An experimental and detailed kinetic modeling study of the auto-ignition of NH3/diesel mixtures: Part 1- NH3 substitution ratio from 20% to 90%
An experimental and detailed kinetic modeling study of the auto-ignition of NH3/diesel mixtures: Part 1- NH3 substitution ratio from 20% to 90%
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DOI：
10.1016/j.combustflame.2022.112391
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发表时间：
2022-10
影响因子：
4.4
通讯作者：
Yongxiang Zhang;Wei Zhou;Yueying Liang;Liang Yu;Xingcai Lu
中科院分区：
文献类型：
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作者：
Yongxiang Zhang;Wei Zhou;Yueying Liang;Liang Yu;Xingcai Lu
氨（NH3）作为一种优良的无碳载氢燃料，近年来作为一种很有前途的内燃机替代燃料受到广泛关注。为了探索NH3与柴油混合燃料在内燃机上的应用潜力，在快速压缩机上测定了NH3/柴油混合燃料在20%、40%、60%、70%、80%和90%的宽NH3能量分数，675-995 K，20-50 bar压力下的自燃延迟时间，当量比为0.5-1.5。根据着火延迟期随温度的变化规律，可以确定NH3/柴油混合气的三种不同燃烧状态。研究发现，典型的NTC行为和两阶段着火过程中只观察到的制度，柴油化学占主导地位。第一阶段和总点火延迟时间均随NH3能量分数的增加而增加，随当量比的增加而减小。在此基础上，通过增加柴油与NH3之间的交叉反应，提出了一种更新的NH3/柴油反应机理。结果表明，该机理对NH3含量为20%的混合气的着火延迟时间的预测能力较原机理有明显提高，但仍不能再现NTC范围内的着火延迟时间。进一步的灵敏度分析和OH自由基生成速率分析表明，NTC范围内NH3/柴油混合燃料反应性的高估与反应NO+ HO 2双键NO2 +OH密切相关。NO物种对低温下活性HO 2自由基转化为活性OH自由基的促进作用大大加速了自燃。此外，现有的反应机理没有考虑大的NTC相关物种（QOOH，OOQOOH，OQOOH，ROO）与含氮物种（NO，NO2，NH 2）之间的交叉反应，尤其是NO相关的反应，这可能会对NH3/柴油混合物的IDT模拟产生很大的影响。因此，这项工作提出了新的着火延迟时间的测量和机理优化的NH3/柴油混合物。为了进一步了解NH_3/柴油混合燃料的燃烧行为，需要对这些不清楚的反应进行进一步的研究。
Ammonia (NH3) is considered as a good carbon-free hydrogen-carrier fuel and has gained extensive attention as a promising alternative fuel for internal combustion engine in recent years. To explore the application potential of the NH3burned with diesel fuel in internal combustion engine, the auto-ignition delay times of NH3/diesel fuel blends were measured in a rapid compression machine at a wide NH3energy fraction of 20%, 40%, 60%, 70%, 80%, and 90%, temperature range of 675–995 K, pressures of 20–50 bar, and equivalence ratios of 0.5–1.5. According to the variation of ignition delay times with temperature, three different combustion regimes for NH3/diesel mixtures can be determined. It is found that the typical NTC behavior and two-stage ignition process were only observed at the regime where diesel chemistry dominates. Both the first-stage and the total ignition delay times increase with rising NH3energy fraction, but decrease with the increase of equivalence ratio. Then, an updated NH3/diesel kinetic mechanism was proposed by adding new cross reactions between diesel and NH3. Results show that the current mechanism exhibits an obvious improvement for ignition delay time prediction compared to the original mechanism, though it still fails to reproduce the ignition delay times of NTC range for the mixture containing 20% NH3. Further sensitivity analysis and the OH radical rate of production analysis indicate that the overestimation of the reactivity for the NH3/diesel fuel blends at NTC range is closely related to reaction NO+HO2double bondNO2+OH. The promoting effect of NO species on the conversion of inactive HO2radical into active OH radical at low temperature greatly accelerates the autoignition. In addition, the current mechanism does not include the cross reaction between the large NTC-related species (QOOH, OOQOOH, OQOOH, ROO) and the N-containing species (NO, NO2, NH2), especially for the NO related reactions, which may have a great impact on the IDT simulation of the NH3/diesel mixtures. Consequently, this work presents new ignition delay time measurements and mechanism optimization for NH3/diesel mixtures. Continuous works should be emphasized on these unclear reactions to further understand the combustion behavior of NH3/diesel fuel blends.