Characterization of CH4-CO2-O2 diffusion flames near autothermal reforming condition

Autothermal reforming (ATR) of methane is a promising technology for low-carbon H production due to its high CO capture efficiency (>95 %) and cost advantage. Especially, reforming CO+CH greenhouse gases to valuable CO+H gases is a feasible solution for carbon-neutral energy systems. Flame temperature, reforming gas composition and concentration, and soot loading are major factors determining the efficiency of H production in the subsequent catalyst region. In this study, the effects of CO/CH ratio on the profiles of temperature, OH radical, light gas products, large polycyclic aromatic hydrocarbons (PAHs), and soot were investigated for CH-CO-O laminar inverse diffusion flames near ATR conditions, using the combined non-intrusive and intrusive diagnostic methods. Pure O as oxidizer was fed through the central nozzle of the burner surrounded by CH fuel diluted with CO. The experimental results revealed that the formation of soot and PAHs was greatly suppressed with a higher CO/CH ratio. The PAHs and soot loading followed exponential function as CO/CH mole ratio, regardless of pressure, O mole fraction, and burner size. The flame height was found to increase linearly with CO dilution, and the high temperature region (> 1000 K) shifts downstream. The H production decreased with CO/CH ratio, while CO production is less sensitive to CO dilution. The importance of radical species during soot formation is confirmed based on the comprehensive data set. Moreover, five well-known chemical-kinetic mechanisms were evaluated against experimental datasets. The comparisons indicate that the flame temperature and concentration trends of investigated species are well predicted, but future work is needed to improve the prediction accuracy of amplitude and spatial distribution, especially for CH, PAHs and soot. The reported experiment and simulation results can provide valuable guidance for ATR model validation, development, reduction, and application.