Combustion Chemistry of NH3/CH3OH/H2 Blends

This work aims to study the impact of H2 and CH3OH on NH3 conversion over a wide range of operating conditions, focusing on the influence of temperature, oxygen excess ratio (λ), NH3/H2 (α), and NH3/CH3OH (β). Experiments are conducted in a quartz flow reactor at atmospheric pressure, and outlet species are quantified using a micro gas chromatograph and continuous gas analyzers. NH3 oxidation shows strong sensitivity to both oxygen concentration and fuel mixture ratio. For λ ≤ 1, NH3 conversion is significantly inhibited when CH3OH is present at concentrations comparable to that of NH3 (β ≥ 1). High H2 concentrations promote recycling of NH2 radicals back to NH3, while CH3OH inhibits NH3 oxidation through interactions with NH2, additional H2 formation, and competition for the radical pool. Under fuel-lean conditions, higher OH concentrations mitigate these effects and shift NH3 oxidation to lower temperatures. CH3OH oxidation is dominated by hydrogen abstraction, mainly producing CH2OH radicals, and its inhibitory effect decreases as the NH3/CH3OH ratio increases (β > 1). H2 exhibits a dual role, contributing to the radical pool and promoting oxidation, while inhibiting NH3 conversion at high concentrations through NH2 recycling back to NH3. This effect also decreases under fuel-lean conditions. Overall, NH3 oxidation follows highly branched pathways strongly governed by oxygen availability, whereas CH3OH and H2 exhibit simpler pathways that are less dependent on O2.