Edinburgh Napier University

  The dominant physical processes that characterize the combustion of a lean methane/air mixture, diluted with exhaust gas recirculation (EGR), under turbulent MILD premixed conditions are identified using the combined approaches of Computational Singular Perturbation (CSP) and Tangential Strech Rate (TSR) which identifies the driving processes of the system dynamics. The important modes that contribute the most to the TSR are identified and the competition between the processes that oppose to or promote the action of each mode is studied. Two important modes are found to compete for the largest part of the domain, one of explosive character and one of dissipative nature. This competition mostly favors the dissipative modes, suggesting that the system’s dynamics is predominantly dominant. It was also found that the key processes that trigger this competition are hydrogen-related reactions introduced by the explosive mode and carbon-related reactions introduced by dissipative modes. Furthermore, it was also found that the chemical activity of the explosive modes is enhanced by transport processes, in particular convective processes, despite their dissipative nature.