CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A âCombustÃo de FiltraÃÃoâ à uma tecnologia que tem sido empregada no desenvolvimento de aquecedores e caldeiras de alta eficiÃncia e baixa emissÃo de poluentes. No entanto, o processo de igniÃÃo da combustÃo nesses equipamentos, constituÃdos de queimadores porosos volumÃtricos, tem sido ainda uma questÃo nÃo resolvida. Os sistemas convencionais desenvolvidos para esses queimadores apresentam algum inconveniente operacional que prejudica a eficiÃncia de combustÃo. EntÃo, este trabalho tem como objetivo principal apresentar um projeto robusto e econÃmico de sistema de igniÃÃo por lanÃa-chamas destinado a queimadores porosos volumÃtricos, em que a CombustÃo de FiltraÃÃo està sendo aplicada como tecnologia de base para desenvolvimento de um novo modelo de aquecedor de Ãgua. Um protÃtipo do aquecedor equipado com o sistema de igniÃÃo foi desenvolvido, em escala de laboratÃrio, realizando-se estudos experimental e teÃrico quanto à queima com gÃs natural e com biogÃs. A anÃlise teÃrica envolve a caracterizaÃÃo do escoamento dos gases ao longo do corpo do sistema de igniÃÃo atravÃs da simulaÃÃo com o software âANSYS-CFXâ, como tambÃm, dos fenÃmenos relacionados à onda de combustÃo propagando-se no queimador do aquecedor, para o qual foi utilizado um modelo numÃrico de simulaÃÃo em FORTRAN. Neste contexto, à utilizado o software PREMIX no cÃlculo de equilÃbrio quÃmico, aplicÃvel à combustÃo prÃ-misturada em um meio poroso, tomando como referÃncia os dois parÃmetros principais de operaÃÃo: a razÃo de equivalÃncia e a velocidade do escoamento da mistura ar-combustÃvel. Como resultado: o sistema de igniÃÃo proposto mostrou-se adequado aos queimadores porosos, provendo estabilidade e facilidade de operaÃÃo, e reduzindo significativamente o tempo necessÃrio ao prÃ-aquecimento do meio poroso. O modelamento do escoamento e da combustÃo serviu de suporte para interpretaÃÃo adequada dos fenÃmenos presentes nos processos. A CombustÃo de FiltraÃÃo possibilitou a operaÃÃo estÃvel do aquecedor em ampla faixa de razÃo de equivalÃncia (de 0.30 a 1). / "Filtration Combustion" is a technology that has been used in the development of heaters and boilers with high efficiency and low pollutant emissions. However, the ignition process of combustion in such equipments, constituted of volumetric porous burners, have been an issue still unresolved. Conventional systems developed for these burners present some operational drawback that affects the combustion efficiency. So, this work aims mainly to present a robust and economical design of flame-thrower ignition system aimed at volumetric porous burners, in which Filtration Combustion is being applied as a basis technology for the developing a new model of water heater. A prototype of the heater equipped with the ignition system has been developed in laboratory scale, carrying out experimental and theoretical studies on the burning natural gas and biogas. The theoretical analysis involves the characterization of gas flow along the body of the ignition system through simulation with the software "ANSYS-CFX," as well as of the phenomena related to the combustion wave propagating itself through the heaterâs burner, for which a numerical simulation in FORTRAN has been used. In this context, a software âPREMIXâ was used in the chemical equilibrium calculation, applicable to premixed combustion in a porous medium, taking as reference the two main parameters of operation: the equivalence ratio and flow velocity of the air-fuel mixture. As a result, the ignition system proposed has been adequate to the porous burner, providing stability and ease of operation, and significantly reducing the time required for preheating the porous medium. The modeling of flow and combustion has served as a support for proper interpretation of the phenomena present in the processes. Filtration Combustion has allowed stable operation of the heater in a wide range of equivalence ratio (from 0.30 to 1).

The dissertation thesis is focused on the investigation of the influence of inert gases on characteristic parameters of the combustion process. Inert gases are usually standard components of alternative gaseous fuels such as the producer gas, coal gas or biogas. For a long period some of the fuels were considered as waste gases and their potential was not sufficiently utilised. Compared with noble fuels such as natural gas, alternative fuels have different physical-chemical properties. For example, their lower heating value (LHV) can be lower even than 10 MJ/mN3. The composition of the alternative gaseous fuels can be various during their production process. Lower LHV is a result of the occurrence of inert gases that does not take a part in the combustion reactions. Inert gases have the ability to accumulate the heat. Under certain conditions it is possible to combust alternative fuels on conventional burners, but due to their different properties, problems can occur during the combustion. E.g. to achieve the same heat output as with the noble fuel, it is necessary to burn bigger volume of the alternative fuel. However, the limiting factor could be the burner's head geometry. Theoretical introduction of the thesis summarizes research results in the field of low calorific gaseous fuels combustion and the addition of inert gases into the noble fuels. The thesis also describes the mechanisms of the NOx formation and summarizes techniques which can be used to reduce NOx formation. Furthermore, fuels from alternative sources are categorized and described, including their composition and characteristics. Their physical-chemical properties were obtained by means of the combustion simulation carried out in the simulation software. Two devices had to be designed and manufactured to fulfil goals of the dissertation thesis. The first is a gas mixing station capable of mixing 4 different components. The second device is a burner utilized for the combustion of low calorific fuels. The key section of this thesis is a chapter describing the experimental plan, the performance and the evaluation of the experiments. The goal of the experiments was to dilute the natural gas by two inert gases, namely carbon dioxide and nitrogen. The lowest LHV value achieved during the experiment was 10,7 MJ/mN3. The influence of the inert gases on the NOx emissions, the flame stability and characteristics, the flue gas temperature, the in-flame temperatures, the heat flux and the thermal efficiency was investigated and evaluated. Each parameter was measured and evaluated for three different burners: the burner with the staged gas, the burner with the staged air and the burner for low calorific fuels. Generally, after the addition of the inert gas into the noble fuel, the in-flame temperatures decreased. As a consequence, the NOx emissions decreased as well. The effects of carbon dioxide on the investigated combustion parameters were more substantial than the effects of nitrogen. Each measured parameter is strongly dependent on the burner geometry. The experiments revealed that in most cases the addition of the inert gas into the fuel influenced the flame length (flame shortened) and also more heat was transfered into the chamber's walls closer to the burner tile.

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This master’s thesis deals with flame detection methods. The purpose of the project was to create a flame detector, which uses the alternative method of flame detection. The introduction of this thesis gives the summary overview of the existing methods for flame detection. Further, the existing flame detectors and their applications are described. Two alternative algorithms for flame detection which are based on the digital signal analysis were realized on the PC. Flame detector, which utilizes the digital analysis of audio signal, was realized on 8 bit microcontroller Atmega128 and achieved results are presented.