Composition and Fuel Properties
The fatty acid concentration profiles and fuel properties of CaME, PME and SME are summarized in Tables S1 and S2 in the supporting information. These results were discussed in full in an earlier study (Dunn, 2020) and a summary of those findings are presented herein.
Analysis of the FAME concentration profiles (Table S1 ) showed that the SME had a higher total PUFAME concentration (62.09 mass%) and a lower total MUFAME concentration (21.67 %) than either CaME (26.8 and 65.74 %) or PME (9.7 and 40.49 %). CaME had the lowest total SFAME concentration (7.40 %) followed by SME (16.21 %) and PME (49.82 %). SME had the highest calculated iodine value (IV) = 132.76 g I2100−1g−1, followed by CaME (109.6) and PME (51.8).
Selected fuel properties of the three biodiesel fuels were summarized inTable S2 . In descending order, IPR at 110 °C was 9.34 h, 7.71 h and 2.745 h for CaME, PME and SME. The low value for SME was expected given its high total PUFAME content and comparable with data reported in other studies (Moser, 2008a, 2014, 2016; Yang et al., 2013). The experimental IPR value for CaME was also comparable with data reported in the literature (Joshi et al., 2009; Moser, 2008b; Yang et al., 2013). However, the IPR of PME was lower than that of CaME, despite PME having a lower total PUFAME concentration. Generally higher IPR values (9.2-15.2 h) were reported for PME in the literature (Moser, 2008b, 2016; Sarin et al., 2010; Shahabuddin et al., 2012). In the earlier study (Dunn, 2020), it was postulated that PME had undergone partial degradation before its use in the study. PME had AV = 0.72 mg KOH g−1(Table S2 ), a value that exceeded the maximum limit (0.50 mg KOH g−1) in the ASTM biodiesel fuel standard specification D6751 (ASTM, 2021). This higher value may have indicated that PME had undergone hydrolytic degradation. PME also exhibited a PV = 11.3 meq kg−1 (Table S2 ), a value that was nearly twice the PV measured for CaME. Trace concentrations of hydroperoxides are known to act as autoxidation initiators (Frankel, 2005a; Kamal-Eldin and Yanishlieva, 2005). The effects of high AV and PV suggested that PME may have experienced autoxidation before being used in the study.
The pure MeC18:1 and MeC18:2 samples were also analyzed for IPR. At 110 °C, IPR = 2.12 ± 0.05 h for MeC18:1, a value that was comparable with data reported in other studies (Knothe, 2008; Moser, 2009). Those studies also reported IPR = 0.94 h and 1.0 h for MeC18:2. Nevertheless, no reliable IPR data were obtained for MeC18:2 at 110°C in the present study.