The blow-off and transient characteristics of co-firing ammonia/methane fuels in a swirl combustor

Recent studies have demonstrated that ammonia could be one of the most promising hydrogen carrier candidates which can be used in large-scale power plants. However, it is challenging to burn ammonia in gas turbines due to its narrow flame stabilization limits. This study investigates the blow-off characteristics and flame macrostructure transition behavior of ammonia/air flame (i.e. NH 3 flame) and ammonia/methane/air flame (i.e. 50%NH 3 flame) in a swirl combustor. Methane/air flame (i.e. CH 4 flame) is also demonstrated for comparative purposes. The flow field and instantaneous OH profile are measured with PIV and OH-PLIF technique, respectively. Large eddy simulation (LES) is conducted to extend understandings of the experimental findings. The results show that the NH 3 flame possesses a poor lean flame stability limit which can be largely extended by adding CH 4 in the fuel. Moreover, changing swirl number ( S ) shows no apparent effect on the lean blow-off limit ( ?b ) for the NH 3 flame. On the contrary, a clear extension on ?b is found for the 50%NH 3 flame when increasing S . Four flame macrostructure modes can be identified when decreasing equivalence ratio ( ?). The transition from flame II to flame III ( ?t describes the transition equivalence ratio) can be considered as the early warning of blow-off for a swirl stabilized flame. It is found that for the NH 3 flame, there is no clear flame macrostructure transition at small inlet velocities ( U < 3.8 m/s), i.e., ?b ? ?t , while the difference between ?b and ?t will be observed as the inlet velocity increases. However, for the 50%NH 3 and CH 4 flames, a clear flame macrostructure transition from flame II to flame III is observed even for a lower inlet velocity. The LES results show that the NH 3 flame has a faster blow-off process compared to the CH 4 flame, which is mainly attributed to the excessive stretch causing local extinction during the blow-off process. ? 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.