Numerical studies of the response of flamelets to unsteadiness in the near-field of jets under diesel conditions

Abstract

Turbulent time records of scalar dissipation rates are numerically generated in the near-field of a high Reynolds number turbulent jet. The response of one-dimensional unsteady diffusion flamelets to these records were studied under pressure and temperature conditions representative of those in diesel engines. n-Heptane was chosen as the diesel fuel surrogate, its oxidation chemistry modeled by a 1,540-step mechanism comprising 159 species. Unsteadiness in the scalar dissipation rates was observed to impact autoignition, extinction, and reignition in the near-field. Possible linkages between these observations and flame liftoff, as well as its prediction, in diesel engines are discussed. Steady flamelet models were shown to not capture unsteady extinction-reignition events and associated chemical phase-lag effects. Unsteady flamelet-progress variable (UFPV) models in which the progress variable uniquely identifies all the flame states corresponding to a given value of are more suitable for representing the physics. Copyright © Taylor & Francis Group, LLC.