Aplicação de métodos adaptativos para a simulação de processos de combustão

Muitos dos modelos que envolvem combustão, nomeadamente da reacção da termite Fe2O3/Al, inserem-se numa classe de problemas cuja solução consiste na propagação de frentes abruptas de reacção exotérmica com dinâmica altamente não linear. Por outro lado, verifica-se a ocorrência de problemas de instabilidade (pulsação da frente, formação de modos de propagação rotacionais, etc), quando o valor de alguns parâmetros ultrapassa valores críticos. Dadas as condições extremas a que ocorrem as referidas reacções e à grande incerteza associada à estimativa de parâmetros importantes, esta classe de modelos constitui-se como um caso de estudo interessante para o teste de uma grande variedade de métodos numéricos adaptativos de integração (para geometrias uni- e multidimensionais). Deste modo, no presente trabalho aplica-se um método de adaptação de malha para a resolução de um modelo unidimensional que descreve o processo de combustão do sistema Fe2O3/Al. Conclui-se que o termo reactivo não se revela suficiente para auto-sustentar a propagação da frente, verificando-se um fenómeno de abrandamento e aceleração sucessivos, determinado pela competição entre as influências da condução de calor induzida pela condição fronteira e do calor libertado pela reacção. Conclui-se também ser necessária a análise mais aprofundada dos parâmetros e considerações do modelo e dos parâmetros numéricos, para uma descrição física mais consentânea com as características destes fenómenos. Pretende-se ainda futuramente estender o presente estudo a modelos de geometria radial bidimensionais, utilizando o método descrito e outros mais complexos – adaptação dinâmica e wavelets

Ignition of a Ti-Al-C system by an electron beam

This paper describes the optimal modes of initiation of self-propagating hightemperature synthesis with the help of an electron beam on the example of a Ti-Al-C powder mixture. A pulsed electron beam with a particle energy of tens of kiloelectronvolts and a duration of hundreds of microseconds is used. Morphology, structure, and elemental composition of formed products in the form of Ti3AlC2 and TiC are studie

A study of ignition and propagation of combustive synthesis reaction between titanium and carbon

Combustive Synthesis or Self-Propagating High-Temperature Synthesis (SHS), is an energy-efficient combustion method of producing metallic, ceramic and composite materials from their constituent powders. This thesis presents the results of an experimental and numerical evaluation of the propagation velocity for the SHS solid-solid reaction of titanium and carbon, as well as a study of the ignition process for the reaction. The experimental results show the dependency trend of the wave propagation speed on various parameters: diameter of the reactant compact, density of the compact, reactant mixture composition, and dilution of the reactant mixture with the inert product TiC. Conditions at which the reaction ceases to propagate in a self-supporting manner are also identified. This thesis attempts to generalize the existing experimental observations of the gasless SHS process by means of a dimensional analysis, thus offering a mechanistic framework within which future developments can be correlated. The implementation of the new reaction kinetics model of Kanury and some suitable dimensionless variables permit the main factors affecting the process to be embedded in a single key parameter, the Da number. This parameter includes the overall effects of thermal properties, stoichiometry of the reaction, carbon particle size, a process constant, a compression effect and the diffusion of one reactant through an intermediate complex. The study of propagation covers a broad range of possible Da numbers that could arise for different conditions found in experiments. A section in numerical calculations of the preheated length is included as well. Comparison of the numerical and experimental results for propagation are found to be in reasonable agreement, thus validating the suitability of the analytical model. The numerical study includes an examination of the ignition problem for a stoichiometric mixture, using a prescribed surface temperature boundary condition. For this condition, an ignition threshold curve is determined above which ignition will always occur and below which no ignition is possible

Dynamics of Patterns

Patterns and nonlinear waves arise in many applications. Mathematical descriptions and analyses draw from a variety of fields such as partial differential equations of various types, differential and difference equations on networks and lattices, multi-particle systems, time-delayed systems, and numerical analysis. This workshop brought together researchers from these diverse areas to bridge existing gaps and to facilitate interaction

Fifth International Microgravity Combustion Workshop

This conference proceedings document is a compilation of 120 papers presented orally or as poster displays to the Fifth International Microgravity Combustion Workshop held in Cleveland, Ohio on May 18-20, 1999. The purpose of the workshop is to present and exchange research results from theoretical and experimental work in combustion science using the reduced-gravity environment as a research tool. The results are contributed by researchers funded by NASA throughout the United States at universities, industry and government research agencies, and by researchers from at least eight international partner countries that are also participating in the microgravity combustion science research discipline. These research results are intended for use by public and private sector organizations for academic purposes, for the development of technologies needed for the Human Exploration and Development of Space, and to improve Earth-bound combustion and fire-safety related technologies

Microgravity Combustion Research: 1999 Program and Results

The use of the microgravity environment of space to expand scientific knowledge and to enable the commercial development of space for enhancing the quality of life on Earth is particularly suitable to the field of combustion. This document reviews the current status of microgravity combustion research and derived information. It is the fourth in a series of timely surveys, all published as NASA Technical Memoranda, and it covers largely the period from 1995 to early 1999. The scope of the review covers three program areas: fundamental studies, applications to fire safety and other fields. and general measurements and diagnostics. The document also describes the opportunities for Principal Investigator participation through the NASA Research Announcement program and the NASA Glenn Research Center low-gravity facilities available to researchers

The combustion of titanium powder in air and iron oxide

The quest for ever stronger and tougher steels has lead to an interest in the 'Acicular Ferrite' microstructure, its chaotic and disordered morphology imparting a high degree of toughness to the steel. To date, only complex and expensive materials and manufacturing processes have formed acicular ferrite within bulk cast steel. As such, the thrust of this research is to produce a cheap steel addition, an iron - titanium oxide metal-ceramic composite, that will facilitate the formation of acicular ferrite in conventionally manufactured bulk cast steels. The Self-propagating High-temperature Synthesis (SHS) process has been utilised to manufacture the iron - titanium oxide material from compacts pressed from Fe203 + Ti powders. The fundamental reactions that occur as titanium powder and Fe203 + Ti powder compacts are heated in air and argon atmospheres have been investigated. The process’s involved are reported and have been modelled mathematically. A computer simulation of the reaction process has been developed and tested against experimental evidence. The effect of various compact parameters, the starting compact stoichiometry and other processing variables have been examined with respect to the composition of the products and their morphology

The combustion of titanium powder in air and iron oxide

The quest for ever stronger and tougher steels has lead to an interest in the 'Acicular Ferrite' microstructure, its chaotic and disordered morphology imparting a high degree of toughness to the steel. To date, only complex and expensive materials and manufacturing processes have formed acicular ferrite within bulk cast steel. As such, the thrust of this research is to produce a cheap steel addition, an iron - titanium oxide metal-ceramic composite, that will facilitate the formation of acicular ferrite in conventionally manufactured bulk cast steels. The Self-propagating High-temperature Synthesis (SHS) process has been utilised to manufacture the iron - titanium oxide material from compacts pressed from Fe203 + Ti powders. The fundamental reactions that occur as titanium powder and Fe203 + Ti powder compacts are heated in air and argon atmospheres have been investigated. The process’s involved are reported and have been modelled mathematically. A computer simulation of the reaction process has been developed and tested against experimental evidence. The effect of various compact parameters, the starting compact stoichiometry and other processing variables have been examined with respect to the composition of the products and their morphology