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• Auto-ignition properties of ammonia with low n-heptane content were studied using RCM. • The IDTs were measured in the temperature range 620–970 K and pressure range 15–25 bar. • An optimization was conducted based on the existing detailed reaction mechanism. • A small content of n-heptane has a great effect on the IDT and HRR of the mixture. • N-heptane is consumed mainly by the reaction of extracting H atoms by NH2. The low reactivity of ammonia leads to a low combustion efficiency of premixed combustion mode ammonia-diesel engines. In order to overcome this shortcoming, a small amount of diesel is pre-injected into the ammonia pre-mixture to increase the reactivity. Therefore, this study investigated the auto-ignition characteristics of lean-equivalent-rich ammonia/n-heptane mixtures at low n-heptane blending ratios (2 %&5 %&10 %) and wide thermodynamic conditions (Temperature range of 620–970 K, Pressure range of 15–25 bar) via rapid compression machine. The results showed that a small content of n-heptane had a strong ignition-promoting effect: significantly reducing the Ignition Delay Times (IDTs) and increasing the heat release rate. Besides, the IDTs of the mixture decreased with the increase in equivalence ratio, while the stoichiometric mixture showed the highest heat release rate. Moreover, an improved dual-fuel mechanism, which dramatically enhanced the predictive performance of IDTs for ammonia/n-heptane and pure ammonia mixtures, was proposed to illuminate the reaction kinetic properties. N-heptane is consumed prior to ammonia and at a higher rate. The reaction of NH 2 extracting H atoms from n-heptane was the main consumption reaction of n-heptane at low n-heptane content conditions. And the reaction of ammonia consuming OH radicals was the most ignition-inhibiting reaction. Besides, the reaction NH 3 + O 2 = NH 2 + HO 2 plays an important role in the extent of the negative temperature coefficient effect for the mixture under different blending ratios and equivalence ratios. [ABSTRACT FROM AUTHOR]

The development of methanol/diesel dual-fuel engines urgently requires further study on chemical kinetic models for binary fuels. Ignition delay of lean and stoichiometric methanol/n-heptane mixtures (30/70, 50/50, 70/30, and 90/10) diluted with argon was investigated at high temperature (T = 1195 K–1514 K) and low pressure (p = 2 bar) using an aerosol shock tube and a detailed LLNL3.1 mechanism. The results indicated that LLNL3.1 mechanism agreed well with the current measurements. An increase in methanol can accelerate the ignition process at Ф = 1, because of the key radical---HO2, produced by CH2OH + O2=CH2O + HO2, which was affected by the methanol concentration. HO2 would subsequently attack the parent fuels and combine with H radical (HO2+H = 2OH), leading to the booming radical pool. For lean mixtures, n-heptane promoted the reactivity of system due to its high sensitivity to reaction H + O2=O + OH. The higher initial O2 concentration expedited this reaction and shortened the IDT. Besides, both methanol and n-heptane undergo H-abstraction reaction mostly by H radical, however, these reactions showed an inhibition effect on reactivity. This is caused by the competition for H radical between O2 and the parent fuels. Also, the fuel radicals, produced by C7H15-3, had a low decomposition reaction rate thus slowing down the chain branching and suppressing the reactivity of system. • Ignition characteristics of methanol/n-heptane mixtures were studied by shock tube and mechanism. • Methanol accelerated the auto-ignition for stoichiometric mixtures due to the HO2 radical. • N-heptane promoted the reactivity for lean mixtures due to its high O2 sensitivity. • H-abstraction of the parent fuels by H radical showed an inhibition on auto-ignition. [ABSTRACT FROM AUTHOR]