Impact of Hydrogen Addition to Natural Gas on Combustion Instability

Abstract

The transition to low-carbon energy systems demands cleaner combustion technologies capable of operating efficiently with hydrogen-enriched fuels. However, introducing hydrogen into conventional natural gas systems can significantly alter flame behaviour and potentially compromise combustion stability. This thesis addresses the following research questions: (1) how pressure affects combustion stability in pure hydrogen flames; (2) how hydrogen addition to natural gas influences combustion stability across different operating conditions; and (3) whether low-order acoustic or thermoacoustic models can predict the stability regimes of hydrogen/natural gas flames under gas-turbine-relevant conditions.

To answer these questions, this thesis investigates the impact of hydrogen addition to natural gas on flame dynamics and combustion stability under elevated-pressure conditions relevant to gas turbines. A novel optically accessible burner was developed to enable detailed measurements of flame shape, heat release rate dynamics, and pressure oscillations across a wide range of fuel blends, pressures, and operating conditions. The results show that increasing hydrogen concentration shortens flame length, alters flame–acoustic interactions, and shifts heat release rate spectra to higher frequencies, making high-frequency acoustic modes more prone to instability in hydrogen-rich flames.

Overall, these findings provide new insights into the stability characteristics of hydrogen-containing fuels and demonstrate the capability of low-order models to capture key stability trends, supporting the development of low-emission, hydrogen-fuelled gas turbines.