Numerical Studies of the Response of Flamelets to Unsteadiness in the Near-Field of Jets Under Diesel Conditions

• Published in: Combustion science and technology 2010-06, Vol.182 (7), p.717-738
• Main Authors: Venugopal, Rishikesh, Abraham, John
• Format: Article
• Language: English
• Subjects: Applied sciences; Combustion. Flame; Diesel fuels; Diesel jets; Energy; Energy dissipation; Energy. Thermal use of fuels; Exact sciences and technology; Extinction/reignition; Jet engines; Laminar flamelets; Oxidation; Pressure; Reynolds number; Temperature; Theoretical studies. Data and constants. Metering; Turbulence models; Unsteady effects
• ISSN: 0010-2202; 1563-521X
• DOI: 10.1080/00102200903415761

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 χ are more suitable for representing the physics.