Flame stabilization and emission characteristics of ammonia combustion in lab-scale gas turbine combustors: Recent progress and prospects

Global climate change forces all countries to push the process of de-carbonization. Ammonia, which is carbon free and a potential hydrogen carrier, is proposed as a prospective fuel for the power devices to realize the green economy. It also exhibits very good fuel properties, including its storage condition, energy density. However, two main challenges, the difficulties of flame stabilization and potential high fuel NO_x production, still need to be tackled in its application in gas turbines. In the last decades, valuable investigations were conducted to address characteristics of NH₃/air flame stabilization in swirl combustors as well as the combustion enhancement by cofiring with active molecule like CH₄ and H₂, applying plasma assistance. These measures mainly improve the flame resistance to the flow and increase the key radicals at flame base, which may provide possible solutions to the combustion chamber design. The inherent mechanisms of fuel NO_x production are highlighted by the HNO channel with the presence of OH radical. One promising strategy to mitigate NO_x in gas-turbine like combustor is the staged combustion by staging the air or fuel, which may also fit for the practical combustion chamber. The high-pressure condition and plasma assistance were found to show positive influence on both flame stabilization and NO_x control. This review also emphasizes the fundamental research issues for ammonia fuel and proposes some future research prospects towards the development of more robust, reliable, and low NO_x combustion technologies relevant to gas turbines.