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Session XXXX

Solving Combustion Problems using the First and Second Laws of Thermodynamics with Applications for the Classroom

Mehmet Sözen, Michael R. Sexton

Embry-Riddle Aeronautical University / Virginia Military Institute

Abstract

The paper discusses the implementation of a unified approach for solving combustion problems by applying the first and second laws of thermodynamics simultaneously with applications for the classroom. The model was developed for the combustion of hydrogen and oxygen using ideal gas mixture assumption for the reactants and combustion products, and was based on chemical equilibrium assumption. The authors implemented the second law (minimization of Gibbs free energy) in two different but equivalent methods: one used chemical equilibrium constants as functions of temperature correlated from data tables, and the other computed the equilibrium constants using the change in Gibbs free energy computed from elementary thermodynamic properties. The latter method was implemented using MathCad for the solution of the problem. Solutions were obtained for fuel to oxygen ratios covering fuel rich to fuel lean conditions. These solutions were compared with those obtained using a FORTRAN code based on the first approach and originally reported by Sözen and Majumdar [1] at the 2004 ASEE Annual Conference. Excellent agreement was found between the two solution methods. It was demonstrated that MathCad provides a powerful tool in implementing this approach to the solution of combustion problems for use in a course in thermodynamics, at the undergraduate level, or in an introductory course in the theory of combustion. The paper reports classroom experience using the MathCad model as a teaching/learning tool to teach combustion in a second semester thermodynamics course taught in the Fall of 2004.

Introduction

The idea and the need for this work came from the fact that in most elementary engineering thermodynamics textbooks [2-5] the standard types of problems dealing with chemical reaction/ combustion, and chemical equilibrium are limited in scope. The dissociation reactions that produce radicals are mostly ignored. An exception is seen in Ref. 2, where, only a single dissociation reaction is considered. With such simplified approach, most combustion problems are solved from a purely conservation of energy principle consideration. Similarly in chemical equilibrium problems considered, the combustion product temperature is usually provided and the composition of the combustion products is then determined by the use of chemical equilibrium constants. It is, however, important in system level design of a complete propulsion

Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition Copyright © 2005, American Society for Engineering Education

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Sexton, M. R., & Sozen, M. (2005, June), Solving Combustion Problems Using The First And Second Laws Of Thermodynamics With Applications For The Classroom Paper presented at 2005 Annual Conference, Portland, Oregon. 10.18260/1-2--15246