Intrinsic combustion instabilities in ammonia-hydrogen/methane non-premixed flames

Intrinsic combustion instabilities that onset in NH 3 -H 2 and NH 3 -CH 4 non-premixed flames are experimentally characterized. A unique research burner capable of creating a good approximation of the classical onedimensional chambered non-premixed configuration is used, enabling direct comparison with theoretical stability models based on this simple configuration. Starting from a stable flame near the Burke-Schumann limit, the Damk & ouml;hler number is gradually reduced by decreasing the fuel concentration, going through the marginal stability state where instabilities onset. Both CO 2 and N 2 dilution are considered, and global stability limits are provided for a wide range of fuel blends. The instabilities are diffusive-thermal in nature, where it is shown that unstable NH 3 -CH 4 flames exhibit pulsations in their reaction rates due to their large Lewis numbers. The characteristic pulsation frequency is highly dependent on the NH 3 fraction in the fuel. A peculiar phenomenon is reported when H 2 with a small Lewis number is added to the less mobile NH 3 species. Superimposed cellular-pulsating instabilities form in NH 3 -H 2 flames, which are thoroughly characterized as a function of the NH 3 fraction.