Probing the reactivity of ammonia/C1 mixtures using shock tube coupled with laser absorption spectroscopy

Ignition delay times (IDT) and speciation profiles (NH 3 , NO, and CO) were measured for NH 3 /C 1 fuel blends (NH 3 /CO, NH 3 /CH 4 , NH 3 /CH 3 OH) in a shock tube using laser absorption spectroscopy. Experiments spanned equivalence ratios of 0.5–1.5, 5–20 % C 1 additives, and temperatures of 1477–2236 K at around 2.5 bar. The experimental data were validated against the simulation results from the PTB-NH 3 /C 2 1.1 mechanism, which demonstrated robust performance across all mixtures. Methanol significantly enhances ignition reactivity, resulting in the shortest IDTs among the three C 1 additives. Combining the findings from our prior studies, the IDT reduction order by different hydrocarbons at high temperatures is: C 2 H 5 OH ≈ C 2 H 6 > CH 3 OH > CH 4 > CO, indicating that high temperature favors C 2 compounds. While at intermediate temperatures and high pressures, where the functional groups dominate, the reactivity order is: C 2 H 5 OH > CH 3 OH > C 2 H 6 > CH 4 , as alcohols enhance reactivity stronger than alkanes. Kinetic modeling analysis identified NH 2 as a key intermediate in NH 3 oxidation, following the primary pathway NH 3 → NH 2 → NH → N → NO. For NH 3 /CO, CO contributed to secondary branching intermediates like HNCO through reactions like NH 2 + CO ≤> HNCO + H , influencing nitrogen-carbon interactions. In NH 3 /CH 4 , hydrocarbon oxidation promoted CO and CH 2 O formation, with limited C N cross-reactions. NH 3 /CH 3 OH pathways exhibited unique CH 3 O and CH 2 OH radical dynamics, facilitating prolonged CO formation and unique broader CO peaks under fuel-rich conditions. While the PTB-NH 3 /C 2 1.1 mechanism captured most trends, discrepancies emerged at lower temperatures and fuel-rich conditions, underscoring the need for further improvement in future. Measuring more intermediate species such as N 2 O, NO 2 , and CH 2 O would also benefit model validation.