Combustion Toolbox: An open-source thermochemical code for gas- and condensed-phase problems involving chemical equilibrium
Abstract
We present a new thermochemical code—hereafter referred to as Combustion Toolbox (CT)—for the solution of problems that involve chemical equilibrium of gas- and condensed-phase species. The kernel of the code is based in the theoretical framework set forth by NASA’s computer program CEA (Chemical Equilibrium with Applications), while incorporating new algorithms that result in a significant speed up of the convergence rate. The thermochemical properties are computed under the ideal gas approximation using an up-to-date version of NASA’s 9-coefficient polynomial fits. These fits use the Third Millenium Database which includes the available values from Active Thermochemical Tables. Combustion Toolbox is programmed in MATLAB with a modular architecture composed of three main modules: CT-EQUIL, CT-SD and CT-ROCKET. The core module, CT-EQUIL, minimizes the Gibbs/Helmholtz free energy of the system using the technique of Lagrange multipliers combined with a multidimensional Newton-Raphson method, upon the condition that the mixture properties are defined by two functions of state (e.g., enthalpy and pressure). CT-SD solves processes that involve strong changes in the dynamic pressure, such as steady shock and detonation waves under both normal or oblique incidence angles within the limits of regular shock reflections. Finally, CT-ROCKET estimates rocket engine performance under ideal conditions. The new tool is equipped with a versatile Graphical User Interface and has been successfully used for both teaching and research activities during the last three years. Results are in excellent agreement with CEA, CANTERA within Caltech’s Shock and Detonation Toolbox (SD-Toolbox), and the recent Thermochemical Equilibrium Abundances (TEA) code. CT is available under an open-source GPLv3 license via Github https://github.com/AlbertoCuadra/combustion_toolbox and its documentation can be found in https://combustion-toolbox-website.readthedocs.io.
