FGM modeling of ammonia/n-heptane combustion under RCCI engine conditions

Abstract

A novel flamelet-generated manifold (FGM) model is introduced, encompassing ignition and flame propagation in ammonia/n-heptane dual-fuel combustion under reactivity-controlled compression ignition (RCCI) engine conditions. To generate the FGM mapping function (FGM tabulation) accounting for multiple combustion modes in RCCI combustion, a novel one-dimensional RCCI configuration (1D-RC) is proposed. It is shown that the 1D-RC can properly accommodate ignition, back-supported premixed flame propagation, and diffusion flame. A comprehensive assessment is carried out to validate the efficiency and accuracy of the new FGM tabulation method by using an apriori test using direct numerical simulation (DNS) data and comparing FGM-based DNS with the original DNS results obtained utilizing a detailed chemical kinetic mechanism. It is found that the FGM model can accurately capture not only the overall combustion process but also the fine reaction zone structures and multiple combustion modes. The FGM-DNS is 160 times faster than the full DNS coupling with a detailed chemical kinetic mechanism.