Experimental and Kinetic Modeling Study on the Autoignition of Ammonia/Propane Mixtures

Utilizing ammonia (NH3) as a zero-carbon alternative fuel requires a deeper understanding of its combustion characteristics, with ignition delay time (IDT) serving as a critical descriptive parameter. To investigate the effects of propane (C3H8) addition on NH3 ignition at high temperatures, the ignition delay times of NH3/C3H8 blends were systematically measured using a shock tube over a wide range of conditions: temperatures of 1263–2117 K, pressures of 0.14–0.5 MPa, equivalence ratios of 0.5–2.0 and propane mole fractions of 5–70%. The results indicate that propane addition significantly promotes ammonia ignition. Under stoichiometric and 1.4 atm pressure conditions, the addition of C3H8 to pure NH3 reduces the ignition delay time by approximately fivefold, allowing auto-ignition to occur at a lower temperature. Furthermore, detailed chemical kinetic mechanisms from the literature were adopted for numerical simulations and validated against the newly acquired experimental data. Kinetic analysis reveals that the propane addition does not alter the main oxidation pathways of ammonia, while it triggers C-N cross-reactions at higher blending ratios (>30%). The active radicals generated during the early stages of propane oxidation accelerate H-abstraction reactions, serving as the key mechanism responsible for the shortened ignition delay times and promoted ignition.