## 2 Materials and Methods
### Experimental Settings and Engine Test Rig  
A single-cylinder compression ignition (CI) naturally aspirated engine (Figure 1, Table 3) was used to carry out the tests. A diaphragm pump mounted in the crankcase was used to deliver high-pressure fuel to the injector, which was located at the center of the hemispherical bowl-in-piston combustion chamber. The mass flowrate of air draw during the intake process was measured via a differential pressure transducer mounted at the entrance of a plenum cylinder used to attenuate the pulsation of the intake process. The fuel mass flow rate was measured using a burette mounted in the pipe connecting the fuel tank to the fuel pump. The engine was loaded by a dynamometer--a car alternator modified for the purpose--with the load governed by a bridge rectification circuit that managed the external excitation and dissipated generated heat using an air-cooled resistive load bank. The rotational speed of the engine was sensed using a proximity switch, and an exhaust gas analyzer (EMS 5003) (Table 4) was used to measure the engine tailpipe emissions of CO2, CO, NOx, and HC.  
The emission trends were investigated under different engine loads (50, 75, and 100%) and for a range of engine speeds (1600-3600 rpm in steps of 200 rpm) to obtain a broad understanding of emission behaviors and a wide scale for comparison. The differences between the emission levels of the benchmark diesel (grade 2D) fuel and those of the biodiesel fuels were normalized with respect to the benchmark as \(M=(M_{b}-M_{d}/M_{d})\times 100\%\), where \(M\) is the normalized value, \(M_{b}\) is the biodiesel measurement, and \(M_{d}\) is the benchmark diesel measurement. Then, the normalized values were represented in a series of charts showing the percentage fractions of the variations as contour figures adjacent to their respective trends.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Property** & **DSO Biodiesel** & **Jatropha** & **ASTM D6751** & **ASTM D975** \\  & **Biodiesel** & **Biodiesel** & **Diesel** \\ \hline Flash point (\({}^{\circ}\)C) & 164 & 182.5 & \(>\)130 & 1D: 38 \\ Cloud point (\({}^{\circ}\)C) & +9.4 & 3 & Report & 2D: 52 \\ Cetane number (-) & 62 & 51 & 47 min. & 40 min. \\ Acid number (mg KOH:g\({}^{-1}\)) & 0.29 & 0.05 & 0.5 max. & - \\ Viscosity @ 40 \({}^{\circ}\)C (mm\({}^{2}\):s\({}^{-1}\)) & 4.38 & 4.38 & 1.9–6.0 & 1D: 1.3–2.4 \\ Heating value (MJ/kg) & 39.8 & 40.5 & - & 44.6 \\ Calcium \& Magnesium & 3.27 & - & 5 max. & - \\ combined (mg:kg\({}^{-1}\)) & & & 15 ppm for S15 & 1D and 2D \\ Sulfur (ppm) & 0.93 & 4.59 & grade; 500 ppm for & 15 ppm for S15 \\  & & & S500 grade & grade; 500 ppm for \\  & & & & S500 grade \\ Water \& sediment (vol.\%) & 0.019 & - & 0.05 max. & 0.05\% max. \\ Sulphated ash (wt.\%) & \(<\)0.02 & - & 0.020 max. & - \\ Carbon residue (wt.\%) & 0.023 & - & 0.050 max. & 1D: 0.15 max. \\ Phosphorous content (wt.\%) & 0.0002 & - & 0.050 max. & 2D: 0.35 max. \\ Distillation 90\% (\({}^{\circ}\)C) & 352.4 & - & 0.001 max. & - \\ Sodium \& potassium (ppm) & 3.2 & - & 360 max. & 1D: 288 max. \\ Oxidation stability (h @ 110 \({}^{\circ}\)C) & 7.4 b & 3 c & 6 min. & 110 \\ \hline \hline \end{tabular}  
* Data obtained from [13]; b considering EN 15751; \({}^{\circ}\) considering EN ISO 14112.  
\end{table}
Table 2: DSO biodiesel specifications compared with Jatropha biodiesel.