Biodiesel is a promising alternative fuel for diesel engines, but its high viscosity and low volatility have limitations in decreasing emissions. As a renewable alternative fuel with a high oxygen content, ethanol blended with biodiesel can decrease kinematic viscosity and improve fuel evaporation. In this study, the effects of the ethanol addition ratio on the spray, combustion, and emission performances of a diesel engine fuelled with biodiesel were investigated. The spray characteristics were measured using a high-speed camera and Malvern laser analysis, whereas the combustion and emission performances were tested on a turbocharged common rail direct injection (CRDI) diesel engine. The results show that adding ethanol to biodiesel enlarges the spray cone angle (SCA) and shortens spray tip penetration (STP). In addition, the curves of the size–volume distribution (SVD) of the atomized fuel droplets move toward a smaller diameter, and the Sauter mean diameter (SMD) of the biodiesel–ethanol (BE) blends gradually decreases with increasing ethanol proportion. At low loads, the fuel injection strategy is multi-injection, and the peak cylinder pressures (PCPs) of BE blends are 0.77–1.96% higher than that of diesel at different ethanol blending ratios. However, the peak heat release rates (PHRRs) of BE blends are 9.3–11.5% higher than that of diesel owing to a faster combustion rate, longer main-injection duration, and more hydroxyl radicals generated in the pilot-injection stage. At medium–high loads, the injection strategy changes to single injection, the PCPs of BE blends are roughly equivalent to that of diesel, and the PHRRs of BE blends for different ethanol blending ratios are 9.76–11.91% lower than that of diesel. This is because of the lower diffusion combustion ratio, lower heat value, and change of injection duration corresponding to the variation in fuel properties. In addition, the results of the peak pressure rise rate and the cyclic variation indicate that the higher ethanol addition ratio increases the combustion noise and decreases the combustion stability. In terms of exhaust emissions, compared with biodiesel, with increasing ethanol blending ratio, the soot emissions for different BE blends decrease by 11.28–47.23%, the NOx emissions increase by 2.68–7.04%, and the HC emissions increase by 9.99–21.47%. Considering the engine performance comprehensively, a 20% ethanol blending ratio in biodiesel is recommended.

中文翻译：

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使用生物柴油-乙醇混合物运行的 CRDI 柴油机喷雾特性、燃烧稳定性和排放性能的实验研究

生物柴油是一种很有前景的柴油发动机替代燃料，但其高粘度和低挥发性在减少排放方面受到限制。作为一种高氧含量的可再生替代燃料，乙醇与生物柴油混合可以降低运动粘度并改善燃料蒸发。在这项研究中，研究了乙醇添加比例对生物柴油柴油机喷雾、燃烧和排放性能的影响。使用高速摄像机和马尔文激光分析来测量喷雾特性，而燃烧和排放性能则在涡轮增压共轨直喷（CRDI）柴油发动机上进行测试。结果表明，在生物柴油中添加乙醇会增大喷雾锥角（SCA）并缩短喷雾尖端穿透力（STP）。此外，雾化燃料液滴的尺寸-体积分布（SVD）曲线向更小的直径移动，生物柴油-乙醇（BE）混合物的索特平均直径（SMD）随着乙醇比例的增加而逐渐减小。低负荷时，燃油喷射策略为多次喷射，不同乙醇混合比例下，BE混合物的气缸峰值压力（PCP）比柴油高0.77%~1.96%。然而，BE 混合物的峰值放热率 (PHRR) 比柴油高 9.3-11.5%，因为其燃烧速率更快，主喷射持续时间更长，并且在预喷射阶段产生更多的羟基自由基。中高负荷时，喷射策略改为单次喷射，BE混合物的PCP与柴油大致相当，不同乙醇混合比例的BE混合物的PHRR比柴油低9.76%~11.91%。这是因为较低的扩散燃烧比、较低的热值以及与燃料性质的变化相对应的喷射持续时间的变化。此外，峰值压力上升率和循环变化的结果表明，较高的乙醇添加比例会增加燃烧噪声并降低燃烧稳定性。在废气排放方面，与生物柴油相比，随着乙醇掺混比例的增加，不同BE掺混物的烟尘排放量下降了11.28%~47.23%，NOx排放量增加了2.68%~7.04%，HC排放量增加了9.99%~21.47%。 。综合考虑发动机性能，建议生物柴油中乙醇混合比例为20%。