Direct Numerical Simulation of the Transition from a Laminar Cool n-Heptane/Air Ignition Front to a Distributed Premixed Turbulent Cool Flame

摘要

The first direct numerical simulation of a 3D n-heptane/air premixed turbulent cool flame in turbulence intensity typical of the thin reaction zones regime is presented. Chemistry is described by a 129-species, 1234-reaction mechanism (reduced from CaltechMech). Under the current conditions (1 atm, 650 K, and equivalence ratio of 0.7) the initial laminar cool flame is strongly affected by auto-ignition, which is expected to occur under engine conditions, and has an ignition front (or wave) structure. As the turbulent flame develops, turbulent diffusion becomes sufficiently large to initiate self-propagation of the cool flame. The flame is observed to propagate upstream steadily until it reaches the inlet. The steady-state turbulent flame is found to be highly distorted and have a highly distributed reaction zone. As a result, the chemical source terms and heat release rate conditioned on temperature are strongly reduced (more than 50%) compared to the reference laminar cool flame. However, this strong turbulence does not affect the global chemical pathways, but only their magnitude and locations in temperature space.