The fact that there is an increase in the price of fossil fuels, and that environmental changes are occurring due to pollutant emissions, makes it imperative to find alternative fuels that are less polluting and cheaper. Gas turbines have been particularly developed as aviation engines, but nowadays they can find applicability in many areas and the fact that they have multiple fuel applications, makes them a very important subject of study. The main objective of this dissertation is to evaluate through a CFD analysis on FLUENT the performance of the combustion in a gas turbine can combustor, fed with methane, hydrogen and methane-hydrogen mixtures taking a particular interest in the pollutants emissions. In the end a fuel optimization was carried on to evaluate the average mass fraction of the pollutants CO, CO2 and NOx at the exit of the can combustor, and also a brief evaluation of the static temperature and pressure, and velocity magnitude in the several CFD simulations was executed.

The aeronautical sector needs to introduce alternative fuels in order to achieve a reduction in greenhouse gas emissions. A possible solution in the near future might be the blending of biofuels with jet fuel, which would allow the use of a greener fuel without significant changes in the existing fleets of the companies, which means the development of a “drop in” fuel. The present work aims to study the ignition and combustion characteristics of single droplets of jet-A1 (JF), hydroprocessed vegetable oil (NExBTL) and their mixtures in a drop tube furnace (DTF). The droplets were injected into the DTF using a droplet generator. Experiments were conducted in air for three DTF wall temperatures (900, 1000 and 1100 ºC). The ignition and combustion of the droplets were evaluated through the images obtained with a high-speed camera coupled with a high magnification lens. The images allowed for the observation of the burning phenomena, and data are reported for temporal evolution of droplet sizes and burning rates. The results revealed that the mixtures followed the 2 law, except the mixture with 75% JF for a DTF wall temperature of 1100 ºC. This was due to the occurrence of puffing, which enhanced the burning rates. In addition, it was observed that the mixtures with higher content of JF present brighter flames, and higher burning rates.

The pursuit of enhanced propulsion system performance has driven the development of combustion technologies operating at increasingly higher pressures. Such conditions tipically exceed the thermodynamic critical thresholds of the propellants, giving rise to complex transcritical and supercritical flow regimes. The oxygen/hydrogen propellant combination has been extensively and successfully employed in liquid rocket propulsion, and, in the context of global decarbonization objectives, the clean, high-energy characteristics of hydrogen make it a promising candidate for future propulsion applications extending beyond rocketry. The modeling of shear coaxial injection of oxygen and hydrogen under supercritical conditions is addressed through a steady-state axisymmetric Favre-averaged Navier-Stokes formulation, with combustion treated using the Eddy-Dissipation-Concept model in conjunction with a detailed kinetic mechanism consisting of eight species and nineteen elementary reactions. The near-field region of the injector constitutes the primary focus of this work, as it is within this zone that the mixing efficiency is established, ultimately governing the overall combustion and engine performance. The simulations are carried out piecewise to ensure consistency thorugh all the simulation process. Firstly, non-reacting simulations are performed, incorporating both ideal- and real-gas models. After that, reacting simulations are performed in order to validate the developed numerical model against experimental data. Two main innovative contributions distinguish the present study from previous works on O2/H2 coaxial injection. The first concerns computational efficiency, achieved through a substantial reduction of the chamber length to the minimum extent necessary to ensure that the outlet boundary conditions do not affect the near-field region. In addition, the omission of the low-velocity recirculation zone located above the injector head was implemented to further reduce computational cost. The second innovation involves the inclusion of heattransfer effects in both the injector and chamber walls. In particular, the influence of the isothermal walls configuration on the injector is analyzed in light of the thermal disintegration mechanism of the inner jet, previously identified in the literature for cold-flow conditions under supercritical regimes. The numerical results demonstrated the capability of the developed framework to accurately model cryogenic O2/H2 injection and combustion under supercritical conditions. The non-reacting simulations established a robust numerical foundation and captured the key flow features, including the dense oxygen core and the surrounding high-velocity hydrogen stream. The incorporation of real-gas effects proved essential, as the ideal-gas assumption led to significant deviations in core length and mixing behavior. In the reacting regime, the real-gas model reproduced the experimental axial temperature profile and flame structure with good accuracy, outperforming the ideal-gas formulation and yielding results comparable to those reported in the literature, thereby confirming its suitability for high-pressure combustion modeling.

The environmental impact and the dependence upon fossil fuels in the aeronautical sector have promoted the demand for alternative and greener fuels. The implementation of alternative fuels is one of the main challenges for this sector in the near future. A possible short-term solution might be the blending of biofuels with jet fuel, which would allow for the use of greener fuels and a reduction in the greenhouse gases and pollutant emissions without significant changes in the existing fleets of the companies, with the purpose to develop a “drop-in” fuel. In this context, this work examines the combustion characteristics of single droplets of Jet A-1 (JF), hydroprocessed vegetable oil (NExBTL), and their mixtures in a drop-tube furnace (DTF). The objective of this work is to evaluate the influence of the mixture composition on the fuel characteristics. Droplets with diameters of 155 ± 5 μm, produced by a commercial droplet generator, were injected into the DTF, whose wall temperature and oxygen concentration were controlled. Experiments were conducted for three temperatures (900, 1000, and 1100 °C). The combustion of droplets was evaluated through the images obtained with a high-speed camera coupled with a high magnification lens and an edge detection algorithm. From the images allowed for the analysis of droplet combustion, data are reported for the temporal evolution of droplet sizes and burning rates. The results revealed that the mixtures followed the D2 law, except the mixture with 75% JF for a DTF wall temperature of 1100 °C. The 75% JF mixture did not follow the D2 law as a result of the occurrence of puffing and microexplosions, which enhanced the burning rates. Additionally, it was observed that the mixtures with a higher content of JF present brighter flames and higher burning rates.

This study examines the burning characteristics and disruptive burning phenomena of single droplets of aluminum nanoparticles (n-Al) stably suspended in a biofuel (HVO). The biofuel used in the present work is a promising alternative fuel already tested in the aviation sector to reduce greenhouse gas and pollutant emissions. Experiments were conducted with two particle sizes (40nm and 70nm) and two particle concentrations (0.5 wt.% and 1.0 wt.%) to study its influence when added to the biofuel. The effect of size and concentration of the aluminum nanoparticles was studied at 1100 °C in a drop tube furnace. This experimental facility allows the study of combustion characteristics of falling droplets, ensuring there is no influence of the supporting fiber on the burning rate and disruptive burning phenomena occurrence. A CMOS high - speed camera coupled with a high magnification lens was used to evaluate the droplet size, burning rate, and micro-explosions. Based on this procedure, pure biofuel droplets were compared with those of biofuel blended with nanoparticles. The results suggest that the combustion characteristics of pure HVO can be enhanced with the addition of aluminum nanoparticles. Furthermore, by decreasing the particle size, a slight increase in the burning rate of nanofuels was noticed. Additionally, an increase in the particle concentration leads to a pronounced increase in the burning rate. The particle concentration also influences the delay and intensity of micro-explosions, disruptive burning phenomena detected at the end of the droplet lifetime.

A necessidade em diminuir as emissões de poluentes causados pela queima de combustíveis fósseis, levou a busca por alternativas para diminuir a dependência dos combustíveis de petróleo e reduzir as emissões de poluentes. O biodiesel é visto como um combustível capaz de diminuir o consumo do diesel de petróleo, tanto é que desde o ano de 2008 é adicionado uma fração do biodiesel no diesel de petróleo comercializado nos postos de gasolina e essa fração vem aumentando com o passar do tempo. Devido às vantagens que o biodiesel oferece e sua complexidade, um estudo teórico relacionado ao processo de ignição e combustão se mostram necessários. No entanto, um estudo teórico das reações de ignição do ésteres de ácidos graxos é computacionalmente inviável. Por este motivo, estudar a combustão de pequenas moléculas de ésteres metílicos, como por exemplo, o etanoato de metila (EM) pode ser de grande importância para o entendimento do processo de ignição de ésteres superiores. A combustão é fortemente afetada pelo atraso de ignição, que se inicia pela abstração de um hidrogênio do combustível, seguido de outras reações envolvendo radicais livres, e sua descrição detalhada pode auxiliar no desenvolvimento de modelos cinéticos melhorados para combustão do biodiesel. Com este objetivo, foram feitos cálculos utilizando a teoria do funcional da densidade (DFT) e teoria do estado de transição para obtenção dos parâmetros termodinâmicos e cinéticas que regem a abstração de hidrogênio do EM por radicais O, OH, HO2, H e a molécula de O2. Foram utilizados os funcionais B3LYP-D3 e M06-2X com os conjuntos de base cc-pVDZ, cc-pVTZ, aug-cc-pVDZ e aug-cc-pVTZ para avaliação do efeito da metodologia no cálculo de parâmetros termodinâmicos e cinéticos. Posteriormente, foram feitos cálculos single-point em nível CCSD(T)/cc-pVTZ considerando os parâmetros geométricos obtidos em nível M06-2X/aug-cc-pVTZ e recalculados os coeficientes de velocidade no intervalo de 250-3500K considerando as frequências vibracionais calculadas em DFT. Correções de tunelamento, rotor impedido das metilas e efeitos de anarmonicidade também foram incluídos nos cálculos dos coeficientes de velocidade. Os resultados a 298K e as equações de Arrhenius obtidas mostram que o funcional B3LYP-D3 superestima consistentemente os parâmetros cinéticos em relação ao funcional M06-2X. A análise da metodologia apontou que a escolha do funcional tem maior efeito nos resultados do que a escolha da base e que bases do tipo double-zeta não são suficientes para cálculo de coeficientes de velocidade precisos. A inclusão do efeito da anarmonicidade se mostrou importante para o calculo de k(T) em todo intervalo de temperatura, sendo este responsável pela diminuição dos coeficientes calculados.

In this work compounds Zn1-xFexO, with 0.00 ≤ x ≤ 0.09, were synthesized by combustion reaction method with two different heating processes, in a thermal blanket and muffle furnace. Chemical analysis of compounds was performed by atomic absorption spectroscopy (AAS) and Fourier transform infrared (FTIR). Structural analysis of the crystalline phase, the diameter of the crystallites and the lattice parameters were checked by X-ray diffraction (XRD, powder method) and refinement software (Unitt and powder X cell). The analysis of surfaces and morphologies were determined by adsorption and desorption of N2 (ASAP, BET model) and transmission electron microscopy (TEM). Finally, Magnetic measurements were performed by vibrating sample magnetometer (VSM). The stoichiometric determined by atomic absorption is in good agreement with the calculated value for all samples. The samples were synthesized in a thermal blanket which corresponds to the wurtzite crystal structure with no secondary phases. The samples synthesized in furnace had wurtzite crystal structure, however, showed a small sample to phase segregation above 5%. The second phases are found with spinel phase indicate that the formation of zinc ferrite. The data of thermal analysis, infrared and X-ray diffraction, we show that the synthesis product in blanket form moving slowly in several stages, while that in the synthesis furnace gets the product directly. We noted the tendency of the formation of smaller particles for the samples from the thermal blanket, as well as high surface areas for these samples, those prepared in a muffle grating. Images by transmission electron microscopy confirm the observations made by x-ray diffraction measurements of surface areas by BET model. The magnetic measurements show ferromagnetic phenomenon only for the sample produced in a muffle. The saturation magnetization was calculated by extrapolation, and their values are promising when compared with the literature. The Curie temperatures were estimated for some samples and all values were well above room temperature.

Combustion is currently the main method to produce energy in the world energy matrix. Through the burning of oil, coal and natural gas, mankind supplies its energy needs while migrating in a balanced way to renewable energy sources. From this context comes the need for efficient control of combustion, a key process in reducing the consequences of the greenhouse effect, and hence an accurate measurement of CO2 and O2 emissions in combustion processes. Due to the hostile process conditions such as high temperature, difficult access to the controlled area and the risk of explosion, the use of sensors on the flame is often impractical and image monitoring has proven to be a convenient alternative. In this paper, an inference device based on artificial neural networks that uses monochromatic flame images captured by a CCD (chargedcoupled device) camera is designed to estimate CO2 and O2 emissions in a natural gas furnace. The proposed method seems promising: it estimates without delay, unlike traditional gas analyzers, and with good accuracy on the tested equivalence ratios (root mean square error below 2%)

Recentemente um novo regime de queima de gotas, conhecido como regime “cool flame”, tem sido alvo de investigação por apresentar características diferentes da queima convencional. No regime cool flame a combustão ocorre em duas fases distintas. Na primeira, a gota sofre uma queima normal, com uma chama visível em torno da mesma. Na segunda, a radiação luminosa da chama se extingue, porém, a gota permanece vaporizando sem chama visível e com uma temperatura mais baixa. Além disso, a gota apresenta uma taxa de vaporização praticamente igual a primeira fase. No final da segunda fase, uma nuvem de vapor é formada em torno da gota. Simulações numéricas de cinética química atribuem essa nuvem como sendo resultado do combustível não queimado pela chama. Com a ideia de combustível não queimado, o presente modelo tem por finalidade utilizar um modelo clássico de queima de gotas e impor um escape de combustível pela chama, processo que é um dos efeitos apontados como responsável por manter a chama no regime de cool flame. O modelo clássico é baseado na hipótese de chama estreitamente fina onde o combustível e o oxidante são totalmente consumidos, permitindo que o modelo de Shvab- Zeldovich seja utilizado sem a necessidade de envolver a cinética química no modelo. Os resultados mostram que com o aumento do escape de combustível a temperatura da chama diminui e a chama se aproxima da gota. Porém, a taxa de vaporização, não é tão sensível ao aumento de escape de combustível mantendo-se praticamente constante. Estes comportamentos estão de acordo com análises experimentais observadas no regime cool flame. Considerando um escape de combustível elevado, é possível encontrar a chama a uma distância medindo cinco vezes o raio da gota, coincidindo com os resultados obtidos por modelos de cinética química. Contudo, apesar desses dados concordarem com os obtidos experimentalmente, o modelo é limitado, pois o ecape de combustível é imposto pelo modelo, enquanto que deveria ser uma incógnita a ser resolvida. Mesmo assim, o modelo é útil para estimar parametricamente o comportamento das propriedades em função do escape de combustível pela chama.