End-gas autoignition and knocking combustion of ammonia/hydrogen/air mixtures in a confined reactor

摘要

End-gas autoignition and detonation development in ammonia/hydrogen/air mixtures in a confined reactor is studied through detailed numerical simulations, to understand the knocking characteristics under IC engine relevant conditions. One-dimensional planar confined chamber filled with ammonia/hydrogen/air mixtures is considered. Various initial end-gas temperature and hydrogen concentration in the binary fuels are considered. Homogeneous ignition of stochiometric ammonia/hydrogen/air mixtures is firstly calculated. It is found that H-2 addition significantly promotes autoignition, even if the amount of addition is small. For ammonia/air mixtures and ammonia/hydrogen/air mixtures with low hydrogen mole ratios, it is found from chemical explosive mode analysis results that NH2 and H2NO are most important nitrogen-containing species, and R49 (NH2- +NO=N-2+H2O) is a crucial reaction during thermal runaway process. When the hydrogen mole ratio is high, the nitrogen-containing species and reactions on chemical explosive mode becomes less important. Moreover, a series of one-dimensional simula- tions are carried out. Three end-gas autoignition and combustion modes are observed, which includes forcibly ignited flame propagation, autoignition (no detonation), and developing detonation. These modes are identified within wide ranges of hydrogen contents and initial end-gas temperatures. Furthermore, chemical kinetics at the reaction front and autoignition initiation locations are also studied with chemical explosive mode analysis. Finally, different thermochemical conditions on knocking intensity and timing are investigated. It is found that a higher initial temperature or a higher H-2 content does not always lead to a higher knocking intensity, and the knocking timing decreases with the reactivity of end-gas. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.