Premixed flame behaviors of H2/CH4/C3H8 mixtures in a narrow-gap disk burner and effective Lewis numbers

Abstract

Hydrogen combustion is receiving significant interest as a carbon-free energy resource. However, the distinctive combustion characteristics of hydrogen have yet to be explored sufficiently. This study experimentally investigated the effects of hydrogen blending with methane and propane using a narrow-gap disk burner (NGDB). Three representative flame characteristics were considered: the quenching distance, the flame propagation velocity, and the number of cellular structures. It was confirmed that the quenching Peclet number and the number of cellular structures were significantly affected by the addition of hydrogen, primarily due to the Lewis number. However, defining the Lewis number was somewhat ambiguous, especially for multi-component fuel mixtures. Although various effective Lewis numbers have been suggested, their reliability must be adequately assessed. Six representative Lewis numbers were evaluated based on previous studies, and their correlations with flame characteristics were discussed. Conclusively, the previous Lewis numbers were only partly acceptable and had some exceptions. Therefore, a revised effective Lewis number for the hydrogen-blended flames was suggested, using the maximum laminar burning velocity as a new criterion for determining the deficient species, which showed improved correlations with representative flame propagation characteristics.