A stretched laminar flamelet model of turbulent nonpremixed combustion

✍ Scribed by S.K. Liew; K.N.C. Bray; J.B. Moss

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 835 KB
• Volume: 56
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(84)90037-3

✦ Synopsis

A model is described which permits the incorporation of complex hydrocarbon chemistry into a detailed flow field prediction for turbulent nonpremixed combustion. The microscopic element in the turbulent ensemble is taken to be a stretched laminar flamelet, drawn from a library of such flamelets in which the extent of local stretching is characterized by X =-2l) (d~Jc)xk) (O~JOxk). This quantity, which varies with position in the laminar flamelet, is evaluated at the location of the peak temperature.

The mean turbulent scalar dissipation rate, X, is used, in conjunction with a quenching criterion based on the limiting value ofx for sustained burning, to partition the several contributions to the mean thermochemical state. The quenching limit is determined numerically from the solution of an unsteady, reaction-diffusion balance equation which models realistically the detailed chemistry. With the quenched state modeled as an inert mixing process, predictions are made for open turbulent methane-air flames extensively reported in the literature. While the effects of stretch are relatively small throughout much of the flow field, the significantly diminished probability of local burning in the neighborhood of the limits of the potential core admits significant penetration of oxygen into the flame zone as is observed experimentally. The results have potentially important implications for practical combustors in which mixing will typically be more intense than in open flames.