Parametric evaluation of the operating conditions for NO reduction in flameless combustion of an H2/NH3/N2 fuel mixture

The transition from hydrocarbon-based to carbon-free fuels is imperative owing to environmental concerns and stricter regulations. However, the combustion of hydrogen (H2) and ammonia (NH3) generates nitrogen oxide (NO) and faces operational constraints. Hence, technologies like flameless and moderate or intense low-oxygen dilution combustion are being explored to mitigate NO formation. This study analyzed flameless combustion of H2/NH3/N2 fuel mixture, assessing the impacts of varying fuel velocity, feed strategy, equivalence ratio, and O2 content on NO emissions. Using a laboratory-scale combustor, flameless combustion was achieved via controlled flow and internal recirculation. Lower fuel velocity improved combustor temperature uniformity and reduced NO emissions. Feeding NH3 separately decreased NO emissions compared to mixing it with fuel. Decreasing excess O2 enhanced temperature uniformity, suppressed fuel-NO formation, and reduced NO emissions. N2 dilution improved fuel-oxidizer mixing, enhancing temperature uniformity and reducing NO emissions, highlighting how parameter optimization enhances temperature uniformity and lowers NO emissions.