## 5 Conclusions  
Although transportation is increasingly using electric and hybrid propulsion, internal combustion engines are still the main source of propulsion. The use of alternative carpower systems, particularly LPG, is cited as one method that promotes reductions in toxic emissions and fuel costs. In this type of system, the executive element responsible for fuel dosage is the low-pressure gas-phase injector. If the conversion of an internal combustion engine to gas power indicates the need to increase the diameter of the outlet nozzle bore, it is important to know the flow characteristics with respect to this variable. Injector manufacturers present such characteristics for a continuously open injector, which is not practical, since the injector cycles at a certain frequency and time of opening. Therefore, which is new, it was decided to determine the flow characteristics of structurally different injectors operating at a certain frequency and time of opening depending on the diameter of the nozzle bore. Based on the research and analysis carried out, it was found out that: \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**AC W01-4**} & \multicolumn{2}{c}{**Barracuda 115**} & \multicolumn{2}{c}{**Matrix HS 211.20**} \\ \cline{2-7}  & **Manuf.** & **Measur.** & **Manuf.** & **Measure.** & **Manuf.** & **Measur.** \\ \hline Opening time & 2.30 ms & 2.43 ms & 1.90 ms & 2.18 ms & 1.00 ms & 1.54 ms \\ Closing time & 1.40 ms & 1.88 ms & 1.20 ms & 1.68 ms & 1.00 ms & 1.64 ms \\ Cycle mean pressure & \(1.911\times 10^{4}\) Pa & \multicolumn{2}{c}{2.089 \(\times\) 10\({}^{4}\) Pa} & \multicolumn{2}{c}{\(1.878\times 10^{4}\) Pa} \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison of injector opening and closing times determined from additional tests with manufacturers’ data from Table 1 and cycle mean pressure. Figure 12: Pressure waveforms at the outlet of the injector nozzle as a response to the control impulse. * There are discrepancies in the flow characteristics of the tested injectors at the same diameters of the outlet nozzle bores;
* Flow characteristics can be successfully fitted by a second-degree polynomial obtaining high-quality values. * Highest volumetric flow rate values were obtained for the Matrix HS 211.20 injector; on average, it was 19.6% higher than the Barracuda 115 injector and 35.8% higher than the AC-W01-4 injector;
* Shortest opening time (calculated from the beginning of the control pulse) was obtained for the Matrix HS 211.20 injector and was 1.54 ms; the Barracuda 115 injector's time was longer by 29.3% (2.18 ms), while the AC W01-4 injector's time was longer by 36.6% (2.45 ms);
* The closing times of the tested injectors (calculated from the control pulse fade) were very similar (1.64...1.88) ms;
* Injector nozzle outlet pressure waveforms showed lower values for the Matrix HS 211.20 injector, which translated into lower average cycle pressure; the AC W01-4 injector's pressure was 1.8% higher, and the Barracuda 115 injector's one was 9.94% higher;
* Studies of opening and closing times and nozzle outlet pressure waveforms allowed an indirect explanation of the differences in volumetric flow rate of the tested injectors when using nozzles with the same bore diameter. In the next stage, it is planned to continue research on the determination of flow characteristics with different variables, such as supply pressure and actuator stroke. **Author Contributions:** [PERSON] and [PERSON] supervised all the analyses, conceptualized the article, participated in the research and wrote the paper; [PERSON] and [PERSON] compiled the literature review, performed the analysis, and performed the re-review and editing and formal analysis. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received no external funding. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.