  The addition of hydrogen in ammonia/air mixtures can lead to the onset of
intrinsic flame instabilities at conditions of technical relevance. The length
and time scales of intrinsic instabilities can be estimated by means of linear
stability analysis of planar premixed flames by evaluating the dispersion
relation. In this work, we perform such linear stability analysis for
hydrogen-enriched ammonia/air flames (50%H2-50%NH3 by volume) using direct
numerical simulation with a detailed chemical kinetic mechanism. The impact of
pressure and the inclusion of the Soret effect in the governing equations is
assessed by comparing the resulting dispersion relation at atmospheric pressure
and 10 atm. Our data indicate that both pressure and the Soret effects promote
the onset of intrinsic instabilities. Comparisons with available numerical
literature data as well as theoretical models are also discussed.
