Influence of turbulence–kernel interactions on flame development in lean methane/air mixtures under natural gas-fueled engine conditions

Direct numerical simulations (DNS) with reduced chemistry are carried out to study the influence of flow velocity and length scales on flames developing from flame kernels in lean methane/air mixtures. This study is conducted at elevated temperature and pressure conditions relevant to lean-burn natural gas engines. There are two effects which come into consideration: the interaction of turbulence with the kernel and the interaction with the local flame. A range of scales is selected so that interactions in different regimes can be studied. A flame surface density (FSD) approach is used to determine the evolution of flame area and study how the length and velocity scales enhance or diminish flame development. From the perspective of engine performance, it is observed that shorter length scales lead to faster growth of flame kernels. The ratio of kernel diameter to length scale ratio is identified as an independent controlling variable and its effect is studied by varying the initial size of the flame kernel. Smaller ratios result in a faster increase in the flame area. It is also observed that larger velocity scales lead to higher rates of heat release.