1. Auto-ignition characteristics and chemical reaction mechanism of ammonia/n-heptane mixtures with low n-heptane content.
- Author
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Song, Meijia, Wang, Qiukai, Wang, Zixin, Fang, Yuan, Qu, Wenjing, Gong, Zhen, and Feng, Liyan
- Subjects
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DIESEL motors , *CHEMICAL reactions , *HEAT release rates , *COMBUSTION efficiency , *MIXTURES , *COMBUSTION kinetics - Abstract
• 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]
- Published
- 2024
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