- Author
- Puri, I. K.
- Title
- Investigtions of Partially Premixed (Double and Triple) Flames. BFRL Fire Research Seminar. VHS Video.
- Coporate
- University of Illinois, Chicago
- Report
- Video, April 13, 1999,
- Keywords
- premixed flames | gravitational effects
- Abstract
- Steady two-dimensional partially-premixed flames (PPFs) established by introducing a rich fuel-air mixture from the inner slot and air from the two outer slots are investigated. The PPFs contain either two (double) or three (triple) reaction zones. A triple flame is a partially premixed flame containing fuel-rich and fuel-lean premixed reaction zones and a nonpremixed reaction zone. The two premixed reaction zones form exterior wings and the nonpremixed reaction zone is established in between these two wings. A double flame contains only the rich premixed and the nonpremixed reaction zones. The nonpremixed reaction zone is established in the region where excess fuel and oxidizer, from the respective rich and lean premixed reaction zones, mix in stoichiometric proportion. PPFs play an important role in the stabilization and liftoff of nonpremixed flames. They are also of fundamental importance in the reignition of turbulent mixtures. Despite their importance, many aspects of PPFs have not been adequately investigated and are, consequently, not clearly understood. We have investigated laminar PPFs that are stabilized on a Wolfhard-Parker slot burner. The velocity field is characterized using laser Doppler velocimetry and particle image velocimetry, the temperature distribution using laser interferometric holography, and the species distributions using gas chromatography. In addition, C2*-chemiluminescence images of the three reaction zones are obtained. Our results focus on the detailed structure, the interaction between the three reaction zones, the dependence of the flame structure on the initial velocities and mixture equivalence ratios and the dominant chemical pathways. The lean premixed reaction zone (external wing) exhibits different features from the rich premixed reaction zone. In particular, it is characterized by strong HO2 formation and consumption reactions, and by relatively weak methane consumption reactions. Radical activity is higher in the nonpremixed reaction zone than in the other reaction zones. Overall, radicals from the nonpremixed reaction zone are transported to both the rich and lean premixed reaction zones where they attack the reactants. Under normal-gravity conditions the flame heat release produces both flow dilatation and buoyancy effects. While it may be possible to minimize gravitational effects in a fully-premixed flame by isolating buoyancy effects to the lower-density post-flame region or plume, this cannot be accomplished in nonpremixed flames. It is known that partially-premixed flames can contain two reaction zones, one with a premixed-like structure and the other consisting of a transport-limited nonpremixed zone (in which mixing and entrainment effects are significant). We have also investigated the interaction between flow dilatation and buoyancy effects in partially-premixed flames.