absence of direct H-atom concentration measurements.

Structure of the soot growth region of laminar premixed methane/oxygen flames

The structure of the soot growth region of laminar premixed methane/oxygen flames (fuel-equivalence ratios of 1.60–2.77) was studied both experimentally and computationally. Measurements were carried out in flames stabilized on a flat flame burner operated at standard temperature and pressure, and included velocities by laser velocimetry, soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, major gas species concentrations by sampling and gas chromatography, and hydrogen atom concentrations by the Li/LiOH technique in conjunction with atomic absorption to find the proportion of free lithium in the flames. The measured concentrations of major gas species were in reasonably good agreement with predictions based on the detailed mechanisms of Leung and Lindstedt, and Frenklach and coworkers. The measurements also confirmed predictions of both these mechanisms that H-atom concentrations are in local thermodynamic equilibrium throughout the soot growth region even through the concentrations of major gas species are not. Thus, present findings support recent evaluations of the hydrogen-abstraction/carbon-addition (HACA) soot growth mechanism in similar flames, where the approximation that H-atom concentrations were in local thermodynamic equilibrium was adopted, based on predictions using the two mechanisms, due to the absence of direct H-atom concentration measurements.

99/00813 Structure of laminar permanently blue, opposed-jet ethylene-fueled diffusion flames

The structure and state relationships of laminar soot-free (permanently blue) ethylene-fueled diffusion flames at various strain rates were studied both experimentally and computationally using an opposed-jet configuration. Measurements of gas velocities, temperatures, and compositions were carried out along the stagnation stream line. Corresponding predictions of flame structure were obtained, based on numerical simulations using several contemporary reaction mechanisms for methane oxidation. Flame conditions studied included ethylene-fueled opposed-jet diffusion flames having stoichiometric mixture fractions of 0.7 with measurements involving strain rates of 60-240/s and predictions involving strain rates of 0-1140/s at normal temperature and pressure. It was found that measured major gas species concentrations and temperature distributions were in reasonably good agreement with predictions using mechanisms due to GRI-Mech and Peters and that effects of preferential diffusion significantly influence flame structure even when reactant mass diffusivities are similar. Oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures were found to exist over a broad range of strain rates, providing potential for significant computational simplifications for modeling purposes in some instances.

Structure of laminar permanently blue, opposed-jet ethylene-fueled diffusion flames

The structure and state relationships of laminar soot-free (permanently blue) ethylene-fueled diffusion flames at various strain rates were studied both experimentally and computationally using an opposed-jet configuration. Measurements of gas velocities, temperatures, and compositions were carried out along the stagnation stream line. Corresponding predictions of flame structure were obtained, based on numerical simulations using several contemporary reaction mechanisms for methane oxidation. Flame conditions studied included ethylene-fueled opposed-jet diffusion flames having stoichiometric mixture fractions of 0.7 with measurements involving strain rates of 60–240 s −1 and predictions involving strain rates of 0–1140 s −1 at normal temperature and pressure. It was found that measured major gas species concentrations and temperature distributions were in reasonably good agreement with predictions using mechanisms due to GRI-Mech (Version 1.2, 1995) and Peters (1993) and that effects of preferential diffusion significantly influence flame structure even when reactant mass diffusivities are similar. Oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures were found to exist over a broad range of strain rates, providing potential for significant computational simplifications for modeling purposes in some instances.

Soot Formation in Laminar Premixed Methane/Oxygen Flames at Atmospheric Pressure

Flame structure and soot formation were studied within soot-containing laminar premixed methane/oxygen flames at atmospheric pressure. The following measurements were made: soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, soot structure by thermophoretic sampling and transmission electron microscope (TEM), major gas species concentrations by sampling and gas chromatography, and gas velocities by laser velocimetry. Present measurements of gas species concentrations were in reasonably good agreement with earlier measurements due to Ramer et al. as well as predictions based on the detailed mechanisms of Frenklach and co-workers and Leung and Lindstedt; the predictions also suggest that H atom concentrations are in local thermodynamic equilibrium throughout the soot formation region. Using this information, it was found that measured soot surface growth rates could be correlated successfully by predictions based on the hydrogen-abstraction/carbon-addition (HACA) mechanisms of both Frenklach and co-workers and Colket and Hall, extending an earlier assessment of these mechanisms for premixed ethylene/air flames to conditions having larger H/C ratios and acetylene concentrations. Measured primary soot particle nucleation rates were somewhat lower than the earlier observations for laminar premixed ethylene/air flames and were significantly lower than corresponding rates in laminar diffusion flames, for reasons that still must be explained.

Experimental estimation of thermal expansion and vorticity distribution in a buoyant diffusion flame

The flow induced by buoyant diffusion flames results from thermal expansion caused by heat release and vorticity generated because of density gradients in the flame. The thermal expansion source induces a potential velocity field, and the vorticity induces a solenoidal velocity field. Baum and McCaffrey's technique for the calculation of fire-induced flow field requires specifications of thermal expansion and vorticity source terms. We estimate the thermal expansion using the laminar flamelet method in conjunction with measurements of major gas species concentrations. Mixture fractions are calculated based on the major species concentration data, and gradients of mixture fraction are obtained from the curve fits to the radial profiles of mixture fractions. The temperature, density, and mass diffusivity of the gases are determined using laminar flamelet state relationships from OPPDIF simulations of a natural gas/air diffusion flame. These quantities are needed for estimating the source term for thermal expansion. The mean velocity field is measured using particle imaging velocimetry. The mean vorticity is obtained by differentiating this field using a finite difference. Near the burner surface, the vorticity components based on the axial and radial velocity gradients are approximately equal. A few centimeters from the burner surface, the component involving the axial velocity becomes dominant. We have computed the fire-induced flow field using the method of Baum and McCaffrey in conjunction with the present source term measurements. The results of these computations agree reasonably well with experimental data.

Soot formation in laminar premixed ethylene/air flames at atmospheric pressure

Soot formation was studied within laminar premixed ethylene/air flames (C/O ratios of 0.78–0.98) stabilized on a flat-flame burner operating at atmospheric pressure. Measurements included soot volume fractions by both laser extinction and gravimetric methods, temperatures by multiline emission, soot structure by thermophoretic sampling and transmission electron microscopy, major gas species concentrations by sampling and gas chromatography, concentrations of condensable hydrocarbons by gravimetric sampling, and velocities by laser velocimetry. These data were used to find soot surface growth rates and primary soot particle nucleation rates along the axes of the flames. Present measurements of soot surface growth rates were correlated successfully by predictions based on typical hydrogen-abstraction/carbon-addition (HACA) mechanisms of Frenklach and co-workers and Colket and Hall. These results suggest that reduced soot surface growth rates with increasing residence time seen in the present and other similar flames were mainly caused by reduced rates of surface activation due to reduced H atom concentrations as temperatures decrease as a result of radiative heat losses. Primary soot particle nucleation rates exhibited variations with temperature and acetylene concentrations that were similar to recent observations for diffusion flames; however, nucleation rates in the premixed flames were significantly lower than in the diffusion flames for reasons that still must be explained. Finally, predictions of yields of major gas species based on mechanisms from both Frenklach and co-workers and Leung and Lindstedt were in good agreement with present measurements and suggest that H atom concentrations (relevant to HACA mechanisms) approximate estimates based on local thermodynamic equilibrium in the present flames.

Soot formation in hydrocarbon/air laminar jet diffusion flames

Soot processes along the axes of round laminar jet diffusion flames were studied, considering ethane, propane, n-butane, ethylene, propylene, and 1,3-butadiene burning in air at pressures of 25–99 kPa. Measurements included soot volume fractions, temperatures, soot structure, concentrations of major gas species and gas velocities. As distance increased along the axes of the flames, significant soot formation began when temperatures reached roughly 1250 K and fuel decomposition yielded acetylene, and ended when hydrocarbon concentrations became small at fuel-equivalence ratios of roughly 1.14. Soot growth rates were higher than earlier observations within acetylene-fueled laminar jet diffusion flames and premixed flames, which were correlated in terms of acetylene concentrations alone; this effect was attributed to either parallel soot growth channels due to the presence of significant concentrations of light hydrocarbons other than acetylene (mainly ethylene and methane) or to enhanced soot surface reactivity caused by the presence of these hydrocarbons. The present and previous soot growth data are best correlated using parallel acetylene and ethylene collision efficiencies of 0.0030 and 0.014, respectively. In contrast, present soot nucleation rates were correlated as a first-order acetylene reaction alone, with reaction parameters nearly identical to earlier findings in laminar acetylene/air diffusion flames, e.g., an activation energy of 35 kcal/gmol.

Hydrodynamic suppression of soot emissions in laminar diffusion flames

Effects of flow (hydrodynamic) properties on soot formation and oxidation in nonpremixed hydrocarbon/air flames were studied, emphasizing conditions where effects of buoyancy are small in coflowing laminar jet diffusion flames. Effects of air/fuel-stream velocity ratios were of particular interest; therefore, the experiments were carried out at reduced pressures (0.19-0.50 atm) in order to minimize effects of flow acceleration due to buoyancy. Test conditions included acetylene, propylene, and 1,3-butadiene flames burning in air with air/fuel-stream velocity ratios in the range 0.4-6.7. Measurements included laminar smoke-point properties, as well as the following flame structure properties: soot volume fractions, temperatures, soot structure, concentrations of major gas species, and velocities. The measurements showed that laminar smoke-point flame lengths can be increased, and soot emissions possibly suppressed entirely, by increasing air/fuel-stream velocity ratios. The flame structure measurements suggest that the mechanism of this effect involves the magnitude and direction of flow velocities relative to the flame sheet. In particular, large air/fuel-stream velocity ratios cause soot to form in cool and fuel-rich gases, inhibiting soot nucleation, and then to be drawn directly toward the flame sheet with a limited residence time, inhibiting soot growth, so that capabilities to complete the oxidation of soot are enhanced and the tendencies to emit soot are reduced.

Analysis of Laminar Acetylene-Air Diffusion Flames Using Reduced Reaction Mechanisms and State Relationships

Abstract In the development of state relationships much of the research has been experimental and limited to steady and lightly sooting flame configurations. This study computationally investigates soot and radiation effects on the state relationships in an unsteady, spherical, moderately sooting, acetylene/air diffusion-flame by coupling the gas phase and soot reaction mechanisms. The gas phase species concentrations are computed either by using a reduced reaction mechanism or by invoking the laminar flamelet concept. Comparisons are made between these two formulations. For moderately sooting, acetylene/air, unsteady diffusion-flames, calculations show that universality for most of the major gas species concentrations does not exist when the species are plotted in either gas phase or total mixture fraction space. In line with experimental results, defining a modified gas species mass fraction and utilizing the apparent gas phase mixture fraction extends the state relationships for most major gas species ...

Soot formation in weakly buoyant acetylene-fueled laminar jet diffusion flames burning in air

The structure and soot properties of weakly buoyant, acetylene-fueled, laminar jet diffusion flames were studied experimentally for combustion in air at pressures of 0.125–0.250 atm. Properties along the axis, where soot processes are similar to behavior within nonbuoyant diffusion flames, were emphasized. The following measurements were made: soot volume fractions using laser extinction, temperatures using both thermocouples and multiline emission, soot structure using thermophoretic sampling and analysis by transmission electron microscopy, concentrations of major gas species using sampling and analysis by gas chromatography, and velocities using laser velocimetry. As distance increased along the axis of the present acetylene-fueled flames, significant soot formation began when temperatures exceeded roughly 1250 K, and ended when fuel-equivalence ratios decreased to roughly 1.7, where the concentration of acetylene became small. This behavior allowed observations of soot growth and nucleation for acetylene concentrations of 6 × 10 −6-1 × 10 −3 kg-mol/m 3 and temperatures of 1000–2100 K. Over this range of conditions, soot growth rates were comparable to past observations of new soot in premixed flames, and after correction for effects of soot oxidation yielded essentially first-order growth with respect to acetylene concentrations with a negligible activation energy, and an acetylene/soot collision efficiency of 0.53%. Present measurements of soot nucleation rates also suggested first-order behavior with respect to acetylene concentrations but with an activation energy of 32 kcal/gmol and with rates that were significantly lower than earlier estimates in the literature. Nevertheless, uncertainties about effects of soot oxidation and age on soot growth, and about effects of surface area estimates and translucent objects on soot nucleation, must be resolved in order to adequately define soot formation processes in diffusion flames.

Combustion tests on an industrial glass-melting furnace

Local gas temperatures, local concentrations of major gas species and incident wall heat fluxes were measured in a large end-port, fuel-fired regenerative furnace for manufacture of glass containers, with a nominal output of 90 t d −1 of soda-lime glass and a specific energy consumption of 5.9 GJ t −1. Two different operating conditions were studied to investigate the effect of furnace throughput and air:fuel ratio on the heat transfer characteristics of the furnace. The measurements were performed through inspection ports in the furnace and quantified its cyclic operation as well as the three-dimensional nature of the heat transfer processes. The local wall heat fluxes were in the range 250–300 kW m −1, with maximum variations along each wall of 20%. The maximum temperatures in the flame and in the exhaust gases were 1660 and 1540 °C respectively, the latter associated with 2% excess O 2. The maximum measured concentrations of carbon monoxide varied between 5 vol.% in the flame and 0.5 vol.% at the exit of the combustion chamber. The nitrogen oxide levels were ∼ 4000 ppmv. The results provide the necessary detail to allow the validation of numerical procedures to interpolate and extrapolate the experimental information.

Coupled radiation and soot kinetics calculations in laminar acetylene/air diffusion flames

Radiation heat transfer from flames depends on the instantaneous soot volume fractions and temperatures. A coupled radiation and soot kinetics calculation in laminar acetylene/air and acetylenemethane/air diffusion flames is described. Transport equations for mass, momentum, gas-phase mixture fraction, enthalpy (sensible + chemical), soot mass fraction, and soot number density are solved. A simplified soot kinetics model incorporating nucleation, growth, oxidation, and agglomeration processes is used. The reaction rates in the simplified kinetics model depend on the temperature and the local concentrations of acetylene and oxygen. The major gas species concentrations are obtained from state relationships. The local temperature is obtained by solving the energy equation, taking radiation loss and gain and the energy exchanges associated with soot formation and oxidation into consideration. The radiative source/sink term in the energy equation is obtained using a multiray method. Since these flames radiate a substantial part of their energy, the kinetic rates associated with soot processes are strongly coupled to the energy equation. This strong coupling between radiation, and soot formation and oxidation processes is modeled for the first time. The results of the soot kinetics model are compared with measurements of soot volume fractions obtained using laser tomography. The agreement between measurements and predictions of soot volume fractions supports the present method. The predicted temperature profiles support the structure of strongly radiating flames discovered earlier.