## 3 Results
### Storage Tank Pressure Optimization  
After 24 h of monitoring, the compressor was activated four times to refill LP, twelve times for MP, and twenty-four times for HP. A total of 218 vehicle tanks were filled, with an average mass of 9.46 kg per tank. The work performed by the compressor for compression was calculated as 0.1938 kWh per unit mass. These results indicate that optimizing the selected pressures and volumes of the storage tanks can enhance refueling efficiency. To achieve this, the Taguchi design method  
Figure 11: Temperature and mass flow rate changes during filling of the first three vehicle tanks. Figure 10: Pressure changes during cascade storage and in vehicle tanks. was used to analyze the pressure and volume ratios that maximize the number of vehicle tanks filled and the total mass delivered while minimizing compressor operation. The control factors and levels used in the analysis are presented in Table 4. In the Taguchi design, three control factors were selected to determine storage tank pressures: high storage tank pressure (P\({}_{\text{high}}\)), medium storage tank pressure (P\({}_{\text{medium}}\)), and low storage tank pressure (P\({}_{\text{low}}\)). Each factor had four levels (4\({}^{3}\) combinations). The control factor levels were assigned according to the L16 orthogonal array. For these 16 test cases, the number of vehicle tanks filled in 24 h (n\({}_{\text{Vehicle}}\)), the average mass of gas accumulated in each vehicle tank (m\({}_{\text{average}}\)), and the work performed by the compressor per unit mass (W\({}_{\text{comp}}\)) were calculated. The results are summarized under the \"Results\" column in Table 6.  
Using Minitab software, signal-to-noise (S/N) ratios were computed. The \"larger is better\" approach was applied to n\({}_{\text{Vehicle}}\) and m\({}_{\text{average}}\), while the \"smaller is better\" approach was used for W\({}_{\text{comp}}\). The calculated S/N ratio values for each output parameter are also provided in Table 6.  
Figure 12a illustrates the calculated S/N ratios for n\({}_{\text{Vehicle}}\) at specified control factor levels. Optimal performance is achieved by selecting the level that maximizes the S/N value for each factor. The highest n\({}_{\text{Vehicle}}\) value of 229 occurs when the HP pressure (P\({}_{\text{high}}\)) is set to 250 bar, the MP pressure (P\({}_{\text{medium}}\)) to 145 bar, and the LP pressure (P\({}_{\text{low}}\)) to 70 bar. Figure 12b presents the S/N ratios of control factors for the average gas mass (m\({}_{\text{Average}}\)) accumulated in the vehicle tank. The highest m\({}_{\text{average}}\) value of 9.43 kg is obtained when P\({}_{\text{high}}\) is 250 bar, P\({}_{\text{medium}}\) is 205 bar, and P\({}_{\text{low}}\) is 90 bar. At 130 bar (P\({}_{\text{low}}\)), which is the second-best option, m\({}_{\text{Average}}\) is calculated as 9.46 kg. Figure 13 displays the graphical S/N ratios of control factors for the work performed by the compressor per unit mass filled (W\({}_{\text{Comp}}\)). The lowest W\({}_{\text{Comp}}\) value of 0.1898 kWh/kg is achieved when P\({}_{\text{high}}\) is set to 220 bar, P\({}_{\text{medium}}\) to 145 bar, and P\({}_{\text{low}}\) to 90 bar, which correspond to the levels yielding the maximum S/N ratio. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Control Factors and Levels**} & \multicolumn{3}{c}{**Results**} & \multicolumn{3}{c}{**S/N Ratio**} \\ \hline
**Sim. No** & \begin{tabular}{c} **P\({}_{\text{high}}\)** \\ **[Bar]** \\ \end{tabular}  & \begin{tabular}{c} **P\({}_{\text{medium}}\)** \\ **[Bar]** \\ \end{tabular}  & \begin{tabular}{c} **P\({}_{\text{low}}\)** \\ **[Bar]** \\ \end{tabular}  & **n\({}_{\text{Vehicle}}\)** & \begin{tabular}{c} **m\({}_{\text{Average}}\)** \\ **[kg]** \\ \end{tabular}  & \begin{tabular}{c} **W\({}_{\text{Comp}}\)** \\ **[kWh/kg]** \\ \end{tabular}  & **n\({}_{\text{Vehicle}}\)** & \ \begin{tabular}{c} **m\({}_{\text{Average}}\)** \\ **[kg]** \\ \end{tabular}  &