A Detailed Species Transport Formulation for Flamelet Models of Hydrogen Diffusion Flames.

Abstract: Accurately modeling the turbulence-chemistry interactions in hydrogen diffusion flames is a challenging task due to the unique properties of hydrogen, such as high flame speed and high mass diffusivity. The high mass diffusivity leads to significant differential diffusion effects, such as flame temperatures that exceed the equilibrium temperature. In this work, one-dimensional analysis is performed using an opposed flow flame configuration with the OPPDIFF solver within the CHEMKIN framework. Hydrogen/air diffusion flames at several strain conditions are studied using different species transport methodologies: 1) a full multi-component detailed approach, 2) mixture-averaged, and 3) a unity Lewis number assumption. The predictions are then compared with experimental data. The comparison shows that the detailed and mixture-averaged approaches closely match the experiments in predicting the flame structure, while the unity Lewis number assumption leads to large variations, especially in the predicted peak flame temperature. Finally, the conservativeness of the Bilger mixture fraction is explored for cases that account for detailed transport. The findings suggest that although the Bilger mixture fraction can account for differential diffusion effects, formulating a conserved scalar transport equation for it is challenging. Keywords: hydrogen diffusion flames, differential diffusion, reacting flows, detailed transport, flamelet model