## 2 Materials and Methods
The signals of injector energizing, injection rate, fuel pressure and back pressure were recorded using an AVL IndiModul 622 data acquisition device. The mass of injected fuel was obtained from the mean value of 1000 continuous injections measured by a precision scale Kern 572-31 (weighing capacity 300 g, \(\pm\)0.005 g). The fuel temperature inside the measurement tube was measured using a Pt100 sensor (measure range \(-\)30\(\rightarrow\)+180 \({}^{\circ}\)C, uncertainty \(\pm\)0.8 \({}^{\circ}\)C) and controlled within a range of \(308\pm 5\,\mathrm{K}\). The injection pressure varied from 24 MPa to 80 MPa and the energizing duration was adjusted to ensure that the same amount of fuel (70 mm\({}^{3}\)) was injected, regardless of the type of fuel (Table 3). The pressure in the measurement tube (back pressure) was adjusted to 4.0 MPa. The results of 100 consecutive injection cycles were recorded and averaged for analysis. The average standard deviation of the injection rate is presented in Table 4.  
Measurements of macroscopic spray characteristics were performed under non-evaporating conditions in a specially designed spray chamber (Figure 2). A medium-pressure stainless steel constant-volume chamber was constructed and produced for this purpose. The chamber had a diameter of 110 mm and was equipped with an optical accessible window. Figure 1: Schematic diagram and photo of the injection rate measuring systems. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Injector Energizing Duration, ms**} \\ \hline
**Injection Pressure** & **DF** & **RO25** & **RO50** & **RO75** & **RO** \\ \hline
24.0 MPa & 2.60 & 2.65 & 2.80 & 3.25 & 3.30 \\ \hline
40.0 MPa & 1.85 & 1.50 & 2.00 & 2.10 & 2.20 \\ \hline
60.0 MPa & 1.35 & 1.40 & 1.45 & 1.55 & 1.70 \\ \hline
80.0 MPa & 1.10 & 1.20 & 1.25 & 1.30 & 1.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Test matrix for injection rate and spray macroscopic characteristics measurement. The spray chamber was filled with inert gas nitrogen (N\({}_{2}\)) from a high-pressure vessel to a constant back pressure of 4.0 MPa, which was controlled with a pressure regulator valve. The temperature inside the spray chamber also was kept at a constant level of 20 \({}^{\circ}\)C to ensure non-evaporating test conditions. After each measurement, the nitrogen was re-placed to reduce the volume of fuel vapors and thus improve visibility through the chamber window. The fuel injection system used in this experiment was similar to that used in the injection rate measurement system. A National Instrument CompactRIO system with a real-time controller and necessary modules has been used to control the system and measure gas parameters. For this purpose, special software in the LabView environment has been designed and used. High-speed video camera PHOTRON FASTCAM-1024 PCI was used to capture images of fuel sprays at capturing speed of 18,000 frames per second. The following measurements were analyzed from the images: spray tip penetration, spray width, and spray cone angle. The surface area was calculated using these resulting measurements. The analysis of images and measurements has been produced by the software NI \"Vision Assistant 2010\". For each mode, the images of 10 injections were analyzed. Spray tip penetration was defined as the distance from the nozzle exit to the furthest point of the spray. The average standard deviation of the spray tip penetration is presented in Table 5. The spray cone angle was