## 3 Results and Discussion
### Effects of the Nozzle Hole Numbers on FSR in the DF Mode
The different nozzle hole number, for \(1500\times 5\), had no influence on the indicated specific PM except for more advanced combustion phasing (4 deg) related to fewer nozzle cases. The abrupt variation observed was due to the lower value of FSR achieved, as shown in Figure 15. For higher load and speed, PM decreased while increasing the ethanol fraction for both nozzle cases. Figure 18 compares engine-out PM emissions between DF and conventional diesel modes. The ethanol addition significantly reduced them in both cases investigated, in particular at 5 bar of BMEP. These benefits were evident by adopting a high FSR because of the reduced quantity of diesel fuel, which reacted with the ethanol-air mixture leading to dominant premixed combustion, with a consequent reduction of PM, in this case of about 95% in the CA50 range considered. An exception at the lowest CA50, for both, tested points, where a lower FSR justified an important difference in terms of soot, of about 90% and 50%, for \(1500\times 5\) and \(2000\times 8\), respectively. No relevant influence could be noticed in both cases for thermal efficiency, while the combustion efficiency decrease was related to the CO/HC trend. Related to this point, further explanations are given below. The effect of different nozzle hole numbers on indicated specific CO and HC emissions are illustrated in Figure 15.0 As can be seen for both test points, the adoption of 9 holes injector led to an increase of HC emissions retarding combustion phasing. The trend was mainly evident at \(2000\times 8\). With more jets, since the same hydraulic flow rate, the amount of diesel per zone in the combustion chamber was lower. So, retarding combustion phasing the unburned fraction increased owing to lower mean in-cylinder temperature, as lower peaks of HRR shown in Figure 15.1 Despite the HC worsening, the combustion efficiency, as shown in Figure 18, maintained acceptable values within the CA50 range considered. For both test points, the CO emissions increased with further increment of ethanol fraction injected, but CO levels decreased increasing the engine load. The high heat of vaporization of ethanol (Table 2) and the consequent cooling effect on the charge reasonably affected the CO oxidation. The CO\({}_{2}\) emissions (Figure 18) strongly depended on CO oxidation. In \(1500\times 5\), the lower mean in-cylinder temperature due to higher FSR reached (Figure 15), did not allow complete oxidation of CO and a lower level of CO\({}_{2}\) emitted could be observed in the whole operating range observed. For a higher load, no relevant differences comparing the CO\({}_{2}\) trend could be noticed due to an improved combustion process and the higher values of combustion efficiency compared with the lower load case are shown in Figure 15.2  
In all cases, as remarked in Figure 19, the ethanol fumigation increased the CO and HC emissions owing to the cooling effect of the ethanol on the combustion process. For both test points, it was also found that the CO\({}_{2}\) emissions were lower compared to the diesel target due to the lower C/H ratio and the worsening of the fuel oxidation to produce CO\({}_{2}\). Figure 15.3 Influence of the different nozzle hole number on indicated CO and HC. It is worth highlighting that the multi-injection pattern used in this analysis was calibrated for 7 holes case. Reasonably, for 9 holes case, a dedicated calibration can reveal further improvements not visible at this stage.