equilibrium-c: A Lightweight Modern Equilibrium Chemistry Calculator for Hypersonic Flow Applications

TL;DR

equilibrium-c is a lightweight, efficient C-based tool with a Python interface for computing chemical equilibrium in gas mixtures, suitable for hypersonic flow and multi-physics applications.

Contribution

the paper introduces a minimal dependency, easily embeddable chemical equilibrium solver with verified and validated performance for fluid dynamics and combustion.

Findings

minimal dependencies and easy integration

verified accuracy through example problems

applicable to hypersonic flow simulations

Abstract

equilibrium-c (eqc) is a program for computing the composition of gas mixtures in chemical equilibrium. In typical usage, the program is given a known thermodynamic state, such as fixed temperature and pressure, as well as an initial composition of gaseous species, and computes the final composition in the limit of a large amount of time relative to the reaction speeds. eqc includes a database of thermodynamic properties taken from the literature, a set of core routines written the C programming language to solve the equilibrium problems, and a Python wrapper layer to organise the solution process and interface with user code. Dependencies are extremely minimal, and the API is designed to be easily embedded in multi-physics codes that solve problems in fluid dynamics, combustion, and chemical processing. In this paper, I first introduce the equations of chemical equilibrium, then spend some time discussing their numerical solution, and finally present a series of example problems, with an emphasis on verification and validation of the solver.