Methodology for Unsteady Exhaust Emissions Characterization in High-Pressure Hydrogen–Ammonia–Methane Flames

A methodology for measuring and interpreting the influence of fuel composition on exhaust emissions in a high-pressure combustor operated with ammonia, methane and hydrogen fuels is investigated. A 19-element micro-mix multi-stage injector is used to introduce the fuel blend premixed with dry, heated air into an optically accessible combustor operating at 10 bar. In such systems, increasing ammonia concentration in the fuel blend can reduce combustion efficiency relative to equilibrium predictions, due to reduced kinetic rates and a corresponding decrease in Damköhler number when the ammonia fuel mole fraction exceeds 75\%. Accurate exhaust-gas composition is required to relate NO\textsubscript{x} formation to combustion efficiency and fuel-bound nitrogen pathways, making extractive gas measurements essential. In short-duration tests, chemical evolution in the sampling hardware, together with thermal and timing constraints on the sampling system, complicate the interpretation of measured exhaust composition as representative of combustor-exit conditions. To address this, an extractive, unsteady sampling approach is combined with a reactor-network model of the gas path from the flame to a heated sampling cylinder and subsequent infrared absorption measurement for species concentrations. This coupled experimental–computational framework is used to investigate how fuel composition, residence time, and heat loss affect inferred NO\textsubscript{x} emissions in hydrogen–ammonia–methane blends, and to identify conditions under which short-duration tests can yield representative exhaust characterization.