Estudo e desenvolvimento numérico do projeto de um gerador elétrico acionado por motor a pistão livre

Abstract

Due to the constant restrictions, that regulate the level of pollutants emissions, on the market, the demand for more efficient alternatives for the conventional generators has increased, mainly those which energy source are fossil fuels. The Free-Piston Engine is one of those alternatives, as a concept that despite of the loss of popularity in the 60th of the last century, has attracted the attention of the research centers in recent years. It presents as advantages higher efficient, compactability, simplicity and easier maintainability, as well as the possibility of variable compression ratio. Those features justify the scientific effort made on this equipment. The assembly of a Free-Piston Engine and a Linear Electric Generator is denominated as Free-Piston Generator, which applicability in hybrid vehicles or as energy generator are widely referred. The objective of this work is to develop a mathematical and numerical model of a Free-Piston Generator for design and optimization purposes. Distinctly of the models available in the literature, the developed model must consider the relation between the Free-Piston Engine and the Linear Generator in a way that the dimensions and parameters of the electric element are also available for the final user. To achieve this goal, a model of a permanent magnetic electric generator is derived using a semi-analytical method, namely Subdomains Method, in order to estimate the magnetic field distribution in the interior of the machine. The results of the model were validated and compared with a Finite Element Method based model, and this comparison highlighted the advantages of the chosen method: the low-computational cost and small errors. To simulated the thermodynamic phenomena that are present in the Free-Piston Engine, a zero-dimensional model is derived from the First Law of Thermodynamics combined with inherent assumptions of the ideal gases theory. The derived model was validated by comparison with a more sophisticated model, namely Homogeneous Two-Zone Finite Release Cycle. The electromagnetic and thermodynamic models are associated with a third model, the dynamic model, derived from the Newton’s Second Law, in order to obtain the complete coupled model and meet the objetiv. To illustrate the capability of the obtained model, a set of parametric analysis are made and observations on the relation between the variables of the model are done. At the end, a procedure for design a Linear Free-Piston Generator using the proposed model is described.