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 (ln tau ig similar to 1/T) was linear under different equiva-lence 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 re-actions. 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.

Automated summary

This study aims to investigate the influence 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 different conditions. A simplification model (NH3-M model) was constructed based on the Zhang and FFCM-1 mechanisms, and chemical kinetic analyses were performed. The results showed that the addition of 5% methanol significantly shortened the IDTs of the ammonia/methanol mixtures.