Modeling of Structure and NO Formation in an Oscillating Stagnation Flame

Yei-Chin Chao ； Yao-Wei Huang ； Gun-Ban Cheng

《中國航空太空學會學刊》 36卷3期 (2004/09) Pp. 225-231

https://doi.org/10.6124/TAASRC.200409_36(3).04

並列摘要

To further study the unsteady NO formation behavior in the premixed flames, numerical simulation using CHEMKIN packages and GRI Mech. 3.0 is performed on the flat flame in the stagnation flow field subject to unsteady straining induced by periodically changing the flow rate (case 1) and the distance between plate and nozzle exit (case 2). The resultant flame thickness and T(subscript max) show either nearly no response to strain rate variation for high frequency or coincident with the steady curve without significant phase delay for low frequency cases. Unlike the diffusion flames presented by Im et al. (1999), the major axis of the phase-delay oval for the NO concentration in premixed flames does not coincide with the steady curve. The inclined angle between the major axis and the steady curve is larger for the low frequency case. The effect of NO slow reaction becomes significant for low frequency cases. The value of T(subscript max) and relative NO concentration is higher in case 2 than that in case 1. When the distance L is oscillatory (case 2), after a peak response before 90o the normalized T(subscript max) location from the plate, d/L, and the normalized flame thickness, f/L, almost remain constant at 0.2 and 0.52, respectively. The NO formations are dominated by the mechanism of thermal and NNH pathways. The reason is that higher T(subscript max) is obtained in case 2 and therefore, the dominate mechanism in case 2 is thermal, instead of prompt pathway in case 1.

並列關鍵字

Oscillating flames ； Unsteady ； NO emissions ； Flat flame