## 3 Results and Discussion
### C. tinctoria Biodiesel Properties  
After purification of the _C. tinctoria_ biodiesel, the biodiesel yield was calculated by Equation (1). The results show that the biodiesel yield from the oil is 84%. In order to investigate the properties of _C. tinctoria_ biodiesel as a new resource, the physicochemical characteristics of the produced biodiesel was measured. In Table 3, the physicochemical characteristics of the _C. tinctoria_ biodiesel is presented. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Physico-Chemical Parameters** & **Unit** & **Content** \\ \hline Oil content & \% & 26 \\ Weight of 1000 seeds & g & 15 \\ Density & g/cm\({}^{3}\) & 0.872 \\ Kinematic viscosity & mPa s & 4.32 \\ Acid value & Mg KOH/g oil & 2.5 \\ Iodine value & g l2/100 g oil & 170 \\ Water content & mg/g & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physico-chemical properties of the _C. tinctoria_ seed oil. Figure 3: _C. tinctoria_ biodiesel production process. According to the results, it is obvious that all the physicochemical characteristics of the produced biodiesel are in agreement with the ASTM standards. Viscosity is one of the important properties of biodiesel. By considering the biodiesel standard (ASTM), the viscosity of a biodiesel should be in the range of 1.9-6.0 mm\({}^{2}\)/s. The results show that the viscosity of _C.__tinctoria_ biodiesel is 3.74 mm\({}^{2}\)/s, which is lower than different biodiesel resources; for example, moringa (5 mm\({}^{2}\)/s) [47], karanja (6.13 mm\({}^{2}\)/s) [48], and neon (5.21 mm\({}^{2}\)/s) [47]. Another important characteristic of a biodiesel resource is its density. Density plays an important role in the fuel atomization in the combustion process of a diesel engine [49]. Based on the biodiesel standards (ASTM and EN), the range of a new biodiesel resource should be 0.86-0.9 (g/cm\({}^{3}\)). The result of the present study shows that the density of _C.__tinctoria_ biodiesel is 0.862 (g/cm\({}^{3}\)). By reviewing the recent studies, it is clear that the density of the _C.__tinctoria_ biodiesel is lower than many of the other resources, such as karanja (0.931 g/cm\({}^{3}\)) [48], moringa (0.883 g/cm\({}^{3}\)) [47], rapeseed (0.882 g/cm\({}^{3}\)) [47], and tobacco (0.888 g/cm\({}^{3}\)) [48]. Another biodiesel property that plays an important role in the corrosion of the internal parts of diesel engines, is the acid number. The ASTM standard consider a strict law for acid number. Based on the ASTM standard, the acid number of a new biodiesel should not exceed 0.5 mg KOH/g. According to the result of the present study, the acid number value of the _C.__tinctoria_ biodiesel is 0.41 mg KOH/g. So, this acid number is suitable for a new biodiesel resource. In this present study, other properties of the _C.__tinctoria_ biodiesel have been measured, including the cloud point, pour point, and flash point. The results show these properties of the _C.__tinctoria_ biodiesel pass the ASTM standard. It is noteworthy that the specification properties of the _C.__tinctoria_ biodiesel are within the ASTM standard range and that the biodiesel produced from _C.__tinctoria_ seed oil can be used as a suitable fuel source instead of petroleum-derived fuels. \begin{table}
\begin{tabular}{c c} \hline \hline
**Fatty Acid** & **Content (\%)** \\ \hline Palmitic acid (C16:0) & 5.32 \(\pm\) 0.047 \\ Palmitoleic acid (C16:1) & 0.11 \(\pm\) 0.50 \\ Stearic acid (C18:0) & 3.15 \(\pm\) 0.19 \\ Oleic acid (C18:1) & 13.99 \(\pm\) 029 \\ Linoleic acid (C18:2) & 76.68 \(\pm\) 0.16 \\ Linoleic acid (C18:3) & 0.67 \(\pm\) 0.13 \\ \(\sum\) UFA & 91.45 \\ \(\sum\) SFA & 8.43 \\ \(\sum\) MUFA & 14.10 \\ \(\sum\) PUFA & 77.35 \\ \(\sum\) UFA: \(\sum\) SFA & 10.85 \\ \(\sum\) MUFA: \(\sum\) PUFA & 0.18 \\ \hline \hline \end{tabular} Note: UFA, unsaturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; SFA, saturated fatty acids.  
\end{table} 
Table 2: Fatty acid composition of oil extracted from _C.__tinctoria_ seeds.