# A Comprehensive Review of the Application Characteristics of Biodiesel Blends in Diesel Engines
## 3 Engine Performance  
### Brake Specific Fuel Consumption  
Brake specific fuel consumption (BSFC) represents the ratio of engine fuel consumption rate and brake power. BSFC is usually affected by some factors such as fuel calorific value, viscosity, density and volume fuel injection system [39]. BSFC is an important indicator to evaluate the fuel economy of the engine. Under the same operating conditions, a lower BSFC indicates better fuel economy. BSFC can be generally obtained by the formula [40]:  
\[\text{BSFC}=\frac{\dot{m_{f}}}{2\pi NT_{e}} \tag{1}\]  
Here, \(\dot{m_{f}}\) is the fuel consumption flow rate, \(N\) is the operating speed, and \(T_{e}\) is the brake torque.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Trenels Compared to Conventional Diesel**} \\ \cline{2-7}  
Most studies [4; 7; 8; 25; 26; 27] have found that biodiesel and its blends have a larger BSFC compared to conventional diesel. [PERSON] et al. found that Moringa oleifera biodiesel-diesel blends have lower BSFC values than diesel at all speeds [26]. [PERSON] et al. also obtained similar results [7]. They found that when the brake mean effective pressure (BMEP) is 0.34 MPa, the BSFC values of coconut biodiesel-diesel blends B10 (blends containing 10 vol% biodiesel), B20, B30, B50 are 0.8%, 2.1%, 3.5%, and 7% higher than diesel, respectively. The researchers also found that BSFC increases with the proportion of biodiesel in the fuel [7; 28; 32; 41]. Meanwhile, a few studies showed that biodiesel has less BSFC than diesel. [PERSON] et al. tested fuel blends containing different concentrations of palm, jatropha and calophyllum inophyllum biodiesel at different speed conditions. They found that the CIB10 (fuel blended with 10% calophyllum inophyllum biodiesel) consumes less fuel, as shown in Figure 1[29]. The higher BSFC of biodiesel is largely attributed to its lower calorific value, higher density and viscosity [7]. Due to the lower calorific value, more biodiesel is needed to compensate for the lower amount of heat released [4; 7]. The greater density allows more biodiesel to be used than conventional diesel when the same volume is injected, while the larger viscosity affects the volumetric fuel injection rate [29]. The combined effect of these factors leads to a lower BSFC of biodiesel. Different fuels tested on different engines with different test conditions have different BSFC. However, most of the research results indicated that BSFC increases with an increase in the percentage of biodiesel in the biodiesel-diesel blends when it is used as a fuel in conventional CI engines compared to diesel. The BSFC of several common biodiesel-diesel blends is listed in Table 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Engine** & **Test Condition** & **Test Fuels** & \begin{tabular}{c} **Blend** & \begin{tabular}{c} **Increase Rate** \\ **Ratio** \\ \end{tabular} & **Ref.** \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Single cylinder, direct \\ injection diesel engine, \\ 582 cc \\ \end{tabular} } & An average value for the & \multirow{4}{*}{
\begin{tabular}{c} Diesel blend with \\ (14; 16; 18), 2000 rpm \\ \end{tabular} } & B10 & 2.72 \\ \cline{3-4}  & & & B20 & 2.3 \\ \cline{3-4}  & & & B30 & 4.08 \\ \cline{3-4}  & & & B50 & 7.12 \\ \cline{3-4}  & & & B10 & 2.94 \\ \cline{3-4}  & & & B30 & 7.21 \\ \cline{3-4}  & & & B50 & 12.04 \\ \cline{3-4}  & & & B100 & 22.83 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Different brake specific fuel consumption results using biodiesel–diesel blends compared to diesel fuel in diesel engines.  
Figure 1: Brake specific fuel consumption of diesel and biodiesel blends at various engine speeds [29].