A direct comparison of pair-exchange and IEM models in premixed combustion

✍ Scribed by Sanjay M. Correa

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 867 KB
• Volume: 103
• Category: Article
• ISSN: 0010-2180
• DOI: 10.1016/0010-2180(95)00096-o

✦ Synopsis

Two pair-exchange mixing models, viz., the original Curl model and a modification thereof, are compared with the "Interaction-by-Exchange-with-the-Mean" (IEM) model, in the context of homogeneous combustion. The IEM model is attractive because it permits highly "parallelizable" computation, but the consequences of certain peculiarities--such as determinism and the shape-preserving relaxation of the initial pdf of a conserved scalar---need to be examined in the context of combustion. A numerical simulation of a partially stirred reactor (PaSR) is used to directly compare the three models, without the additional errors that contaminate comparisons made in simulations of fiowfields. The fuel is 50%CO/50%H 2 (by vol.). The kinetic scheme consists of 11 species and 23 reactions. The stoichiometry of the premixed inflow leads to a PSR temperature of 1740 K, but to blowout in a PFR. The PaSR mixing frequency was varied in the range l0 Hz to 104 Hz, by factors of 1~. The pair-exchange models predict blowout earlier than does the IEM model. Means computed from the IEM model are less noisy, a consequence of the determinism inherent in the IEM model. Despite these differences, the pdfs and scatterplots of temperature, CO, OH, and O--selected because of their intrinsic importance as well as their influence on NO x emissions--are very similar between the three models. The similarity increases with the mixing frequency, which is significant given that practical (e.g., gas-turbine) combustors operate at high mass-loadings and therefore necessarily at high mixing rates.