Experimental Observation Of Ammonia Blending And Cracking On Lean Blow-Out Behaviors In A Model Gas Turbine Combustor

Ammonia is gaining attention as a carbon-free fuel for internal combustion engines in the context of global decarbonization efforts. However, its low reactivity poses challenges for stable combustion. This study investigates two strategies to enhance ammonia combustion: blending it with hydrocarbon fuels (methane) and partially cracking it to produce a hydrogen/nitrogen mixture. A model gas turbine combustor with optical access has been developed to investigate lean blow-out (LBO) behaviors. Experimental results show significantly different LBO behaviors between pure methane and ammonia, a factor of 7 difference in global equivalence ratio. Ammonia blending with methane renders an increase of effective flame volume, thus suppressing overall reactivity, consequently resulting in the increased global equivalence ratio at LBO. Similar LBO behaviors are observed for ammonia cracking simulated by blending ammonia with hydrogen/nitrogen mixture, exhibiting hindered operability by reducing ammonia cracking fraction. The experimental results suggest that a comparable LBO behavior to pure methane can be achieved by cracking 25-30% of ammonia. To further characterize the flame stabilization modes associated with flow recirculation zone, high-speed imaging with power spectral density analysis is employed. Two distinct flame stabilizations modes are observed for ammonia cracking with flame anchoring in the outer recirculation or the inner recirculation zones. The LBO behaviors and the transition of flame stabilization are characterized through scaling analysis by considering the mass flow rates of fuel and air, laminar flame speed, and a representative rotational velocity in recirculation zone or mean fuel jet velocity.