Chemical kinetics of Lean − Rich − Lean fuel-air staged NH3/H2-air combustion for emission control

• Effect of combined fuel–air staging on NOx emissions from NH 3 /H 2 -air combustion is studied. • Implementation of a two-stage ignition pattern of NH 3 /H 2 blends combustion in series is proposed. • Chemical kinetics of lean-rich-lean combustion shows the NO X advantage over traditional rich-lean combustion. • Lean-rich-lean technique integrated with SCR is anticipated to provide low NO X emissions for industrial applications. Ammonia has garnered considerable attention among researchers as a carbon–neutral fuel option. Addressing the challenge of its inherently slow combustion kinetics, significant research efforts have been directed toward mitigating NOx emissions, which represents a critical hurdle in advancing the commercial viability of ammonia as a sustainable fuel. The rich-lean combustion approach has been advocated and demonstrated as the primary means to keep NO X within acceptable emission limits. However, in the current study, a distributed fuel and air injection strategy is proposed and investigated as a superior alternative compared to the traditional rich-lean method for NO X reduction for NH 3 /H 2 -air mixtures with higher ammonia fuel fraction ( X N H 3 = 50 − 90 %). The proposed lean-rich-lean strategy with multi-staging of fuel and air supply is achieved by injecting NH 3 -air mixtures into H 2 -air combustion products followed by a downstream supply of preheated dilution air. Such an injection strategy manages the surge of NH i and O/H radicals while avoiding local temperature peaks by implementing a two-stage ignition pattern of NH 3 /H 2 blends combustion in series. NO X reductions of approximately 48 % and 7 % for X N H 3 = 50 % and 70 %, respectively, is achieved with the lean-rich-lean combustion strategy compared to the rich-lean strategy over a wide range of global equivalence ratios ( ϕ G = 0.3 to 0.7). The lean-rich-lean combustion strategy for atmospheric NH 3 /H 2 -air swirl flames, when integrated with advanced SCR technology, is anticipated to demonstrate a viable approach to achieving zero carbon and low NO X emissions in industrial applications.