The Stability and Structure of Lean Hydrogen-Air Flames: Effects of Gravity
Abstract
Detailed, time-dependent, two-dimensional numerical simulations with full hydrogen-oxygen chemistry are used to investigate the effects of gravity on the stability and structure of laminar flames in lean, premixed hydrogen - air mixtures. The calculations show that the effects of gravity becomes more important as the lean flammability limit is approached. In a 12% hydrogen - air mixture, gravity plays only a secondary role in determining the multidimensional structure of the flame with the stability and structure of the flame controlled primarily by the thermo-diffusive instability mechanism. However, in leaner hydrogen-air mixtures gravity becomes more important. Upward-propagating flames are highly curved and evolve into a bubble rising upwards in the tube. Downward- propagating flames are flat or even oscillate between structures with concave and convex curvatures. The zero-gravity flame shows only cellular structures. Cellular structures which are present in zero gravity can be suppressed by the effect of buoyancy for mixtures leaner than 11% hydrogen. These observations are explained on the basis of an interaction between the processes leading to buoyancy-induced Rayleigh-Taylor instability and the thermo-diffusive instability. Effects of gravity, Flame stability, Flame structures.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 17, 1990
- Accession Number
- ADA276399
Entities
People
- G. Patnaik
- Kazhikathra Kailasanath
Organizations
- United States Naval Research Laboratory