Abstract Di-n-butyl ether (DNBE) and n-octanol have very low sooting tendencies in diesel-like combustion, as demonstrated in previous engine studies. This finding is not fully understood for pure DNBE, because it has a very high cetane rating (∼100). In order to investigate the underlying mechanisms, the structure of diesel-type jets is analyzed by a number of optical diagnostics, such as spontaneous Raman scattering (SRS), laser-induced fluorescence (LIF), OH* luminescence imaging, Mie scattering, and shadowgraphy. Pure DNBE and a tailor-made blend of 50% DNBE and 50% n-octanol as well as neat n-heptane are used as the fuel in separate experiments. The jets are probed in a simulated engine-like environment in a high-pressure combustion vessel. In particular, the inner flame structure is analyzed by SRS and LIF. This yields information on the local temperature and the concentrations of O2, CO, and polycyclic aromatic hydrocarbons (PAH). For the first time, O2 is quantitatively detected in the core of a diesel-like flame by resonance-enhanced SRS. Thereby, air entrainment into the inner flame core is assessed. Results show that air entrainment is particularly strong for pure DNBE, explaining its high soot oxidation rate and overall low sooting tendency. High entrainment is primarily attributed to the low heat-release rate of DNBE, which is likely an effect of its high ignitability. Thus, it can be concluded that the high cetane rating of pure DNBE does not only lead to relatively poor pre-combustion mixture preparation and consequently considerable soot formation but seemingly also to particularly strong soot oxidation. Moreover, the jet structure turns out to be very similar for the DNBE/n-octanol blend and neat n-heptane, indicating that the net effect of volatility and fuel oxygenation is weak.

中文翻译：

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以 C8 氧化物为燃料的类柴油射流结构的激光光谱研究

摘要 二正丁基醚 (DNBE) 和正辛醇在类似柴油的燃烧中具有非常低的烟灰倾向，如先前的发动机研究所示。对于纯 DNBE，这一发现尚不完全清楚，因为它具有非常高的十六烷值（~100）。为了研究潜在的机制，柴油型射流的结构通过许多光学诊断进行分析，例如自发拉曼散射 (SRS)、激光诱导荧光 (LIF)、OH* 发光成像、米氏散射和影印术。纯 DNBE 和 50% DNBE 和 50% 正辛醇以及纯正庚烷的定制混合物在单独的实验中用作燃料。在高压燃烧容器中模拟类似发动机的环境中探测射流。特别是内部火焰结构通过 SRS 和 LIF 进行分析。这会产生有关当地温度和 O2、CO 和多环芳烃 (PAH) 浓度的信息。共振增强型 SRS 首次在类柴油火焰的核心中定量检测到 O2。因此，评估了进入内火焰核心的空气夹带。结果表明，纯 DNBE 的空气夹带特别强，这解释了其高烟灰氧化率和总体低烟灰倾向。高夹带主要归因于 DNBE 的低热释放率，这可能是其高可燃性的影响。因此，可以得出结论，纯 DNBE 的高十六烷值不仅会导致燃烧前混合物制备相对较差，从而导致大量烟灰形成，而且似乎还会导致特别强烈的烟灰氧化。而且，