Assessing the CFD applicability of chemical kinetic mechanisms for pure ammonia combustion

Abstract

Ammonia is a promising carbon-free fuel, but realising its potential for green energy requires combustion models that are both accurate and computationally efficient. While many reaction mechanisms have been proposed, few are designed with computational fluid dynamics (CFD) applications in mind. This study evaluates 11 mechanisms based on their predictions of laminar flame speed, peak flame temperature, NO emissions, computational cost, and minimum species timescales. One-dimensional flame simulations across equivalence ratios from 0.5 to 1.5 identified three different mechanisms as the most promising, though each showed trade-offs in computational cost, NO prediction, or laminar flame speed accuracy. Random forest regression showed that the minimum species time scale is a key factor for solution time, on par with the number of reactions. Mechanisms with OH* sub-mechanisms produced very short time scales, potentially limiting their CFD applicability. Overall, the results highlight the need to balance computational cost and accuracy in mechanism selection, and call for further development of reduced mechanisms that address CFD-relevant metrics, such as the minimum species time scale