Abstract The flammability limit is a hurdle to realizing ultra-lean combustion and achieving high thermal efficiency in spark ignition engines. Hydrogen, known for its wide explosion limits, has been utilized in gasoline to improve the lean limit. The influence of hydrogen on lean flammability limits of isooctane was studied at initial temperatures of 393–513 K and an ignition energy (IE) of 3000 mJ, while the burning characteristics were studied at an initial temperature of 393 K and IE = 37 mJ. It is found that a spherical flame appeared when the isooctane–air–H2 mixture was ignited from λ = 0.8 to λ = 1.2 at IE = 37 mJ, whereas a leaner mixture was burnt at IE = 3000 mJ with unstable flame growth during the early stage. Flame instability eventually evanesced and buoyancy was observed near the lean limits. The lean limits of isooctane–air increased to 2.1λ with 0–90% hydrogen. Raising the initial temperature from 393 to 513 K increased the lean limits of isooctane–air–H2 to 0.2λ. Hydrogen obtained from CH2O (C, H, and O species) makes a considerable contribution to improving the burning near the lean limits. The mole fraction of the short-lived radicals H, OH, and O decreased when the excess air coefficient moved toward the lean limits and increased by introducing hydrogen, which improved the lean flammability limits and burning velocity.

中文翻译：

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氢对异辛烷-空气混合物的贫燃极限和燃烧特性的影响

摘要 可燃极限是火花点火发动机实现超稀薄燃烧和实现高热效率的障碍。氢气以其广泛的爆炸极限而闻名，已被用于汽油中以改善贫油极限。在 393-513 K 的初始温度和 3000 mJ 的点火能量 (IE) 下研究了氢气对异辛烷贫燃极限的影响，而在 393 K 和 IE = 37 mJ 的初始温度下研究了燃烧特性。发现当异辛烷-空气-H2 混合物在 IE = 37 mJ 下从 λ = 0.8 点燃到 λ = 1.2 时出现球形火焰，而较贫的混合物在 IE = 3000 mJ 下燃烧，早期火焰增长不稳定阶段。火焰的不稳定性最终消失了，并且在贫油极限附近观察到了浮力。异辛烷-空气的贫油极限增加到 2.1λ，含 0-90% 的氢气。将初始温度从 393 K 提高到 513 K 将异辛烷-空气-H2 的贫油极限增加到 0.2λ。从 CH2O（C、H 和 O 物种）获得的氢气对改善贫燃极限附近的燃烧做出了相当大的贡献。当过量空气系数向贫燃极限移动时，短寿命自由基 H、OH 和 O 的摩尔分数降低，并通过引入氢气增加，从而提高了贫燃极限和燃烧速度。