## 3 Results and Discussion
### Effects of EGR on FSR in the DF Mode  
This section analyzed the EGR influence on FSR and the combustion process in the DF mode. The evaluation was performed imposing typical Euro 6 engine-out NOx limit of 0.6 and 0.9 g/kWh for \(1500\times 5\) and \(2000\times 8\), respectively. The goal was to reach the same FSR values obtained by the multi-injection strategy.  
Figure 11 compares the FSR trends with and without EGR in \(1500\times 5\) test point varying combustion phasing in the range 4-12 deg. For a more advanced CA50 (4 deg), the FSR value achieved was very low (0.2) due to the high thermal inertia of ethanol/diesel mixture using a high rate of EGR. Ethanol fraction was reduced to sustain the combustion. Retarding the combustion phasing FSR increased and its trend was closer to the reference point in the range 10-12 deg CA50.  
The combined effects of the use of EGR and the high heat of vaporization of ethanol allow a reduction of in-cylinder temperature and pressure [21] delaying the start of combustion. The dilution effect, when EGR was used, means a decreased oxygen concentration in the intake charge and less favorable thermodynamic conditions to initiate combustion. As a consequence, the combustion process was more premixed, producing a higher rate of heat release, and the trend became more obvious with increasing ethanol fraction [11]. The higher premixed combustion phase enhanced the in-cylinder mean temperature and accelerated the post-combustion of premixed diesel and alcohol fuel, and thus shortened the combustion duration [38].  
Figure 11: Effect of EGR on the FSR function of CA50 in \(1500\times 5\) test point.  
Finally, it can be stated that, at the same engine speed-load, the combustion process, in terms of the HRR pattern, as shown in Figure 11, was similar within the CA50 range considered.  
With an imposed limit of 0.9 g/kWh, in 2000 \(\times\) 8 test point, over the CA50 range 6-12 deg, the fraction of ethanol injected was always lower than the reference one, as reported in Figure 12. As previously stated, delayed combustion was observed with a prominent premixed combustion phase, which affected noise, in an average of 1 dBA, in the whole CA50 range considered.  
Figure 13 shows the influence of EGR on combustion efficiency, and PM indicated specific emissions for both test points.  
For both test points, a general improvement of the combustion efficiency was observed within the CA50 range considered. It was reasonably due to a richer combustion process as lower air index (\(\lambda\)) values shown in Figure 14.  
Figure 12: Effect of EGR on the FSR function of CA50 in 2000 \(\times\) 8 test point.  
Figure 13: Influence of EGR on combustion efficiency and PM specific emissions.  
The ethanol addition could improve the PM reduction due to lower oxygen availability in the presence of EGR. As can be seen, the PM emission trend adopting EGR, at \(1500\times 5\), was lower than the reference one except for an abrupt variation at 4 deg of CA50 due to the greater amount of diesel injected. For higher load, at 6 deg of CA50, the lower fraction of ethanol injected led to a PM penalty. Nevertheless, retarding combustion phasing the trend decreased due to the further FSR increment.