The Effect of Lewis Number on Radiative Extinction and Flamelet Modeling

摘要

The effect of Lewis number on radiative extinction and flamelet modeling is numerically investigated in this study. To highlight the effect of radiation on extinction, flames at low strain rates are considered. The results show that at large Lewis numbers, flames are relatively "weak" and become susceptible to radiative heat losses. With an increase of Lewis number, radiative extinction limit, which has been reported in recent studies to occur at low strain rates, is found to be pushed toward higher values of strain rates. The study also examines the influence of Lewis number and its interaction with transient effects on flamelet combustion modeling. Transient effects are simulated by considering flames subjected to fluctuating reactant concentrations, fluctuating reactant temperatures,a nd variable partial premixing. Based on the flame temperature response, the results indicate that flames subjected to fluctuating reactant concentrations are not much affected by Lewis number. However, a large Lewis number may cause extinction for flames subjected to time dependent concentration fluctuations at high strain rates. The response of flames subjected to variable reactant temperatures or partial premixing is found to increase with an increase of Lewis number.