Identifying chemical kinetics contributions to unstable behaviors of a methane-burnt combustion system

Abstract

Chemical kinetics plays a dominant role in power generation and gas turbine combustion systems, where many unstable behaviors are observed and investigated. Here, we propose a chemical delay model and apply it in a methane-burnt combustion system. It is revealed that the time delay between the concentration evolution of representative chemical species and unsteady heat release can be on a similar time scale as the limit cycle oscillations observed in an unstable combustor. Further kinetics studies on the heat release and temperature sensitivity found that the major reactions constitute mutually promoting looped kinetics with both exothermic and endothermic reactions. The loop which forms a chain branching cycle plays the role of thermokinetic feedback which is the key driving mechanism for the self-sustained unsteady heat release. Besides, collision regulated well skipping/stabilization switch, and other associated factors such as the type and dilution of bath gas can effectively affect the thermokinetic feedback.