# Effects of Ethanol-Diesel on the Combustion and Emissions from a Diesel Engine at a Low Idle Speed
## 3 Results and Discussion
### Combustion Characteristics
#### 3.1.2 Combustion Phase  
The combustion phase is known to directly affect the thermal efficiency of internal combustion engines. The mass fraction burned (MFB) provides a convenient way to analyze the phase of the combustion in the cylinder by the duration of the crank angle. The MFB is calculated by dividing the amount of accumulated heat during the combustion period by the total heat released [12,33]. From the start of fuel injection, the crank position where the MFB is 10% is noted as CA10, and the point where the MFB is 90% is noted as CA90. The difference between the fuel injection start point and CA10 is called the ignition delay, or the flame-development angle, and the difference between CA10 and CA90  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Test** & **Max Combustion** & **Location of** & **Max Heat Release** & **Location of** & **Ekhaust Gas** & **BSFC** & **BTE** \\
**Fuel** & **Pressure (P\({}_{max}\))** & **P\({}_{max}\)** & **Rate (HIRan)** & **HRRans** & **Temperature** & **(g/kWh)** & **(\%)** \\
**(Da)** & **(Ca)** & **(C\({}^{\prime}\)CA)** & **(\({}^{\prime}\)CA)** & **(\({}^{\prime}\)CA)** & **(K)** & **(g/kWh)** & **(\%)** \\ \hline DE\_0 & 58.3 & ATDC 11 & 28.64 & ATDC 7 & 501 & 336.9 & 24.3 \\ DE\_3 & 60.7 & ATDC 11 & 31.30 & ATDC 7 & 498 & 348.3 & 23.8 \\ DE\_5 & 60.1 & ATDC 11 & 31.86 & ATDC 8 & 495 & 350.3 & 23.8 \\ DE\_10 & 60.0 & ATDC 11 & 32.53 & ATDC 8 & 494 & 356.7 & 23.8 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Combustion characteristics under test conditions.  
Figure 4: (a) The BSFC and BTE, and (b) exhaust gas temperature with changing ethanol concentrations.  
is called the combustion duration, or the rapid-burning angle [33; 34; 35]. CA50 denotes where the MFB is 50%, which means that 50% of the injected fuel is converted to energy [36].  
Figure 5 shows the MFB for each fuel condition. Figure 5a is the initial area of combustion, which shows the CA10 location of each fuel condition, and (b) is the end of the MFB, which shows CA90. With an increasing ethanol blend ratio, CA10 is retarded from BTDC 8.0 \({}^{\circ}\)CA at DE_0 to BTDC 6.3 \({}^{\circ}\)CA at DE_10. With increasing ethanol, CA90 was retarded from ATDC 13.5 \({}^{\circ}\)CA, at DE_0, to ATDC 14.5 \({}^{\circ}\)CA, at DE_10. Figure 6 presents the ignition delay and combustion duration. As the ethanol in the blend is increased, the ignition delay is increased from 12.0 \({}^{\circ}\)CA to 13.7 \({}^{\circ}\)CA, and the combination duration decreased from 21.5 \({}^{\circ}\)CA to 20.8 \({}^{\circ}\)CA. This means that the combustion of the pilot injection becomes slower with an increased ethanol blend ratio, but the diffusion combustion after the main injection becomes faster. When ethanol is blended, the ignition delay increases due to the high evaporation latent heat and low cetane number of ethanol. As the diffusion combustion of the main injection is initiated, rapid combustion occurs due to the effect of oxygen added from the blended ethanol. Studies by [PERSON] et al. [18], [PERSON] [21] and [PERSON] et al. [22] also reported that blending ethanol or alcohol fuels increases the ignition delay due to the low cetane number and the cooling effect caused by the high latent heat of evaporation, and decreases the combination duration. CA50 is the point where the maximum heat release rate occurs at the center of the MFB profile, and is used to set the maximum brake torque of the engine. CA50 is retarded from ATDC 6.8 \({}^{\circ}\)CA to ATDC 7.6 \({}^{\circ}\)CA as the ethanol blend ratio increases. It is noted that these points are similar to the locations of HRRmax.