Direct numerical simulation of a turbulent nonpremixed "cool" flame

The low-temperature chemistry characteristics of many fuels can couple with molecular transport to result in low-temperature nonpremixed "cool" flames, that is, thin reacting structures governed by low-temperature chemistry rather than high-temperature flame chemistry. Laminar "cool" flames have been studied both experimentally and computationally, but turbulent "cool" flames have not yet been investigated. In this work, an isolated turbulent nonpremixed "cool" flame of n-heptane and oxygen in isotropic turbulence is simulated using Direct Numerical Simulation. The n-heptane chemistry is described with a skeletal mechanism including low-temperature chemistry, which reproduces both the "cool" and "hot" flames when compared to the detailed mechanism. The results of the DNS calculations indicate that the turbulent nonpremixed "cool" flame is well described by the steady flamelet model when subjected to sufficiently slow turbulence.