Intrinsic instability of lean hydrogen/ammonia premixed flames: Influence of Soret effect and pressure

TL;DR

This study investigates how pressure and the Soret effect influence intrinsic flame instabilities in hydrogen-enriched ammonia/air flames through linear stability analysis and direct numerical simulations.

Contribution

It provides new insights into the combined impact of pressure and Soret effect on flame stability in hydrogen-ammonia mixtures using detailed kinetic modeling.

Findings

Pressure and Soret effect promote intrinsic flame instabilities.

Higher pressure (10 atm) increases instability onset.

Soret effect influences flame stability at different pressures.

Abstract

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.