Structure and extinction of unsteady, counterflowing, strained, non-premixed flames

✍ Scribed by Fokion N. Egolfopoulos

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 251 KB
• Volume: 24
• Category: Article
• ISSN: 0363-907X
• DOI: 10.1002/1099-114x(200009)24:11<989::aid-er645>3.0.co;2-l

✦ Synopsis

This paper reports numerical investigations on the e!ects of #ow"eld unsteadiness on the structure and extinction of strained laminar non-premixed #ames. The unsteady conservation equations of mass, momentum, energy and species were solved along the stagnation streamline of an opposed jet counter#ow within a "nite domain, including detailed descriptions of the chemistry and molecular transport. The unsteadiness was introduced by imposing sinusoidal variations of the reactant velocity, concentration, and temperature at the exit of the nozzles. The results demonstrate that at low frequencies the #ame structure reacts to the imposed oscillations in a quasi-steady manner, while, at high frequencies, transient e!ects that result in reduced #ame response must be accounted for. It was also found that even though the #ame response is diminished at high frequencies, there is still a substantial transient e!ect felt far from the #ame at the interface between the hydrodynamic and the main di!usive zones that appears to accumulate mass and distort the #uid mechanics before the #ame zone. These phenomena were physically explained from "rst principles. The e!ect of unsteadiness on extinction was also assessed, and the phenomena of partial extinction and re-ignition, extinction delay and extinction suppression were identi"ed. Detailed analysis showed that these phenomena are being controlled by the relative magnitudes of the time scales of the imposed oscillations and the time required for permanent extinction. The results of this analysis are of particular importance to the formulation of laminar #amelet libraries that are needed for the realistic modelling of large-scale combustion devices.