Smoldering combustion of "incense" sticks - Experiments and modeling

This paper is concerned with the experimental and modeling studies on the smoldering rates of incense sticks as a function of ambient oxygen fraction in air, the flow velocity and size. The experimental results are obtained both for forward and reverse smolder conditions. The results are explained on the basis of surface combustion due to diffusion of oxygen to the surface by both free and forced convection supporting the heat transfer into the solid by conduction, into the stream by convection and the radiant heat transfer from the surface. The heat release at the surface is controlled by the convective transport of the oxidizer to the surface. To obtain the diffusion rates particularly for the reverse smolder, CFD calculations of fluid flow with along with a passive scalar are needed; these calculations have been made both for forward and reverse smolder. The interesting aspect of the CFD calculations is that while the Nusselt umber for forward smolder shows a clear root( Re-u) dependence ( Re-u = Flow Reynolds Number), the result for reverse smolder shows a peak in the variation with Reynolds number with the values lower than for forward smolder and unsteadiness in the flow beyond a certain flow rate. The results of flow behavior and Nusselt number are used in a simple model for the heat transfer at the smoldering surface to obtain the dependence of the smoldering rate on the diameter of the incense stick, the flow rate of air and the oxygen fraction. The results are presented in terms of a correlation for the non-dimensional smoldering rate with radiant flux from the surface and heat generation rate at the surface. The correlations appear reasonable for both forward and reverse smolder cases.

Microgravity Smoldering Combustion Of Flexible Polyurethane Foam With Central Ignition

Smoldering constitutes a significant fire risk both in normal gravity and in microgravity. This space experiment has been conducted aboard the China Recoverable Satellite SJ-8 to investigate smoldering characteristics of flexible polyurethane foam with central ignition in a forced flow of oxidizer. This configuration resulted in a combination of opposed and forward flow smolder. The microgravity experiment is rather unique in that it was performed at constant pressure, and with a relatively high ambient oxygen concentration (35% by volume). The smoldering characteristics are inferred from measurements of temperature histories at several locations along the foam sample. Particularly important is the discovery that there is a transition from smoldering to flaming near the sample end in the opposed smoldering. This transition seems to be caused by strong acceleration of the smoldering reaction. The observed transition serves to initiate a vigorous forward-propagating oxidation reaction in the char left behind by the smoldering reaction. The secondary char oxidation reaction propagates through the sample and consumes most of the remaining char. In forward flow smoldering, the oxidizer depletion by the upstream opposed smolder prevents an exothermic oxidation reaction from being established in the foam until this preceding reaction is completed. Once fresh oxidizer flows in the sample, the existing conditions are sufficient for a self-sustained forward smoldering reaction to take place.

Log smoldering after an Amazonian deforestation fire

The characteristics of log smoldering after an Amazonian deforestation fire are described. The experiment was carried out in 2001 at the Caiabi farm, near the city of Alta Floresta, state of Mato Grosso, Brazil, as part of a set of tests that have been performed in the same area since 1997. A 200 x 200m(2) test area was slashed in the beginning of June and burned on 20 August. The area contained 507 logs with diameter at breast height (DBH) higher than 10 cm, per hectare. In the day following the main burn 59 logs were found to remain smoldering, a number that corresponds to 2.9% of the total in the area. We chose 11 of the 59 logs to have their smoldering process monitored. Their diameter, moisture content and CHN dry biomass composition after the plot burn and before smoldering were determined. Other parameters such as temperature distribution while smoldering, porosity, density and mass volatilized during thermogravimetric test were also determined. Average smoldering speeds were in the range from 0.8 to 1.5 cm h(-1) for logs that smoldered without transition to the flaming regime. The average speed increased to 2.1 cm h(-1) for those logs that oscillated between smoldering and flaming. The speeds were lower overnight as compared to values determined during daytime for the same log. Higher log moisture contents were found to produce decreased speeds. Micro-porous biomass was not observed in the set of the 11 selected logs. Smoldering was observed to occur at substantial intensity in crossing of logs, with no longitudinal propagation. (C) 2003 Elsevier Ltd. All rights reserved.

Smoldering flames; adventures and emotions of a flapper,

Mode of access: Internet.

Luminescence enhancement in monoclinic CaAl2O4:Eu2+, Cr3+ nanophosphor by fuel-blend combustion synthesis

Eu2+ ion doped into a suitable host results in an efficient luminophore with engineering relevance; however stabilizing this ion in a host is known to be a challenge. Here we report a novel approach for the synthesis of efficient CaAl2O4 phosphor containing Eu2+ luminophore and Cr3+ activator. CaAl2O4:Eu2+, Cr3+ is prepared by a solution combustion (SCS) method using (i) urea, (ii) oxalyl dihydrazide (ODH) and (iii) fuel-blend (in which overall fuel to oxidizer ratio (F/O) = 1). A Multi-channel thermocouple setup is used to measure the flame temperatures to study the nature of combustion of various fuel mixtures. The variation of adiabatic flame temperature is calculated theoretically for different urea/ODH mixture ratios according to thermodynamic concept and correlated with the observed flame temperatures. Blue emission of the CaAl2O4:Eu2+ phosphor is enhanced similar to 20 times using the fuel-blend approach. Using the observed reaction kinetics, and the known chemistry of smoldering type combustion, a mechanism is proposed for the observed stabilization of Eu2+ ion in the fuel-blend case. This also explains the observed improvement in blue light emission. We show that the right choice of the fuel ratio is essential for enhancing photoluminescence (PL) emission. The PL intensity is highest for ODH lean and urea rich combination (i.e. when the ratio of ODH:urea is 1:5); measured color purity is comparable to commercial blue phosphor, BAM:Eu2+. (C) 2015 Elsevier B.V. All rights reserved.

卫星搭载聚氨酯泡沫闷烧实验

SJ-8卫星搭载闷烧实验，利用长时间微重力条件，对等压条件下聚氨酯泡沫试样中的闷烧点燃和双向传播过程进行了研究，两种气流氧气浓度分别为21％和35％，气流速度为3．1mm／s．实验结果表明，氧气浓度较小时，逆向闷烧在传播到试样末端之前将自行熄灭，同向闷烧可以自维持传播至试样末端．气流氧气浓度为35％时，逆向闷烧和同向闷烧都可自维持传播；当逆向闷烧传播至试样末端区域时反应急剧加速，导致局部发生闷烧向有焰燃烧转变；有焰燃烧进一步点燃闷烧反应留下的剩余碳，使其发生剧烈的二次氧化反应，并向下游传播直到剩余碳耗尽．实验结果为研究闷烧机理提供了基础数据，对载人航天器舱内的火灾安全具有实际意义．

Laboratory evaluation of Amazon forest biomass burning emissions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of specimen size, tray inclination and air flow rate on the emission of gases from biomass combustion

Experiments of biomass combustion were performed to determine whether specimen size, tray inclination, or combustion air flow rate was the factor that most affects the emission of carbon dioxide, carbon monoxide, and methane. The chosen biomass was Eucalyptus citriodora, a very abundant species in Brazil, utilized in many industrial applications, including combustion for energy generation. Analyses by gas chromatograph and specific online instruments were used to determine the concentrations of the main emitted gases, and the following figures were found for the emission factors: 1400 ± 101 g kg-1 of CO2, 50 ± 13 g kg-1 of CO, and 3.2 ± 0.5 g kg-1 of CH4, which agree with values published in the literature for biomass from the Amazon rainforest. Statistical analysis of the experiments determined that specimen size most significantly affected the emission of gases, especially CO2 and CO. •Statistical analysis to determine effects on emission factors.•CO2, CO, CH4 emission factors determined for combustion of Eucalyptus.•Laboratory results agreed with data for Amazonian biomass combustion in field tests.•Combustion behavior under flaming and smoldering was analyzed. © 2013 Elsevier Ltd.

Quantificação de poluentes emitidos durante a queima de biomassa florestal em laboratório

Pós-graduação em Engenharia Mecânica - FEG

Comparative study for hardwood and softwood forest biomass: Chemical characterization, combustion phases and gas and particulate matter emissions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Real-time Sampling of Particulate Matter Smaller than 2.5 µm from Amazon Forest Biomass Combustion

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Carbon monoxide and related trace gases and aerosols over the Amazon Basin during the wet and dry seasons

We present the results of airborne measurements of carbon monoxide (CO) and aerosol particle number concentration (CN) made during the Balan double dagger o Atmosf,rico Regional de Carbono na Amazonia (BARCA) program. The primary goal of BARCA is to address the question of basin-scale sources and sinks of CO2 and other atmospheric carbon species, a central issue of the Large-scale Biosphere-Atmosphere (LBA) program. The experiment consisted of two aircraft campaigns during November-December 2008 (BARCA-A) and May-June 2009 (BARCA-B), which covered the altitude range from the surface up to about 4500 m, and spanned most of the Amazon Basin. Based on meteorological analysis and measurements of the tracer, SF6, we found that airmasses over the Amazon Basin during the late dry season (BARCA-A, November 2008) originated predominantly from the Southern Hemisphere, while during the late wet season (BARCA-B, May 2009) low-level airmasses were dominated by northern-hemispheric inflow and mid-tropospheric airmasses were of mixed origin. In BARCA-A we found strong influence of biomass burning emissions on the composition of the atmosphere over much of the Amazon Basin, with CO enhancements up to 300 ppb and CN concentrations approaching 10 000 cm(-3); the highest values were in the southern part of the Basin at altitudes of 1-3 km. The Delta CN/Delta CO ratios were diagnostic for biomass burning emissions, and were lower in aged than in fresh smoke. Fresh emissions indicated CO/CO2 and CN/CO emission ratios in good agreement with previous work, but our results also highlight the need to consider the residual smoldering combustion that takes place after the active flaming phase of deforestation fires. During the late wet season, in contrast, there was little evidence for a significant presence of biomass smoke. Low CN concentrations (300-500 cm(-3)) prevailed basinwide, and CO mixing ratios were enhanced by only similar to 10 ppb above the mixing line between Northern and Southern Hemisphere air. There was no detectable trend in CO with distance from the coast, but there was a small enhancement of CO in the boundary layer suggesting diffuse biogenic sources from photochemical degradation of biogenic volatile organic compounds or direct biological emission. Simulations of CO distributions during BARCA-A using a range of models yielded general agreement in spatial distribution and confirm the important contribution from biomass burning emissions, but the models evidence some systematic quantitative differences compared to observed CO concentrations. These mismatches appear to be related to problems with the accuracy of the global background fields, the role of vertical transport and biomass smoke injection height, the choice of model resolution, and reliability and temporal resolution of the emissions data base.

Laboratory study on the optical properties of absorbing atmospheric aerosols and field applications

The interaction between aerosols and sun light plays an important role in the radiative balance of Earth’s atmosphere. This interaction is obtained by measuring the removal (extinction), redistribution (scattering), and transformation into heat (absorption) of light by the aerosols; i.e. their optical properties. Knowledge of these properties is crucial for our understanding of the atmospheric system. rn Light absorption by aerosols is a major contributor to the direct and indirect effects on our climate system, and an accurate and sensitive measurement method is crucial to further our understanding. A homebuilt photoacoustic sensor (PAS), measuring at a 532nm wavelength, was fully characterized and its functionality validated for measurements of absorbing aerosols. The optical absorption cross-sections of absorbing polystyrene latex spheres, to be used as a standard for aerosol absorption measurements, were measured and compared to literature values. Additionally, a calibration method using absorbing aerosol of known complex refractive index was presented.rn A new approach to retrieve the effective broadband refractive indices (mbroad,eff) of aerosol particles by a white light aerosol spectrometer (WELAS) optical particle counter (OPC) was achieved. Using a tandem differential mobility analyzer (DMA)-OPC system, the nbroad,eff are obtained for both laboratory and field applications. This method was tested in the laboratory using substances with a wide range of optical properties and it was used in ambient measurements to retrieve the nbroad,eff of biomass burning aerosols in a nationwide burning event in Israel. The retrieved effective broadband refractive indices for laboratory generated scattering aerosols were: ammonium sulfate (AS), glutaric acid (GA), and sodium chloride, all within 4% of literature values. For absorbing substances, nigrosine and various mixtures of nigrosine with AS and GA were measured, as well as a lightly absorbing substance, Suwannee river fulvic acid (SRFA). For the ambient measurements, the calibration curves generated from this method were to follow the optical evolution of biomass burning (BB) aerosols. A decrease in the overall aerosol absorption and scattering for aged aerosols during the day after the fires compared to the smoldering phase of the fires was found. rn The connection between light extinction of aerosols, their chemical composition and hygroscopicity for particles with different degrees of absorption was studied. The extinction cross-section (σext) at 532nm for different mobility diameters was measured at 80% and 90% relative humidity (RH), and at an RH<10%. The ratio of the humidified aerosols to the dry ones, fRHext(%RH,Dry), is presented. For purely scattering aerosols, fRHext(%RH,Dry) is inversely proportional with size; this dependence was suppressed for lightly absorbing ones. In addition, the validity of the mixing rules for water soluble absorbing aerosols is explored. The difference between the derived and calculated real parts of the complex RIs were less than 5.3% for all substances, wavelengths, and RHs. The obtained imaginary parts for the retrieved and calculated RIs were in good agreement with each other, and well within the measurement errors of retrieval from pulsed CRD spectroscopy measurements. Finally, a core-shell structure model is also used to explore the differences between the models, for substances with low growth factors, under these hydration conditions. It was found that at 80% RH and for size parameters less than 2.5, there is less than a 5 % difference between the extinction efficiencies calculated with both models. This difference is within measurement errors; hence, there is no significant difference between the models in this case. However, for greater size parameters the difference can be up to 10%. For 90% RH the differences below a size parameter of 2.5 were up to 7%.rn Finally, the fully characterized PAS together with a cavity ring down spectrometer (CRD), were used to study the optical properties of soot and secondary organic aerosol (SOA) during the SOOT-11 project in the AIDA chamber in Karlsruhe, Germany. The fresh fractal-like soot particles were allowed to coagulate for 28 hours before stepwise coating them with SOA. The single scattering albedo for fresh fractal-like soot was measured to be 0.2 (±0.03), and after allowing the soot to coagulate for 28 hours and coating it with SOA, it increased to 0.71(±0.01). An absorption enhancement of the coated soot of up to 1.71 (±0.03) times from the non-coated coagulated soot was directly measured with the PAS. Monodisperse measurements of SOA and soot coated with SOA were performed to derive the complex refractive index (m) of both aerosols. A complex refractive index of m = 1.471(±0.008) + i0.0(±0.002) for the SOA-αO3 was retrieved. For the compact coagulated soot a preliminary complex refractive index of m = 2.04(+0.21/-0.14) + i0.34(+0.18/-0.06) with 10nm(+4/-6) coating thickness was retrieved.rn These detail properties can be use by modelers to decrease uncertainties in assessing climatic impacts of the different species and to improve weather forecasting.rn

LIBERTAÇÃO NAS TRILHAS DA JUSTIÇA: Estudo histórico e hermenêutico de Isaías 42,1-4

O presente trabalho tem como objetivo propor um estudo do cântico do escravo de Javé em Isaías 42,1- 4. Javé apresenta uma nova liderança, com um novo jeito de pensar e de agir para reconstruir um mundo novo baseado no direito e na solidariedade. É uma tarefa desafiadora para mim e ao mesmo tempo uma alegria em poder compartilhar com os meus amigos o conteúdo de um texto do Antigo Testamento. Afinal, o cântico do escravo de Javé é uma fonte inesgotável de sabedoria. Saciou o povo judaíta exilado a de dois mil e quinhentos anos atrás e continua jorrando água viva até em nossos dias matando a sede de todos aqueles e aquelas que lutam pela justiça. Os versos escolhidos são frutos de uma experiência de vida concreta dos exilados desacreditados por todos no cativeiro da Babilônia. No fundo é uma crítica aos falsos deuses criados pelos poderosos para justificar um sistema de opressão. A criatividade do profeta está em retomar os eventos históricos que marcaram a vida do povo exilado e atualizá-los dentro de um novo contexto histórico. Isto demonstra sua agilidade no conhecimento. Cada palavra é pensada dentro de um contexto maior envolvendo a vida e a história. O profeta é um sábio poeta, que fala de Deus como ninguém falou antes. Utiliza símbolos, imagens e metáforas que apontam para um mundo novo que ainda não existe, onde reinará o direito, a justiça e a paz. Essa mudança acontecerá a partir da missão que a liderança eleita desempenhará junto do povo oprimido e injustiçado. O líder será como o fermento na massa para a nova sociedade, baseada na igualdade e na partilha. O espírito de Javé estará agindo sobre ele para que ele não desanime da missão e que ela possa alcançar o seu objetivo. Essa nova liderança eleita por Javé agirá discretamente em silêncio entre os pobres e enfraquecidos. A missão beneficiará primeiramente às nações. Aqueles e aquelas que vivem em terras estrangeiras como migrantes. Depois contemplará de modo especial os pobres que estão correndo risco de vida, cana rachada e pavio vacilante e por fim a missão atingirá todos os povos da terra. Essa perspectiva traduz a vontade de Deus que é a salvação de toda a humanidade.(AU)

LIBERTAÇÃO NAS TRILHAS DA JUSTIÇA: Estudo histórico e hermenêutico de Isaías 42,1-4

O presente trabalho tem como objetivo propor um estudo do cântico do escravo de Javé em Isaías 42,1- 4. Javé apresenta uma nova liderança, com um novo jeito de pensar e de agir para reconstruir um mundo novo baseado no direito e na solidariedade. É uma tarefa desafiadora para mim e ao mesmo tempo uma alegria em poder compartilhar com os meus amigos o conteúdo de um texto do Antigo Testamento. Afinal, o cântico do escravo de Javé é uma fonte inesgotável de sabedoria. Saciou o povo judaíta exilado a de dois mil e quinhentos anos atrás e continua jorrando água viva até em nossos dias matando a sede de todos aqueles e aquelas que lutam pela justiça. Os versos escolhidos são frutos de uma experiência de vida concreta dos exilados desacreditados por todos no cativeiro da Babilônia. No fundo é uma crítica aos falsos deuses criados pelos poderosos para justificar um sistema de opressão. A criatividade do profeta está em retomar os eventos históricos que marcaram a vida do povo exilado e atualizá-los dentro de um novo contexto histórico. Isto demonstra sua agilidade no conhecimento. Cada palavra é pensada dentro de um contexto maior envolvendo a vida e a história. O profeta é um sábio poeta, que fala de Deus como ninguém falou antes. Utiliza símbolos, imagens e metáforas que apontam para um mundo novo que ainda não existe, onde reinará o direito, a justiça e a paz. Essa mudança acontecerá a partir da missão que a liderança eleita desempenhará junto do povo oprimido e injustiçado. O líder será como o fermento na massa para a nova sociedade, baseada na igualdade e na partilha. O espírito de Javé estará agindo sobre ele para que ele não desanime da missão e que ela possa alcançar o seu objetivo. Essa nova liderança eleita por Javé agirá discretamente em silêncio entre os pobres e enfraquecidos. A missão beneficiará primeiramente às nações. Aqueles e aquelas que vivem em terras estrangeiras como migrantes. Depois contemplará de modo especial os pobres que estão correndo risco de vida, cana rachada e pavio vacilante e por fim a missão atingirá todos os povos da terra. Essa perspectiva traduz a vontade de Deus que é a salvação de toda a humanidade.(AU)