Fundamental Combustion Characteristics of Lean and Stoichiometric Hydrogen Laminar Premixed Flames Diluted With Nitrogen or Carbon Dioxide

In this work, the laminar combustion characteristics of H-2/N-2/air (H-2/CO2/air) were systematically investigated under different hydrogen ratios (40-100%) and equivalence ratios (0.4-1.0) in a closed combustion vessel using the spherical expanding flame method associated with Schlieren technology. The unstretched laminar burning velocities were compared with data from previous study, and the result indicates that excellent agreements are obtained. Numerical simulations were also conducted using GRI3.0 and USC II mechanisms to compare with the present experimental results. The Markstein length for H-2/inert gas can be decreased by decreasing the equivalence ratio and hydrogen ratio. The results indicate that the H-2/inert gas premixed flames tend to be more unstable with the decrease of equivalence ratio and hydrogen ratio. For H-2/N-2 mixture, the suppression effect on laminar burning velocity is caused by modified specific heat of mixtures and decreased heat release, which result in a decreased flame temperature. For H-2/CO2 mixture, the carbon dioxide has stronger dilution effect than nitrogen in reducing laminar burning velocity owing to both thermal effect and chemical effect.