SIMULATION OF THE BEHAVIOR OF RICH HYDROGEN-AIR FLAMES NEAR THE FLAMMABILITY LIMIT

This paper presents an investigation of the behavior of rich hydrogen- air flames near the flammability limit. Ignition processes are simulat ed using a computational model which involves the solution of the gove rning equations (for one-dimensional geometries) by implicit methods o n an adaptive nonuniform grid, using detailed chemistry and a multi-sp ecies transport model. The reaction mechanism consists of 37 elementar y reactions and 9 species. Calculations have been performed for differ ent one-dimensional geometries. An investigation of the fundamental fl ammability limit (intrinsic to the combustion system itself), which is governed only by the physical and chemical processes in the gaseous m ixture, is carried out by eliminating external factors such as heat lo ss, buoyancy, etc. in the calculations. Computations have been perform ed for hydrogen-air mixtures of varying hydrogen content. Mixtures con taining 75% or less hydrogen are found to be steadily propagating, whe reas mixtures containing 82% or more hydrogen extinguish. Inbetween th ese bounds, an oscillatory flame propagation is observed, which is cha racterized by an oscillation between a fast and a slow flame propagati on. Furthermore, the effect of the pressure on the flammability limit is studied.