H-atoms play a dominate role in hydrogen (H2) and hydrocarbon (HC) combustion chemical kinetics through the chain branching step H + O2 > OH + O whose rate strongly dictates flame speeds and overall fuel/air reaction rates. Accurate prediction of H-atom transport is essential to give accurate flame properties for combustion of H2, HC fuels as well as bio-fuels. However, great uncertainties in the prediction of H-atom transport remain. More accurate H-atom transport models have been proposed but are seldom implemented and have not been validated by flame structure measurements. There are few quantitative H-atom measurements in flames under realistic combustion conditions. H-atom transport is particularly important in stretched and curved flames where preferential diffusion of the H atoms (and other light gases such as H2) is very strong and greatly affects flame temperature, extinction limits and the on-set of cellular flame formation. Highly curved and stretched flame cells can survive beyond normal 1D extinction limits and fast diffusion of H-atoms is essential to the flame survival. The tubular burner creates a highly curved and stretched flame that is ideal for the study of H-atom transport that will lead to advanced and validated molecular transport models. Premixed and non-premixed flames can be studied under uniform stretch and curvature where the overall stretch and curvature can be varied independently. At high stretch and curvature, preferential diffusion of H-atoms will be the strongest and the H-atom distributions can be measured in Vanderbilt's optically accessible burner with H-atom LIF. Stretched cellular flames can be studied with high local curvature that enhances H-atom preferential diffusion. The flame cells formed at extreme conditions in the tubular burner can be measured with H-atom LIF and Raman scattering and the data compared to detailed 3D CFD models with advanced H-atom molecular transport.
Intellectual Merit: In this proposal, we will validate advanced H-atom (and small, light-weight molecule) transport models in H2-fueled tubular flames. H-atom profiles will be measured in hydrogen-fueled non-premixed and premixed tubular flames to validate advanced molecular transport codes. Quantitative 2-photon LIF measurements of H-atoms will be developed using a Raman-shifted ArF laser. The H-atom LIF quenching will be corrected from H-atom LIF measurements in a Hencken burner that are correlated to Raman measurements of flame bath gases in the tubular burner. OH concentrations will be determined with OH LIF signals that are quenching corrected with Raman scattering. The H/OH radical ratio (found to be very sensitive to H atom transport) will be compared between experiment and model to validate the advanced molecular transport code. Accurate H-atom molecular transport models will be implemented into 1D and 3D simulations by Dr. Peiyong Wang at Xiamen University in China. Cellular and non-cellular tubular flames will be studied to validate accurate H-atom transport in a variety of environments. The ultimate outcome will be an advanced validated molecular transport code that can be used in a wide variety of combustion devices (gas turbines, boilers, engines) burning H2, HC and bio-fuels to improve reliability, safety and efficiency.
Broader Impacts: Graduate and undergraduate students including underrepresented minorities will be exposed to the latest computer simulation and laser diagnostic facilities. Engineers will mentor local high school students in engineering design projects and research. Students from Xiamen University and Vanderbilt University will be exchanged to gain global research experiences in experimental and computational combustion and promote Asian-US interactions. Local Nashville high school teachers will be involved in laser diagnostic and combustion research in the summer under the Research Experience for Teachers Program at Vanderbilt University.