# Heat Release Rates of Straight Soybean and Diesel Oil Blends in a Compression Ignition Engine
## 2 Experimental Procedure  
### Fuels  
The fuels tested were diesel oil and two blends of soybean and diesel oil. The blends tested were 50/50% \(v/v\) soybean and diesel oils and 80/20% \(v/v\) soybean and diesel oils. Table 1 shows the fuels tested with their respective label and temperature for testing. The blend of 50/50% \(v/v\) was tested at two temperature levels. The high level (85 \({}^{\circ}\)C) was determined in order to obtain a similar break-up regime to diesel oil at 25 \({}^{\circ}\)C. This condition was evaluated following the criterion for the onset of jet atomization reported by [PERSON] and [PERSON] [36]. Density, dynamic viscosity, and surface tension are significant physical properties in the atomization process. These properties were tested for diesel and soybean oils and their blends at different temperatures ranging from 25 \({}^{\circ}\)C to 85 \({}^{\circ}\)C. Subsequently, correlations were proposed as a function of the temperature and volume fraction of soybean oil, allowing the calculation of the fuel properties at different injection conditions. These correlations were previously reported by [PERSON] et al. [37], and some measurements of the physical properties tested are presented in Table 2, including the respective expanded uncertainties. One can observe the increase in the density, dynamic viscosity, and surface tension with an increase in the percentage of vegetable oil in the blend, as well as the effect of heating on the reduction in these properties.  
Soybean oil tested suffered no refining or transesterification, only filtering. Vegetable oils are composed of fatty acid triglycerides, which determine the different physical and chemical properties of each vegetable oil. The diesel oil tested was commercial Brazilian diesel oil (known as diesel S10). The commercial Brazilian diesel oil used had a volumetric addition of 8% of biodiesel in accordance with national regulations. Currently, the com  
\begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Fuel**} & **Injection** & **Label** \\  & **Temperature** (\({}^{\circ}\)**C**) & **100D(25)** \\ \hline \multirow{2}{*}{\(50/50\%\)\(v/v\) soybean/diesel} & 25 & 50S/50D(25) \\  & 85 & 50S/50D(85) \\  & 85 & 80S/20D(85) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Identification of the fuels tested and the respective injection temperatures.  
mercial Brazilian diesel oil carries 13% (vol.) of biodiesel in its formulation [3]. The higher heating value (\(HHV\)), lower heating value (\(LHV\)), and elemental chemical composition were measured for soybean and diesel oils, and the respective results are presented in Table 3. In relation to \(LHV\), the highest content of carbon and hydrogen in diesel oil influences its \(LHV\), which is about 13% higher than the \(LHV\) of soybean oil. An empirical formula of soybean oil was calculated from the content of carbon, hydrogen, and oxygen. The molecular formula of soybean oil was estimated from its empirical formula and the assumption of soybean oil as a triglyceride (a molecule with six atoms of oxygen). Diesel oil was modeled as dodecane.