Abstract Whilst fossil fuels have been an industrial driver for many decades, environmental concerns related to global warming have driven the development of alternative energy sources, such as the generation of biodiesel from vegetable oils. For a biodiesel to be commercialised, it must meets property and quality requirements from International Standards. Most of these checks must be performed off-line, with significant costs in terms of shutdown time and testing. On the other hand, ultrasound measurement can provide an in-line monitoring tool to assess the advance of transesterification. Although this was highlighted in previous works, hitherto this has not been the subject of a detailed metrological approach to define the uncertainty associated with ultrasound techniques applied to biodiesel and related liquids. This paper presents such research and addresses measurement of two ultrasound parameters, Speed of Sound (SoS) and attenuation coefficient (Att), and their capability of assessing macroscopic characteristics of the biodiesel. The liquids tested were pure edible oils (vegetable, corn, and sunflower), castor oil, pure biodiesel (B100), as well as blends of biodiesel with common contaminants or by-products related to biodiesel transesterification. Details of the biodiesel manufactured were varied, using different stirring speeds of rotation (200 rpm and 550 rpm), temperatures (40 °C and 50 °C), and KOH catalyst concentrations (0.2% and 1.5%). Contaminants added to pure biodiesel were methanol (0.10% and 0.20%), glycerol (0.10% and 0.15%) and triglyceride (2%). The acoustic characteristics of these liquids were determined relative to water using a broadband through-transmission substitution method covering the frequency range 1–20 MHz. Normalized error analysis has been applied to assess the equivalence of experimental results, as well as to discriminate the detection sensitivity of the technique. From the measurements, all edible oils showed equivalent experimental values for SoS and Att over the usable frequency band 2 MHz to 18 MHz. In contrast, biodiesel produced from sunflower and different reaction routes led to SoS and Att which were statistically different over the same frequency range, reflecting the ability of ultrasound to monitor low-level contamination of different blends. Finally, the paper concludes that ultrasound shows promise as a means of assessing biodiesel quality and purity with sensitivity sufficient to discern contaminants in a proportion as low as 0.1% in mass for Att measurements.

中文翻译：

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超声波参数测量作为评估生物柴油生产质量的一种手段

摘要 虽然化石燃料几十年来一直是工业驱动力，但与全球变暖相关的环境问题推动了替代能源的发展，例如从植物油中生产生物柴油。对于商业化的生物柴油，它必须符合国际标准的特性和质量要求。大多数这些检查必须离线执行，在停机时间和测试方面成本很高。另一方面，超声测量可以提供一种在线监测工具来评估酯交换的进展。尽管这在以前的工作中得到了强调，但迄今为止，这还不是定义与应用于生物柴油和相关液体的超声技术相关的不确定性的详细计量方法的主题。本文介绍了此类研究并解决了两个超声参数、声速 (SoS) 和衰减系数 (Att) 的测量，以及它们评估生物柴油宏观特性的能力。测试的液体是纯食用油（蔬菜、玉米和向日葵）、蓖麻油、纯生物柴油 (B100)，以及生物柴油与常见污染物或与生物柴油酯交换相关的副产品的混合物。生产的生物柴油的细节是多种多样的，使用不同的搅拌转速（200 rpm 和 550 rpm）、温度（40 °C 和 50 °C）和 KOH 催化剂浓度（0.2% 和 1.5%）。添加到纯生物柴油中的污染物是甲醇（0.10% 和 0.20%）、甘油（0.10% 和 0.15%）和甘油三酯（2%）。这些液体的声学特性是使用覆盖 1-20 MHz 频率范围的宽带传输替代方法确定的。归一化误差分析已被应用于评估实验结果的等效性，以及区分该技术的检测灵敏度。从测量结果来看，所有食用油在 2 MHz 到 18 MHz 的可用频段内都显示出等效的 SoS 和 Att 实验值。相比之下，由向日葵和不同反应途径生产的生物柴油导致 SoS 和 Att 在相同频率范围内具有统计学差异，反映了超声波监测不同混合物低水平污染的能力。最后，