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

Amorim, E. B.; Carvalho, J. A.; Soares Neto, T. G.; Anselmo, E.; Saito, V. O.; Dias, F. F.; Santos, J. C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 52-59
Português
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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.

‣ Estudo experimental da combustão molhada na recuperação de oleo pesado; Experimental study of the wet combustion on heavy oil recovery

Lucia Ines Bonet Gonçalves
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/02/2010 Português
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Uma das formas de se melhorar o desempenho do processo de recuperação de petróleo conhecido como combustão in situ direta seca, é injetar água simultaneamente ou alternadamente com o ar, o que se denomina de combustão in situ direta molhada. O calor específico do ar seco é consideravelmente menor do que o da água, de tal forma que esta pode realizar um melhor transporte do calor gerado pela frente de combustão, promovendo uma redução na quantidade de ar requerido para varrer um determinado volume do reservatório. O presente trabalho tem como objetivos avaliar, através de ensaios em tubo de combustão, o desempenho da combustão molhada para um óleo pesado (12,88°API) procedente da Bacia do Espírito Santo e obter parâmetros que possam ajudar no balizamento de um futuro projeto piloto. Para isto, foram realizados quatro ensaios em tubo de combustão (um de combustão seca e três de combustão molhada), utilizando o aparato experimental do Laboratório de Métodos Térmicos de Recuperação do Departamento de Engenharia de Petróleo da UNICAMP e também foi elaborado um modelo térmico de simulação para auxiliar na predição dos testes em laboratório, utilizando um simulador comercial. Os resultados experimentais mostram que o processo de combustão molhada apresenta-se estável para o óleo em estudo na medida em que as condições experimentais mantêm-se controladas. Para as razões água-ar estudadas (1...

‣ Conditional moment closure modeling of turbulent nonpremixed combustion in diluted hot coflow

Kim, S.; Huh, K.; Dally, B.
Fonte: The Combustion Institute Publicador: The Combustion Institute
Tipo: Artigo de Revista Científica
Publicado em //2005 Português
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The conditional moment closure (CMC) model is applied to predict flame structures and NO formation in the moderate and intense low oxygen dilution combustion mode. The effects of oxygen concentration in a hot diluted oxidant stream are investigated in the experimental condition of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154]. The GRI 2.11 Mech is used for description of chemical reaction including NOx chemistry. The conditional scalar dissipation rate, which describes the effect of turbulent mixing on finite chemistry, is calculated by integrating the transport equation for probability density function (PDF). A new PDF is proposed to describe three stream mixing in terms of a single mixture fraction. The conditional mean predictions of temperature, and CO, OH, and NO mass fractions are in good agreement with measurements. The unconditional Favre mean predictions of CO and NO mass fractions are also in reasonable agreement. Upstream underprediction of OH and NO in the low oxygen concentration case may be attributed to uncertainty in low temperature reaction mechanism and mixing prediction. Differential diffusion effects are shown to be nonnegligible in the present flames. The CMC model is an attractive choice for simulation of MILD combustion in which conditional fluctuations of reactive scalars are small enough for first-order closure of conditional mean reaction rates to remain valid.; http://www.elsevier.com/wps/find/journaldescription.cws_home/703522/description#description; Seung Hyun Kim...

‣ Laser diagnostics in MILD combustion.

Medwell, Paul Ross
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado Formato: 365088 bytes; 3056952 bytes; 2099352 bytes; 336211 bytes; application/pdf; application/pdf; application/pdf; application/pdf
Publicado em //2007 Português
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Despite mounting concerns of looming global warming and fuel shortages, combustion will remain the predominant source of fulfilling the world’s ever-increasing demand for energy in the foreseeable future. In light of these issues, the combustion regime known as Moderate and Intense Low oxygen Dilution (MILD) combustion has the potential of offering increased efficiency whilst lowering pollutant emissions. Essentially, MILD combustion relies on the reuse of the exhaust gases from the combustion process to simultaneously dilute the oxygen concentration of the oxidant stream, and increase its temperature. The benefit of this technique is that it results in a vast reduction in emissions, especially oxides of nitrogen. In addition, the thermal efficiency of the combustion process is increased, reducing fuel demands, as well as producing a more uniform heating profile and subsequently better product quality for many applications. The recirculation of exhaust gas and heat has been utilised for applications in the past. MILD combustion aims to extend the advantages of heat recovery and exhaust gas recirculation beyond the boundaries that are otherwise possible using conventional techniques. The relatively new concept of MILD combustion is a major advancement to the previous technology...

‣ Progress and recent trend in MILD combustion

Li, P.; Mi, J.; Dally, B.; Wang, F.; Wang, L.; Liu, Z.; Chen, S.; Zheng, C.
Fonte: Zhongguo Kexue Zazhishe Publicador: Zhongguo Kexue Zazhishe
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
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Moderate or intense low oxygen dilution (MILD) combustion plays a significant role in the mitigation of combustion-generated pollutants and greenhouse gases whilst meeting thermal efficiency needs. However, due to the lack of the fundamental knowledge on this combustion, there is a misconception that MILD combustion should be established by high preheating of the air, which has limited its application. Our research and development on this combustion has been performed for several years. We have found that the requirements for establishing the MILD combustion are more relaxed than previously. It is also revealed that this combustion of different type, i.e., non-premixed, partially premixed and fully premixed, can be achieved by firing various fuels (i.e., gaseous, liquid and solid fuels). It is suggested that the application of the MILD combustion can be expanded significantly. The present review summarizes the progress and recent trend made in the R&D of this combustion and recommends further fundamental studies for improving our knowledge and widening its applications.; PengFei Li, JianChun Mi, B. B. Dally, FeiFei Wang, Lin Wang, ZhaoHui Liu, Sheng Chen and ChuGuang Zheng

‣ Combustion of pre-dried brown coal in a utility furnace using recycled flue gas

Tian, Z.; Witt, P.; Schwarz, M.; Yang, W.
Fonte: The Combustion Institute; Australia Publicador: The Combustion Institute; Australia
Tipo: Conference paper
Publicado em //2011 Português
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This report describes a numerical study of pre-dried coal combustion in unit No. 3 furnace at TRUenergy’s Yallourn power plant. This utility unit is designed for raw brown coal without any pre-drying process. A validated computational fluid dynamics (CFD) model is used to investigate the combustion of the pre-dried coal with recycled flue gas that is added to the fuel gas. The temperature distributions, wall heat fluxes and heat supply to boiler for the recycled flue gas cases are similar to that of the raw coal combustion case under current operating conditions. Therefore, use of recirculated flue gas is proposed as the preferred option for future operation of the furnace with pre-dried coal. Nevertheless, further studies are essential to understand the technical and financial feasibility of using flue gas to maintain the fuel gas flow rate.; https://publications.csiro.au/rpr/pub?list=BRO&pid=csiro:EP115824&sb=RECENT&n=2&rpp=10&page=1&tr=14&dc4.creator=yang%2C%20william&dr=all; Zhao Feng Tian, Peter Witt, Phil Schwarz and Willian Yang

‣ Application of chemical looping combustion for solar thermal energy storage

Jafarian, S.; Arjomandi, M.; Nathan, G.; Nasehi, S.
Fonte: The Combustion Institute; Australia Publicador: The Combustion Institute; Australia
Tipo: Conference paper
Publicado em //2011 Português
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In this paper a solar hybrid chemical looping combustion (CLC) system for solar thermal energy storage (TES) is proposed. For those combinations of fuels and metal oxides in CLC systems with an endothermic reaction, there is a potential to utilize solar thermal energy to drive the CLC reactions and so to allow the solar thermal energy to be stored as a reduced metal oxide. The application of oxygen carrier particles for solar thermal energy storage is also possible. A novel solar hybrid system is proposed and assessed, in generation cycles to enable base load generation from solar thermal energy. For this purpose three reservoirs are added to a CLC system to store the oxygen carrier particles and a cavity solar reactor is used as the fuel reactor. The ASPEN PLUS software is used to simulate the hybrid process. Basic validation of the model is performed using independent simulation result reported previously and the model is then used to calculate operating temperature, solar efficiency and solar fraction of the system. The results identify potential benefits from the solar hybridization of a CLC system.; S.M. Jafarian, M. Arjomandi, G. Nathan and S.M. Nasehi

‣ Experimental investigation of high frequency combustion instability in cryogenic oxygen-hydrogen rocket engines.

Hardi, Justin S.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2012 Português
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Self-sustaining pressure oscillations in the combustion chamber, or combustion instability, is a commonly encountered and potentially damaging phenomenon in liquid propellant rocket engines (LPREs). In the high-frequency variety of combustion instability, the pressure oscillations in the combustion chamber take on the form and frequency of an acoustic resonance mode of the combustion chamber volume. The most common mode in naturally occurring instability, and also the most destructive, is the first tangential mode, with acoustic gas oscillations oriented transversally to the direction of propellant injection. The instability is driven by the coupling between acoustic oscillations and unsteady energy release from combustion. The mechanisms through which injection and combustion firstly respond to the acoustic field, and secondly feed energy back into the acoustic field have not yet been fully characterised. Shear coaxial-type injectors are common in LPREs. Past experimental and numerical research efforts have investigated the interaction between this type of injector and transverse acoustic fields. Some experimental efforts have successfully forced transverse acoustic modes and studied their influence on shear coaxial injection under LPRE-like conditions. Acoustic forcing of coaxially injected LOx/H₂ has previously been conducted only at low pressures and injection performance levels. This work addresses the lack of experimental data available for the interaction of shear coaxial injection of LOx/H₂ with acoustics under conditions representative of industrial engines. A new experimental rocket combustor...

‣ Reaction pathways to soot formation in petrodiesel and biodiesel combustion

Cai, G.; Abraham, J.
Fonte: The Combustion Institue; Online Publicador: The Combustion Institue; Online
Tipo: Conference paper
Publicado em //2013 Português
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In this study, simulations are employed to improve the fundamental understanding of soot formation from a chemical kinetics perspective during biodiesel and petrodiesel combustion under pressure and temperature conditions in engines. n-Heptane is used as the surrogate for petrodiesel and a ternary mixture of methyl decanoate, methyl-9-decenoate, and n-heptane as the surrogate for biodiesel. In the case of the ternary biodiesel surrogate, a 211-species reduced mechanism is employed to model the chemical kinetics. This mechanism was derived as part of this work by combining reactions from the 160-species n-heptane mechanism with reactions from a skeletal 115-species mechanism proposed in the literature. Soot kinetics is represented using a chemical mechanism that models the growth of soot precursors starting from a single aromatic ring by hydrogen abstraction and carbon (acetylene) addition. The influence of turbulence is indirectly modelled through an imposed strain rate in the simulations. The computations are carried out using a strained laminar flamelet code (SLFC). Analysis of the results shows that the significant reduction in soot observed in biodiesel combustion results from an increase in the concentration of alkoxy species during the fuel breakdown process which...

‣ A study of combustion characteristics of pulverised coal under MILD combustion conditions

Saha, M.; Dally, B.; Medwell, P.; Cleary, E.
Fonte: The Combustion Institue; Online Publicador: The Combustion Institue; Online
Tipo: Conference paper
Publicado em //2013 Português
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In this experimental work, a laboratory-scale recuperative furnace has been used to investigate the sustainability of Moderate or Intense Low Oxygen Dilution (MILD) combustion with pulverised coal. Low-rank and high volatile Kingston brown coal and high-rank and low volatile Bowen Basin black coal with particle size in the range of 38-180 μm were injected into the furnace using either CO2 or N2 as a carrier gas. Operating conditions for stable MILD combustion of pulverised coal have been identified and evidencing MILD condition is achievable without any additional pre-heating of the air. The O2 and CO emissions were measured in parallel with NO emission. A water cooled sampling probe was used to conduct in-furnace gas sampling. Measurements of in-furnace gas concentration of CO and NO and in-furnace temperatures are presented. It was found that a significant reduction of NO emission owing to the strong NO reburning reaction inside the furnace. These findings, together with the potentiality of MILD conditions for soot depression and destruction, open the possibility of using high rank black and low rank brown coal with this technology.; http://cfe.uwa.edu.au/news/acs2013; http://www.anz-combustioninstitute.org/; M. Saha, B. B. Dally...

‣ The influence of coal particle and air jet momenta on MILD combustion in a recuperative furnace

Cleary, E.; Medwell, P.; Dally, B.
Fonte: The Combustion Institue; Online Publicador: The Combustion Institue; Online
Tipo: Conference paper
Publicado em //2013 Português
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The moderate or intense low-oxygen dilution (MILD) combustion regime is a promising technology that operates at high combustion efficiency and lessens pollutant emissions. This numerical study of a parallel jet recuperative MILD combustion furnace investigates the effects of coal particle size and inlet air momentum on furnace dynamics and global CO emissions. It is found that coal particle size affects the coal penetration depth within the furnace and the location of a particle stagnation point. The effects of air inlet momentum are tested in two ways, first by raising the inlet temperature at constant mass flow rate, and second by increasing the mass flow rate at constant temperature. In both cases, increasing the air jet momentum broadens the reaction zone and facilitates MILD combustion, but also increases CO emissions due to lowered reaction rates.; http://cfe.uwa.edu.au/news/acs2013; http://www.anz-combustioninstitute.org/; Emmet M. Cleary, Paul R. Medwell, Bassam B. Dally

‣ Modelo pseudocinético para a simulação numérica da combustão in-situ na escala da campo; Pseudokinetic model for field-scale simulation of in-situ combustion

Diana Patricia Mercado Sierra
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 24/02/2015 Português
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A combustão in-situ é um processo multiescala, multifísico que envolve simultaneamente o escoamento de fluidos no meio poroso, o equilíbrio de fases e a cinética das reações químicas. A simulação desse processo tem alcançado um elevado grau de desenvolvimento, no entanto, mecanismos básicos ainda são representados de maneira incompleta, impondo inúmeros desafios na modelagem. A dificuldade de modelar fenômenos relacionados com a combustão tem a ver com a representação do efeito da frente de combustão e a modelagem do consumo de combustível. Na combustão in-situ as reações químicas acontecem em uma zona delgada de menos de um metro de espessura, que é pequena quando comparada com a escala do reservatório de centenas ou milhares de metros. Na simulação na escala de campo, o uso de células de tamanho maior do que a zona de reação leva a erros na distribuição da temperatura. Consequentemente, a velocidade das reações não pode ser bem representada. De outro lado, os simuladores não permitem controlar a ocorrência das reações a partir da energia de ativação. Como resultado, o início das reações se torna independente da temperatura. O objetivo desta tese é desenvolver um modelo pseudocinético para a simulação numérica da combustão in-situ na escala de campo. Com o modelo pseudocinético pretende-se representar os fenômenos na zona de combustão...

‣ Formation of Mo−Si−Ti Alloys by Self−propagating Combustion Synthesis

Wu,Jie; Zhu,Gaoming; Feng,Peizhong; Zhou,Xianguo; Wang,Xiaohong; Akhtar,Farid
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2015 Português
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Test specimens with nominal compositions MoSi2, (Mo0.9Ti0.1)Si2, (Mo0.8Ti0.2)Si2, (Mo0.7Ti0.3)Si2, (Mo0.6Ti0.4)Si2, (Mo0.5Ti0.5)Si2 and (Mo0.4Ti0.6)Si2 were prepared by combustion synthesis. The combustion mode, propagation velocity of combustion wave, combustion temperature and product structure were investigated. Specimens MoSi2, (Mo0.9Ti0.1)Si2, (Mo0.8Ti0.2)Si2, (Mo0.7Ti0.3)Si2, underwent spontaneously self−propagating combustion synthesis. However, the (Mo0.6Ti0.4)Si2 and (Mo0.5Ti0.5)Si2 specimens required a sustainable energy supply to complete the combustion synthesis reaction. There was no combustion synthesis reaction in specimen (Mo0.4Ti0.6)Si2. The combustion wave propagated along a spiral trajectory from top to the bottom of the specimen compacts in a layer by layer mode. The propagation velocity of the combustion wave reduced with the addition of titanium. The X-ray diffraction analysis showed that the Cllb-MoSi2 and C40-(Mo,Ti)Si2type phases were formed during combustion synthesis. The intensity of diffraction peaks of C40-(Mo,Ti)Si2 phase increased with Ti content.

‣ Modèles de flammelette en combustion turbulente avec extinction et réallumage : étude asymptotique et numérique, estimation d’erreur a posteriori et modélisation adaptative

Turbis, Pascal
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
Português
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On s’intéresse ici aux erreurs de modélisation liées à l’usage de modèles de flammelette sous-maille en combustion turbulente non prémélangée. Le but de cette thèse est de développer une stratégie d’estimation d’erreur a posteriori pour déterminer le meilleur modèle parmi une hiérarchie, à un coût numérique similaire à l’utilisation de ces mêmes modèles. Dans un premier temps, une stratégie faisant appel à un estimateur basé sur les résidus pondérés est développée et testée sur un système d’équations d’advection-diffusion-réaction. Dans un deuxième temps, on teste la méthodologie d’estimation d’erreur sur un autre système d’équations, où des effets d’extinction et de réallumage sont ajoutés. Lorsqu’il n’y a pas d’advection, une analyse asymptotique rigoureuse montre l’existence de plusieurs régimes de combustion déjà observés dans les simulations numériques. Nous obtenons une approximation des paramètres de réallumage et d’extinction avec la courbe en «S», un graphe de la température maximale de la flamme en fonction du nombre de Damköhler, composée de trois branches et d’une double courbure. En ajoutant des effets advectifs, on obtient également une courbe en «S» correspondant aux régimes de combustion déjà identifiés. Nous comparons les erreurs de modélisation liées aux approximations asymptotiques dans les deux régimes stables et établissons une nouvelle hiérarchie des modèles en fonction du régime de combustion. Ces erreurs sont comparées aux estimations données par la stratégie d’estimation d’erreur. Si un seul régime stable de combustion existe...

‣ Combustion of waste oils simulating their injection in blast furnace tuyeres.; Combustión de aceites residuales simulando su inyeccion en las toberas del horno alto.

Cores Sánchez, A.; Ferreira-Barragáns, Silvia; Isidro, A.; Muñiz, M.
Fonte: Consejo Superior de Investigaciones Científicas (España) Publicador: Consejo Superior de Investigaciones Científicas (España)
Tipo: Artículo Formato: 3012700 bytes; application/pdf
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14 pages, 6 figures, 11 tables and 2 appendixes.; [EN]A study has been made of the combustion of different waste oils produced in an iron and steel works. Combustion is achieved by injecting the waste oil at flows of 10-20 kg/h in a combustion chamber that simulates the conditions of the blast furnace tuyere zone. The waste oil is preheated to 65-90 °C in order to achieve conditions of fluidity and is injected by spraying into the combustion chamber. During combustion the temperatures and the CO2, O2, CO N2 and H2 contents of the gases in the combustion chamber are constantly recorded. The efficiency of the combustion of each waste oil is determined.; [ES] Se realiza un estudio de la combustión de diferentes aceites residuales que se producen en las plantas siderúrgicas. La combustión se consigue al inyectar el aceite residual, con caudales de 10-20 kg/h, en una cámara de combustión que simula las condiciones del horno alto en la zona de toberas. El aceite residual se precalienta a 65-90 °C para conseguir las condiciones de fluidez y se inyecta en la cámara de combustión. Durante la combustión, se registran de modo continuo las temperaturas y los contenidos de CO2, O2, CO, N2 y H2 en los gases de la cámara de combustión. Se calcula la eficiencia de la combustión de cada aceite residual.; Peer reviewed

‣ Posibilidades del análisis de imagen para el estudio de la sintesis de materiales por combustión; Study of material combustion synthesis by image analysis

Chinarro Martín, Eva; Moreno Burriel, Berta; Jurado Egea, José Ramón; Martín Andrés, Diego; González, L.; Villanueva Martínez, Eugenio; Guinea Díaz, Domingo
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 337931 bytes; application/pdf
Português
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[ES] El análisis de la imagen obtenida por una cámara de video digital se utiliza para el estudio de la reacción de síntesis por combustión de Sm0.95CoO3-δ. El método de combustión presenta como característica intrínseca la generación de materiales nanométricos cerámicos y metal-cerámicos; permitiendo la producción de compuestos con actividad catalítica. En este trabajo se obtienen polvos de tamaño de cristalito entorno a 5 nm, con una superficie específica de 24 m2/g y como consecuencia bastante reactivos. Se llevaron cabo estudios preliminares sobre la etapa de ignición de la síntesis usando el análisis de imagen por descomposición de los planos de los tres colores primarios; dichos experimentos muestran que la llama generada en esta etapa de ignición es un proceso termodinámicamente aleatorio. La finalidad de este trabajo es establecer un protocolo de experimentación para la futura correlación entre los parámetros de la síntesis por combustión de un material, naturaleza y concentración de precursores entre otros, y la distribución de temperatura durante la ignición, con objeto de optimizar y controlar el proceso. Se abre una línea de investigación basada en la utilización de la técnica de análisis de imagen para realizar un seguimiento controlado de la evolución de la temperatura e intensidad de la llama durante la etapa de ignición de la síntesis por combustión de un material.; [EN] Analysis of the recorded image by a digital video camera of the Sm0.95CoO3-δ combustion synthesis is carried out. Intrinsically the combustion method yields nanometric materials (ceramic and metal-ceramic); allowing to produce catalytic powders. In this work...

‣ Physical aspects and modelling of turbulent MILD combustion

Minamoto, Yuki
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
Português
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Moderate or Intense Low-oxygen Dilution (MILD) combustion is one of combustion technologies which can improve efficiency and reduce emissions simultaneously. This combustion type is characterised by the highly preheated reactant temperature and the relatively small temperature rise during combustion due to the intense dilution of the reactant mixture. These unique combustion conditions give MILD combustion very attractive features such as high combustion efficiency, reduction of pollutant emissions, attenuation of combustion instabilities and flexibility of the flow field. However, our understanding of MILD combustion is not enough to employ the MILD combustion technology further for modern combustion devices. In this thesis, Direct Numerical Simulation (DNS) has been carried out for turbulent MILD combustion under four MILD and classical premixed conditions. A two-phase strategy is employed in the DNS to include the effect of imperfect mixing between fresh and exhaust gases before intense chemical reactions start. In the simulated instantaneous MILD reaction rate fields, both thin and distributed reaction zones are observed. Thin reaction zones having flamelet like characteristics propagate until colliding with other thin reaction zones to produce distributed reaction zones. Also...

‣ Reaction zones and their structure in MILD combustion

Minamoto, Y.; Swaminathan, N.; Cant, R. S.; Leung, T.
Fonte: Combustion Science and Technology Volume 186, Issue 8, 2014. DOI: 10.1080/00102202.2014.902814 Publicador: Combustion Science and Technology Volume 186, Issue 8, 2014. DOI: 10.1080/00102202.2014.902814
Tipo: Article; accepted version
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This is an Accepted Manuscript of an article published by Taylor & Francis in Combustion Science and Technology on 26 Jun 2014, available online: http://wwww.tandfonline.com/10.1080/00102202.2014.902814.; Three-dimensional direct numerical simulation (DNS) of turbulent combustion under moderate and intense low-oxygen dilution (MILD) conditions has been carried out inside a cuboid with inflow and outflow boundaries on the upstream and downstreamfaces respectively. The initial and inflowing mixture and turbulence fields are constructed carefully to be representative of MILD conditions involving partially mixed pockets of unburnt and burnt gases. The combustion kinetics is modelled using a skeletal mechanism for methane-air combustion, including non-unity Lewis numbers for species and temperature dependent transport properties. The DNS data is analysed to study theMILD reaction zone structure and its behaviour. The results show that the instantaneous reaction zones are convoluted and the degree of convolution increases with dilution and turbulence levels. Interactions of reaction zones occur frequently and are spread out in a large portion of the computational domain due to the mixture non-uniformity and high turbulence level. These interactions lead to local thickening of reaction zones yielding an appearance of distributed combustion despite the presence of local thin reaction zones. A canonical MILD flame element...

‣ Scalar gradient behaviour in MILD combustion

Minamoto, Y.; Swaminathan, N.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
Português
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This is the accepted manuscript. The final published version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0010218013003799.; The results of three-dimensional Direct Numerical Simulation (DNS) of Moderate, Intense Low-oxygen Dilution (MILD) and conventional premixed turbulent combustion conducted using a skeletal mechanism including the effects of nonunity Lewis numbers and temperature dependent transport properties are analysed to investigate combustion characteristics using scalar gradient information. The DNS data is also used to synthesise laser induced fluorescence (LIF) signals of OH, CH2O, and CHO. These signals are analysed to verify if they can be used to study turbulent MILD combustion and it has been observed that at least two (OH and CH2O) LIF signals are required since the OH increase across the reaction zone is smaller inMILD combustion compared to premixed combustion. The scalar gradient PDFs conditioned on the reaction rate obtained from the DNS data and synthesised LIF signals suggests a strong gradient in the direction normal to the MILD reaction zone with moderate reaction rate implying flamelet combustion. However, the PDF of the normal gradient is as broad as for the tangential gradient when the reaction rate is high. This suggests a non-flamelet behaviour...

‣ Effects of gas-solid nonequilibrium in filtration combustion

Wahle, Christopher; Matkowsky, Bernard; Aldushin, Anatoly
Fonte: Taylor and Francis Ltd Publicador: Taylor and Francis Ltd
Tipo: Artigo de Revista Científica
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To determine the effects of gas-solid nonequilibrium on forced filtration combustion (FC) waves, a two-temperature model is employed, with separate temperature fields for the solid and gas particles. We consider heterogeneous (solid/gas) combustion in a porous sample with a prescribed gas flux at the inlet. If the reaction is initiated at the inlet (outlet) of the sample and the combustion wave travels in the direction of (opposite to ) gas filtration it is referred to as coflow (counterflow) FC. We determine the effects of gas-solid nonequilibrium on various aspects of forced FC waves. First, we consider coflow FC waves, in which case the gas infiltrating through the hot product region significantly enhances the propagation of the combustion wave. For a relatively small gas flux, the infiltrating gas delivers heat from hot product to the combustion layer, thus increasing the combustion temperature and, hence, the combustion rate. Propagation of such waves is controlled by conduction of the heat released in the reaction to the preheat zone. Conductively driven coflow FC waves have been studied extensively using one-temperature models, which assume a very large rate of interphase heat exchange between the solid and the gas, so that thermal equilibrium is attained almost immediately. However...