Exergy destruction behavior of chemical reactions during the auto-ignition of methane doped with hydrogen

Abstract

Chemical reaction is the major source of combustion irreversibility in premixed conditions, and revealing the details of exergy destruction can provide a more essential perspective on exploring high-efficiency combustion strategies. The present study focuses on the homogeneous combustion process of CH4/H2/air mixtures, aiming to reveal the exergy destruction behavior of chemical reactions from the viewpoint of different combustion stages and oxidation paths. Results indicate that exergy destruction is mainly accumulated in the ignition delay stage, and the exergy destruction caused by different elementary reactions depends on the temperature at which the reaction takes place and the resulting change of free energy. By dividing the chemical reactions into four groups, the main reaction channels that contribute to the change in exergy destruction with combustion boundaries have been identified. Global reaction flux analysis reveals the effect mechanism of different oxidation paths on exergy destruction. Furthermore, the staged combustion concept with endothermic reactions reacting firstly at lower temperatures followed by dilute combustion in the high-temperature heat release stage is discussed from the point of the exergy destruction evolution, which offers the potential to simultaneously reduce exergy destruction and suppress NOx formation.