# Heat Release Rates of Straight Soybean and Diesel Oil Blends in a Compression Ignition Engine
## 3 Results and Discussion
### Heat Release Rate  
The heat release rate and the corresponding cumulative energy release obtained for the fuels at 1800 and 2100 are presented in Figures 3 and 4, respectively. The heat release rate curves evidence the premixed and nonpremixed (diffusive) combustion phases. Additionally, a significant residual combustion phase is also observed. The heat release rate increases with the load, i.e., with the speed reduction, where the mass fuel injected per cycle increases. Observing the curves of cumulative energy release, the combustion performance presented a similar behavior in the premixed combustion phase for all fuels tested, changing in the nonpremixed combustion phase, where we observed a significant difference among the fuels. The heat release rate in the premixed combustion phase is influenced by the ignition delay. Consequently, for both engine speeds, one observes that all fuels present a similar premixed combustion phase, corresponding to a similar ignition delay, as shown in Table 6. In the case of the blend 80S/20D(85), the heat release curve begins slightly delayed as a \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Engine Speed (rpm)**} & \multirow{2}{*}{**Fuel**} & **Start of** & **Ignition** & **Ignition** \\  & & **(\({}^{\circ}\) CA)** & **(\({}^{\circ}\) CA)** & **(\({}^{\circ}\) CA)** & **(\({}^{\circ}\) CA)** \\ \hline
1800 & 100D(25) & 345.0 & 352.5 & 7.5 & 0.694 \\  & 50S/50D(25) & 345.0 & 352.5 & 7.5 & 0.694 \\  & 50S/50D(85) & 345.5 & 353.0 & 7.5 & 0.694 \\  & 80S/20D(85) & 345.5 & 354.0 & 8.5 & 0.787 \\ \hline
2100 & 100D(25) & 345.0 & 353.5 & 8.5 & 0.675 \\  & 50S/50D(25) & 344.5 & 353.0 & 8.5 & 0.675 \\  & 50S/50D(85) & 345.0 & 353.5 & 8.5 & 0.675 \\  & 80S/20D(85) & 345.0 & 354.5 & 9.5 & 0.754 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Ignition delay of the fuel tested at 1800 rpm. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Engine Speed (rpm)**} & \multirow{2}{*}{**Fuel**} & **Maximum** & **Difference** & **Angle at Maximum** \\  & & **Pressure (kPa)** & **(\%)** & **Pressure (\({}^{\circ}\) CA)** \\ \hline
1800 & 100D(25) & 6584.7 \(\pm\) 22.4 & & 366.5 \\  & 50S/50D(25) & 6557.7 \(\pm\) 19.3 & \(-\)0.41 & 366.5 \\  & 50S/50D(85) & 6484.8 \(\pm\) 23.1 & \(-\)1.52 & 366.5 \\  & 80S/20D(85) & 6204.8 \(\pm\) 36.0 & \(-\)5.77 & 365.0 \\ \hline
2100 & 100D(25) & 6395.1 \(\pm\) 25.6 & & 365.5 \\  & 50S/50D(25) & 6413.3 \(\pm\) 19.1 & 0.28 & 365.5 \\  & 50S/50D(85) & 6234.6 \(\pm\) 26.1 & \(-\)2.51 & 365.5 \\  & 80S/20D(85) & 6152.3 \(\pm\) 16.2 & \(-\)3.80 & 364.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Maximum pressure and percentage difference relative to diesel oil at 1800 and 2100 rpm. result of its ignition delay that is slightly higher with respect to the other fuels. At 1800 rpm, the higher premixed combustion rate is related to the load increase and the time increase per each crank angle degree corresponding to the speed reduction, which favors the air-fuel mixing and the burning. At 1800 rpm, the diesel oil 100D(25) and the blends 50S/50D(25) and 50S/50D(85) presented the highest peak of the heat release rate in the diffusive phase. From 380\({}^{\circ}\) CA, approximately, the heat release rate increased for the blend 80S/20D(85) in comparison with the other fuels (residual combustion phase), which shows the combustion delay of this blend and the effect of the highest oxygen content in the fuel that favors the burning, such that the cumulative energy release is high for the blends 80S/20D(85) and 50S/50D(85). The 100D(25) oil presented the lowest cumulative energy release. Similar results were reported by [PERSON] et al. [45] in their work with oxygenated fuels. At 2100 rpm, the diesel oil 100D(25) and the blend 80S/20D(85) presented the highest peak of the heat release rate in the diffusive phase. In the residual combustion phase, the blend 80S/20D(85) presented the highest heat release rate.