Numerical investigation of the effects of turbulence on the ignition process in a turbulent MILD flame

In this study,we conduct three-dimensional nonlinear large-eddy simulation to investigate the interaction between turbulence and reaction during the initial ignition process of a turbulent methane/hydrogen jet-in-hot-coflow flame under moderate or intense low-oxygen dilution(MILD)condition.Special focus has been placed on the spatial development of the flame and the temporal evolution of representative ignition spots that characterize the range of ignition behaviors observed in the case.Results show that the ignition process of the flame consists of four consecutive phases.Ignition occurs initially with relatively lean mixtures,and compared to the corresponding homogeneous stagnant adiabatic combustion,the loss of radical species associated with flow transportation causes a delay in ignition.The initial ignition spots formed during the autoignition phase provide sufficient conditions for the stabilization of the flame,including the provision of a variety of key radicals.Results also show that the flow convection accompanying the hot coflow dominated the slow flame propagation,and the turbulent mixing is of great importance for rapid flame propagation.These findings will broaden our knowledge of MILD combustion and provide useful insights into advanced ignition contr.