Recent advancements in flameless combustion in gas turbines and furnaces using hydrogen, ammonia, and their blends

This is the authors' abstract. We don't add key points for this paper.

Decarbonization requires adopting carbon-free fuels such as hydrogen (H 2 ) and ammonia (NH 3 ). While H 2 offers high reactivity, conventional combustion faces flashback risks and produces excessive thermal NO x emissions due to high flame temperatures. Conversely, NH 3 provides higher volumetric energy density but is hampered by low laminar flame speeds and significant fuel NO x production. This review examines Moderate or Intense Low-Oxygen Dilution (MILD) combustion as a strategy for low-emission combustion of H 2 , NH 3 , and their blends. By leveraging strong internal recirculation, MILD combustion creates a distributed reaction zone that decouples heat release from peak temperatures. Reported pure-H 2 MILD configurations achieve thermal NO x levels below 10 ppm under conditions that maintain high dilution and delayed ignition. For NH 3 , MILD combustion widens the flammability limits, yet emissions management presents a critical trade-off: lean conditions generate fuel NO x , while rich conditions risk NH 3 slip. Reported low-emission operating windows for H 2 -NH 3 blends generally occur near stoichiometric or slightly rich conditions, though the optimum depends on the configuration and operating conditions. H 2 addition can enhance flame stability and shorten ignition delay, but it may also increase NO x emissions, depending on the fuel composition, combustor configuration, and operating conditions. Overall, the reviewed evidence indicates that MILD combustion can contribute to fuel-flexible, low-emission operations, though pressure, scale-up, and stability constraints remain significant barriers.