A shock-tube study of the co-pyrolysis of ammonia and methane

Ammonia (NH 3 ) is a promising carbon-free fuel; however, its low chemical reactivity and narrow flammability limits hinder its direct application in combustion systems. Blending NH 3 with methane (CH 4 ) enhances reactivity, yet the underlying NH 3 /CH 4 interactions under pyrolysis conditions remain insufficiently validated. The present study investigates the co-pyrolysis of NH 3 /CH 4 in a shock tube by measuring NH 3 time histories using laser absorption spectroscopy near 10.39 μm. The experiments were performed for NH 3 /CH 4 /Ar mixtures over a temperature range of 1812–2804 K and at near-atmospheric pressure. Four mixtures were investigated containing approximately 0.75% NH 3 with CH 4 fractions in the total fuel of 12%, 25%, 40%, and 55%. NH 3 half-life times were extracted from the measured NH 3 profiles and compared with predictions from nine recent kinetic mechanisms, revealing significant discrepancies at low and intermediate temperatures that increase with CH 4 addition. Among the mechanisms considered, the Murakami mechanism provided the best overall agreement and reproduced both NH 3 profiles and the half-life time data across the full range of conditions. Reaction pathway and sensitivity analyses identified CH 2 NH as the pivotal intermediate linking C–N chemistry to HCN formation, while NH 3 + H ⇄ NH 2 + H 2 and CH 3 + H + M ⇄ CH 4 + M (in reverse) were identified as the key reactions controlling NH 3 consumption. The resulting dataset provides novel validation targets for NH 3 /CH 4 kinetics and improves understanding of C–N chemistry under pyrolysis conditions. To the best of our knowledge, this work reports the first shock-tube study on the co-pyrolysis of NH 3 and CH 4 , providing new validation benchmarks for future ammonia/hydrocarbon combustion mechanisms.