This program will provide a library of strained flamelet structures for hydrogen-air turbulent combustion modeling. Spontaneous Raman scattering will be used to obtain temperature and major species concentration profiles in opposed-jet hydrogen-air counterflow diffusion flames at varying fuel dilutions and strain rates. The strain rate will be determined from axial velocity profiles using laser velocimetry. Laser-induced fluorescence will be used to obtain the OH concentration profile which can be related to the extent of local chemical reaction. Flames with strain rates up to extinction will be examined, as will flames with varying amounts of nitrogen diluent added to the fuel. The effects of finite-rate chemistry, preferential diffusion, Lewis Number, and strain rate on opposed jet flames can be discerned from these experimentally measured flame structures. An important modeling effort directed toward the characterization of turbulent combustion is the laminar diffusion flamelet theory, which models turbulent diffusion flames as ensembles of strained laminar diffusion flamelets. This type of combustion model can be used to predict temperature profiles, pollutant production, and liftoff characteristics of turbulent flames, but the laminar flamelet data that are utilized by the model must correctly represent the various fluid dynamical, diffusional, and kinetic effects present. This laminar flamelet information can be in the form of "libraries" of diffusion flamelet structures of the type to be developed in this program. Once the laminar diffusion flamelet library correctly treats the effects listed above, it can be used to more successfully model turbulent hydrogen-air combustion, including the high speed combustion in Scramjet engines.
