Accuracy and convergence rate of steady-state simulation of one-dimensional, reactive gas flow with molar expansion

A coupled and a decoupled solution method are applied to the steady-state simulation of one-dimensional, reactive gas flow. The accuracy of the numerical steady-state solution depends to a significant extent on the molar expansion of the gas. The convergence rate of the coupled solution method is almost independent of molar expansion. The convergence rate of the decoupled solution method is at least 50% lower for strong molar expansion than for nonexistent molar expansion. By adding a transport equation for molar mass, the convergence rate of the decoupled solution method becomes almost independent of molar expansion. The results for the decoupled solution method apply to other methods in which composition is determined on a fixed flow field. A tool is presented to quantify the perturbation of the flow field by the chemical reactions.

► We simulate flow with varying molar expansion and compare to an analytical solution.
► Accuracy of steady-state solution decreases with increasing molar expansion.
► Convergence rate of coupled solver independent of molar expansion.
► Convergence rate of decoupled solver at least 50% lower for strong molar expansion.
► Convergence rate of decoupled solver improved significantly by adding a new equation.