CO₂ emission limits get constantly stricter over the years. One approach is the intensified usage of biofuels to reduce the overall CO₂ emissions. For this purpose, biofuels such as ethanol and butanol are increasingly blended with conventional gasoline fuel. Yet, under certain circumstances, ethanol- and butanol-blended gasoline can also lead to higher soot formation rates.^1,2 Ethanol blending may lead to a decrease in the evaporation rate due to its large evaporation enthalpy, which could also affect the soot formation and emission. For example, Trost et al.³ measured a higher evaporative cooling for ethanol compared to the gasoline surrogate fuel iso-octane. Chen and Stone⁴ found a continuous increase of particle mass and number with increasing ethanol percentage which also was ascribed to the high evaporation enthalpy. Storch et al.⁵ studied ethanol fuel blends in a direct-injection spark-ignition (DISI) spray at simplified cold start conditions (corresponding to late injection timing) within a constant volume chamber. Especially, E20 (single and multicomponent fuels containing 20 vol% of ethanol) showed larger soot volume fractions compared to the pure base fuel (which was observed for iso-octane and a multicomponent gasoline fuel) because of the changed spray processes. In these studies, the soot formation was mainly caused by droplet combustion originating from droplet clouds mostly located at the spray front.⁵ It was assumed that mainly large droplets exist in the spray front, which hardly evaporates because of the ethanol content.

中文翻译：

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使用两相结构化激光照明平面成像液滴尺寸分析乙醇和丁醇直喷火花点火喷雾

多年来，CO ₂排放限值不断严格。一种方法是加强使用生物燃料以减少总的CO ₂排放量。为此，生物燃料例如乙醇和丁醇越来越多地与常规汽油燃料混合。但是，在某些情况下，掺有乙醇和丁醇的汽油也会导致更高的烟尘形成率。^1,2乙醇共混物可能会由于蒸发焓高而导致蒸发速率降低，这也可能影响烟灰的形成和排放。例如，Trost等。与汽油替代燃料异辛烷相比，图³测得的乙醇蒸发冷却更高。陈和石⁴结果发现，随着乙醇百分比的增加，颗粒质量和数量不断增加，这也归因于高蒸发焓。Storch等。⁵研究了在恒定容积室内在简化的冷启动条件（对应于较晚的喷射正时）下以直接喷射式火花点火（DISI）喷雾器对乙醇燃料混合物进行的研究。特别是，E20（含有20％（体积）乙醇的单和多组分燃料）与纯基础燃料（异辛烷和多组分汽油燃料所观察到的）相比，显示出更大的烟so体积分数，这是因为改变了喷雾工艺。在这些研究中，烟灰的形成主要是由液滴燃烧引起的，该液滴燃烧源自主要位于喷雾前沿的液滴云。⁵ 假定主要是在喷雾前端存在大的液滴，由于乙醇含量的缘故，该液滴几乎不会蒸发。