Large eddy simulation of auto-ignition kernel development of transient methane jet in hot co-flow

The auto-ignition process of a transient methane jet issuing into hot co-flow is studied by Large Eddy Simulation (LES). The LES predictions show reasonable agreement with experimental results. A temporal analysis of the transient auto-ignition process is performed, which indicates that the transient auto-ignition process can be divided into four stages in terms of time sequence. The auto-ignition kernel of different times is also analyzed by using Auto-ignition Index, Premixedness Index, and Damköhler number. It reveals that the high temperature region and high release rate region are always located in the flame propagation region and the iso-line of most reactive mixture fraction moves towards the auto-ignition region with the development of auto-ignition kernel. The premixed combustion mainly occurs in the flame propagation region, while premixed combustion and diffusion combustion coexist in the auto-ignition region. At the beginning of the auto-ignition, the Da number of the auto-ignition region is larger than those of the flame propagation region. With the development of the auto-ignition, the Da number of the flame propagation region increases, and larger than the Da number of the auto-ignition region.