Biodiesel is a good alternative to Petroleum Diesel (PD). The storage of fuel is unavoidable for its future use. The objective of the study was to investigate ultrasonic parameters: viscosity, relaxation time, ultrasonic absorption and Gibb’s free energy for 2-year long-term stored biodiesels and blends with PD. The two biodiesels were Cotton Seed Oil Methyl Esters (CSOME) and Palm Stearin Methyl Esters (PSME). Five biodiesel blends with PD in 10, 20, 30, 40 and 50 volume per cent were studied at the room temperature of 301 K. The fatty-acid profiles were also investigated using GC–MS chromatographic analytical tool and the viscosity was determined using an Ostwald viscometer. Ultrasonic velocity was measured with an ultrasonic interferometer of fixed frequency 2 MHz. The results show that CSOME biodiesel contains 13.47 and 86.53 weight per cent of low molecular weight nonpolar and high molecular weight polar compounds, respectively, and PSME biodiesel with 38.66% and 61.33%, respectively. The measured parameters increased for both the biodiesel blends due to storage. The increase in CSOME blends is more than that in PSME blends. For CSOME blends, highest and lowest changes are 64.28% and 4.48% for 10% volume blend of viscosity and pure CSOME biodiesel of Gibb’s free energy, respectively. In PSME blends, they are 31.25% for 10% volume blend of viscosity and zero for 50% volume blend of Gibb’s free energy. The highest difference occurred for 50% volume blends between old CSOME and PSME blends. From the overall results, it is concluded that variations of the measured parameters strongly depend on the fatty-acid profile of biodiesels due to storage.

生物柴油是石油柴油（PD）的良好替代品。燃料的储存在将来的使用中是不可避免的。该研究的目的是研究超声参数：粘度，弛豫时间，超声吸收和吉布的2年长期储存生物柴油及其与PD混合物的自由能。两种生物柴油是棉籽油甲基酯（CSOME）和棕榈硬脂甲基酯（PSME）。在301 K的室温下研究了5种生物柴油的10％，20％，30％，40％和50％的PD掺混物。还使用GC-MS色谱分析工具研究了脂肪酸分布，并使用奥斯特瓦尔德粘度计。用固定频率为2MHz的超声波干涉仪测量超声波速度。结果显示CSOME生物柴油包含13.47和86。低分子量非极性化合物和高分子量极性化合物分别占53％（重量）和PSME生物柴油，分别占38.66％和61.33％。由于储存，两种生物柴油混合物的测量参数均增加。CSOME共混物的增加量大于PSME共混物的增加量。对于CSOME共混物，对于吉布自由能的10％体积粘度和纯CSOME生物柴油，最高和最低变化分别为64.28％和4.48％。在PSME混合物中，吉布的自由能的10％体积比为31.25％，50％体积比为零。最大的差异发生在旧CSOME和PSME混合物之间的50％体积混合物中。从总体结果可以得出结论，由于储存，测量参数的变化很大程度上取决于生物柴油的脂肪酸谱。