## 3 Results and Discussion
### Effects of the Nozzle Hole Numbers on FSR in the DF Mode  
This section aimed to cover the scientific gap in technical literature providing further information and discussion on the influence of the nozzle-hole number, 7 and 9, of the diesel injector on the maximum FSR reachable in the DF combustion mode and the GHG and PM emissions. All test conditions imposed in previous sections were kept constant to discriminate the nozzle effect. Relating to the 9 nozzle-hole cases, in \(1500\times 5\), the ethanol fraction increased retarding combustion phasing. On average, the FSR trend showed comparable values with the lower holes case in the range 6-10 deg of CA50, while at 4 and 12 deg higher values were reached as shown in Figure 15.  
The increasing of the nozzle holes diminished the reacting zone at a high temperature because of a more uniform distribution of the fuel and temperature, as confirmed in [PERSON] et al. [39]. Therefore, retarding combustion phasing a reduction of temperature on average was expected, as the HRR profiles of 9 holes case shown in Figure 15.  
For higher engine speed-load (\(2000\times 8\)), instead, the FSR values were not influenced by a different nozzle hole number, as shown in Figure 16. A slight difference could be observed for more retarded combustion phasing. For both nozzle cases, the FSR trend  
Figure 14: Air index with and without EGR: \(1500\times 5\) and \(2000\times 8\). Figure 15: FSR function of CA50 in \(1500\times 5\) test point, 9 holes vs. 7 holes. In terms of the combustion process, no relevant difference could be noticed in the HRR pattern. An exception was at 12 deg where the combustion occurred earlier with a lower temperature premixed phase as shown by the lower HRR peak. Furthermore, a prominent diffusive phase could be observed. The combustion characteristics related to different nozzle hole number are depicted in Figure 17. As can be seen, at lower load (5 bar BMEP) the 9 holes case showed the shortest combustion duration compared to the 7 holes case, with a maximum reduction of 5.5 deg at 4 deg aTDC and an average reduction of 2 deg retarding combustion phasing. In the DF combustion mode, when two fuels with different reactivity were involved in the combustion process, the combustion started in the high reactivity regions and gradually evolved towards low reactivity regions [40]. The increase in the nozzle hole number led to a reduction of the orifice diameter and, since it had the same hydraulic flow rate, an improvement of fuel atomization hence a better mixing of the charge. The formation of a higher reactivity zone in the combustion chamber and the more atomized fuel allowed shorter combustion duration. The charge cooling effect of the ethanol fraction combined with well mixed air-fuel led to an increase of ID. Shorter combustion duration was also observed for the higher load case. A discrepancy was found at 12 deg of CA50. In this case, due to lower mean temperature and a prolonged diffusive phase, as shown in Figure 16, increased combustion duration was observed. In the range 6-10 deg, the lower value of FSR shortened the ID. At a lower load, the 9-hole nozzle shows an improvement in the combustion noise compared to the 7-hole one with values aligned with the conventional diesel mode. In \(2000\times 8\), for both nozzles tested, the effect of ethanol was more predominant, probably due to the higher injection pressures. Insensitivity to combustion noise was observed, resulting in higher values than the conventional target, in the range of 6-7 dBA in the entire CA50 range considered. Figure 18 shows the effect of holes numbers on thermal and combustion efficiency, indicated specific PM, and CO2 emissions. Figure 16: FSR function of CA50 in \(2000\times 8\) test point, 9 holes vs. 7 holes. Figure 17: Effect of a different nozzle hole number on CA90-10, ID, COV\({}_{\text{IMEP}}\) and combustion noise. Figure 18: Influence of a different nozzle hole number on efficiencies, PM and CO\({}_{2}\) indicated specific emissions.