Propagación de llamas premezcladas

El estudio del fenómeno de la combustión es de gran relevancia científica y tecnológica para la sociedad. La crisis climática que enfrenta la sociedad ha llevado a los científicos a proponer diferentes estrategias para mitigar el impacto en el medio ambiente. Una de las estrategias propuestas es ampliar el uso de combustibles alternativos y de biocombustibles, aprovechando sus características menos contaminantes. Algunos combustibles alternativos, que son considerados como opciones promisoras, son el gas de síntesis, biogas, etanol, hidrogeno y farnesano, entre otros. Sin embargo, el desarrollo de tecnologías que permitan tal uso depende del conocimiento fundamental de los procesos de combustión (Law, 2006). Históricamente, el uso de los combustibles tradicionales ha promovido el desarrollo teórico y experimental de la ciencia de la combustión, con investigaciones que datan de finales del siglo XIX hasta la actualidad. El estudio de la combustión implica el acoplamiento de reacciones químicas (Sarathy et al., 2014) con procesos de transferencia de calor en fluidos compresibles. Además, en el caso de las detonaciones (Ciccarelli & Dorofeev, 2008), y en muchas aplicaciones prácticas, la combustión es turbulenta, adicionando otros aspectos interesantes a su estudio (Swaminathan & Bray, 2011). En términos generales, la combustión se divide en el estudio de llamas premezcladas y no-premezcladas. En esta conferencia abordaré algunos fenómenos relevantes para el estudio de las llamas premezcladas, como son la velocidad de llama laminar, los límites de inflamabilidad, las deflagraciones y las detonaciones

CO2 emission factors and carbon losses for off-road mining trucks

There are myriad questions that remain to be answered in greenhouse gas (GHG) emissions trading. This article addresses carbon dioxide (CO2 ) emission factors and carbon losses from heavy equipment that is used to transport ores. Differences occurred between the Intergovernmental Panel for Climate Change (IPCC) emission factor and those that were obtained by considering incomplete combustion and on-site exhaust concentration measurements. Emissions from four off-road vehicles were analyzed. They operated at idle (loading, unloading, and queuing) and in motion (front and rear, loaded and unloaded). The results show that the average CO2 emission factors can be as low as 64.8% of the IPCC standard value for diesel fuel. On the other hand, carbon losses can be up to 33.5% and energy losses up to 25.5%. To the best of the authors’ knowledge, the method that was developed here is innovative, simple, useful, and easily applicable in determining CO2 emission factors and fuel losses for heavy machinery

Experimental assessment and modeling of solar air heater with V shape roughness on absorber plate

A roughness of the absorber plate can improve the efficiency of a solar air heater. To boost the efficiency of triangle solar air heaters, this research presents the results of a comparison study between with and without rib roughness on absorber plates. Both use black paint with graphene nanoparticles infused into it, coating an absorber plate. Both numerical and experimental methods have been used to examine the impact of surface roughness on friction factors and heat transport properties. ANSYS 14.5 software module and RNG turbulence, k-€ model is used to conduct a three-dimensional simulation and solve the governing equations in the turbulent situation. Based on experimental data, it has been established that smooth plates are more efficient in converting heat into useful work than rough ones, on average, by a factor of 4.82 and 4.46, respectively. The length of the duct in the solar air heater mitigates the temperature gradient seen in the simulation result. The roughness of V-shaped ribs has a far larger effect on the heat transfer and friction factor properties than do variations in relative roughness pitch (P/e) and Reynolds number (Re). Experimental observations supported by modeling and simulation confirms that triangular duct absorber surface roughness provides improved outcome

Evaluación de la gasificación de biomasa en gasificadores downdraft aplicando la condición de equilibrio termodinámico

TesisEl objetivo del presente trabajo es desarrollar modelos de equilibrio estequiométrico que permitan el estudio de los efectos de ciertos parámetros en el proceso de gasificación de un combustible en particular. En total fueron evaluados cuatro modelos con el objetivo de determinar la composición del gas de síntesis. El modelo Mi es puramente de equilibrio, por otro lado el M2 se basa en la modificación de las constantes de equilibrio termodinámico aplicando dos factores de corrección obtenidos utilizando datos experimentales publicados. Otros dos modelos, M3 y M4, se basaron en correlaciones. Mientras el modelo M4 esta basado en correlaciones para determinar el valor de las constantes de equilibrio, el modelo M3 esta basado en correlaciones que determinan la relación de los contenidos de H2, CO y CO en el gas de síntesis. El modelo M2 demostró ser el más exacto y versátil entro los cuatro modelos, y también mostró mejores resultados que algunos modelos publicados previamente. También se presenta un caso de estudio para la gasificación de trozos madera y glicerol en una proporción de 80% y 20% en peso, respectivamente, el caso de estudio consideró razones de equivalencia entre 0.3 y 0.5, contenidos de humedad entre 0% y 20% y porcentajes de oxígeno en el agente de gasificación de i00%, 60% y 21%

Simulação da produção e combustão de gás de síntese oriundo de gaseificadores de leite fixo

O objetivo do presente trabalho é desenvolver e comparar quatro modelos, baseados em conceitos de equilíbrio termoquímico, para predizer a composição do gás de síntese de biomassa obtido de gaseificadores de corrente descendente e de corrente ascendente. Assim, também é objetivo do presente trabalho o desenvolvimento de um modelo para determinar a temperatura e a composição do gás produto da combustão de gás de síntese, à pressão e volume constantes. Um dos modelos desenvolvidos para determinar a composição do gás de síntese (M4) leva em conta o carbono não convertido em estado sólido. Os modelos M2 e M3 foram desenvolvidos considerando diferentes reações de equilíbrio, que envolvem o metano. Como uma tentativa para melhorar a aproximação com dados experimentais, a equação de conservação da energia foi corrigida para os modelos M2, M3 e M4, considerando um método diferente para determinar o valor da entalpia de formação da biomassa. Para o modelo M1, a entalpia de formação da biomassa foi determinada aplicando a definição do PCS. Todos os modelos de equilíbrio para a gaseificação foram testados com dados experimentais de gaseificação de biomassa em gaseificadores de corrente descendente tomados de quatro trabalho diferentes, e com dados de gaseificadores de corrente ascendente de dois trabalhos diferentes. Foram considerados diferentes tipos de biomassa, como madeira, pó de serragem, madeira de seringueira, madeira peletizada e lodo de esgoto peletizadoThe goal of the present work is to develop and compare four models, based on thermochemical equilibrium concepts, to predict the composition of synthesis gas obtained from biomass downdraft and updraft gasifiers. Also was a goal of the present work to develop a model to determine the temperature and composition of the product gas originated from the synthesis gas combustion, at constant pressure and at constant volume. One of the models developed to determine the synthesis gas composition (M4) takes into account unconverted carbon in solid state. Models M2 and M3 were created considering different equilibrium reactions, involving methane. In order to improve model accuracy, the energy balance equation was corrected, for models M2, M3 and M4, by considering a different method to calculate the formation enthalpy of biomass. For model M1 the formation enthalpy of biomass was evaluated applying the definition of HHV. All equilibrium gasification models were tested against experimental data of biomass downdraft gasifiers reported in four different works, and experimental data of biomass updraft gasifiers reported in two different works. Different biomass materials, like wood, sawdust, rubber wood, pelletized softwood and pelletized sewage sludge were consideredCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Modeling of syngas composition obtained from fixed bed gasifiers using Kuhn–Tucker multipliers

This work consists of developing a predictive model (PM) for syngas composition obtained from biomass gasification in fixed bed gasifiers. The PM is composed of three correlations which are made for carbon conversion efficiency, gasification temperature and the correction factor for the equilibrium constant of the water-gas homogeneous reaction. Such correlations were established using results obtained from the application of an optimization method (AOM) that uses Kuhn–Tucker multipliers. Syngas compositions determined through AOM were compared with experimental compositions and those estimated by other models, resulting that the AOM always determines the best estimates with respect to the root mean square error (RMSE). For syngas compositions estimated by AOM, the RMSE interval is [0.21, 4.11]. The PM was validated with six experimental compositions. From the predicted syngas compositions it was found that the ranges for LHV, cold gas efficiency, carbon conversion efficiency and gasification temperature were [4.594, 5.116 MJ/Nm3], [55.74, 68.18%], [74.20, 88.40%] and [749, 918 °C], respectively. Additionally, for the predicted syngas compositions the RMSE interval was determined as [0.68, 2.25]. Therefore, the PM was considered to be effective in estimating syngas compositions

Experimental determination of lower flammability limits of Synthesized Iso-Paraffins (SIP), jet fuel and mixtures at atmospheric and reduced pressures with air

The creation of alternative fuels to reduce CO2 emissions in the aeronautical sector necessitates the determi- nation of their safety properties, among which are their Flammability Limits. Synthesized Iso-Paraffins (SIP) are blending components that have already been approved for blending with traditional aviation fuel by up to 10 vol %. Therefore, this manuscript is aimed at experimentally determining the Lower Flammability Limit (LFL) of SIP, jet fuel and mixtures of 10% (F10) and 50% (F50) in mass of SIP at atmospheric and reduced pressures with air. For this purpose, an experimental bench was built in accordance with American Society for Testing and Mate- rials, ASTM E681. The LFL of the samples was initially determined at a pressure of 101.3 kPa and high tem- peratures. Afterward, the LFL of samples was determined at reduced pressures, i.e. 80, 60, 40 and 20 kPa, and also high temperatures. For this analysis, 316 tests were performed. For a better understanding of the experi- mental results, additional material is attached, presenting the temperatures and the volumes used in carrying out each test. Finally, adjustment equations based on the experimental results of this manuscript for SIP, jet fuel, and their mixtures, were presented as a function of temperature and atmospheric pressure