Oxidation of Ammonia Blends with Methyl Formate in a Supercritical Pressure Jet-Stirred Reactor up to 100 atm

Ammonia (NH3) is a carbon-free fuel with strong potential for low-emission combustion systems, but its low reactivity limits practical application. Blending NH3 with oxygenated fuels offers a promising strategy to enhance ignition and oxidation characteristics while influencing NOx formation pathways. In this work, the oxidation of NH3/CH3OCHO(MF)/O2/N2 mixtures is studied in the Princeton supercritical-pressure jet-stirred reactor (SP-JSR) at 100 atm over 350–950 K under fuel-lean and fuel-rich conditions. Quantitative measurements of major species and intermediates are obtained, and a high-pressure kinetic mechanism (HP-Mech) is developed by integrating updated MF oxidation kinetics, NH3 sub-mechanisms, and newly introduced MF/NH3 coupling reactions. The updated mechanism accurately captures NH3 consumption trends and key intermediate profiles, outperforming existing models under ultra-high-pressure conditions. Path-flux analysis shows that MF oxidation is dominated by OH-initiated H-abstraction, while MF/NH3 interactions mainly occur through MF/NO2/NH2 coupling. OH sensitivity analysis at 800 K further confirms the dominant role of CH3OCHO + NO2 in sustaining OH and NOx. Overall, the results provide the first detailed experimental and kinetic study of NH3/MF oxidation at ultra-high pressure and clarify the mechanistic basis for how oxygenated fuels promote or suppress NH3 reactivity, and inform combustion strategies for high-efficiency, low-carbon engine systems.