Effects of hydrogen and carbon dioxide on the laminar burning velocities of methane-air mixtures

The effects of different mole fractions of hydrogen and carbon dioxide on the combustion characteristics of a premixed methane-air mixture are experimentally and numerically investigated. The laminar burning velocity of hydrogen-methane-carbon dioxide-air mixture was measured using the spherically expanding flame method at the initial temperature and pressure of 283 K and 0.1 MPa, respectively. Additionally, numerical analysis is conducted under steady 1D laminar flow conditions to investigate the adiabatic flame temperature, dominant elementary reactions, and NO formation. The measured velocities correspond with those estimated numerically. The results show that increasing the carbon dioxide mole fraction decreases the laminar burning velocity, attributed to the carbon dioxide dilution, which decreases the thermal diffusivity and flame temperature. Conversely, the velocity increases with the thermal diffusivity as the hydrogen mole fraction increases. Moreover, the hydrogen addition leads to chain-branching reactions that produce active H, O, and OH radicals via the oxidation of hydrocarbons, which is the rate-determining reaction. Furthermore, an increase in the mole fractions of hydrogen and carbon dioxide decreases the NO production amount.