Effect of methanol blending on the high-temperature auto-ignition of ammonia: An experimental and modeling study

To explore the effect of methanol addition on the auto-ignition of ammonia under high temperature and low pressure, the ignition delay times (IDTs) of ammonia/methanol mixtures were studied using a shock tube at equivalence ratios of 0.5, 1.0 and 2.0, temperatures of 1250–2150 K and pressures of 0.14 and 1.0 MPa. Based on the coupling of the Zhang and FFCM-1 mechanisms, a combined simplification model (NH3-M model) was constructed using the direct relationship graph method. Chemical kinetic analyses were then performed based on the NH3-M model. The results showed that the addition of 5 % methanol could shorten the IDTs of the ammonia/methanol mixtures by more than 60 %. The correlation between the logarithm of the IDT of the ammonia/methanol mixtures and the reciprocal of ignition temperature (lnτig ∼ 1/T) was linear under different equivalence ratios and pressures. The IDTs of the ammonia/methanol mixtures were mainly affected by small radicals, such as OH, O, HO2 and H. The initial consumption of ammonia and methanol began with H-abstraction reactions. Furthermore, it was not R466 (CH3OH + NH2 = NH3 + CH3O) and R467 (CH3OH + NH2 = NH3 + CH2OH) that directly promoted ignition but the active substances generated from the intermediates produced by R466 and R467 that facilitated the entire reactions.