## 4 Discussion  
Compiling the test results in graphical form, Figure 10a was obtained. All of the tested injectors showed an increasing trend with an \"inflection\" near the maximum values. The Barracuda 115 injector has the characteristic with the least degree of curvature. The studies presented in the paper are among the first on the subject, so it is difficult to find literature reports for comparison. The only data we can find are the rarely posted information in manufacturers' technical materials. Figure 11a shows the dependence of volumetric flow rate on injector nozzle bore diameter for the Barracuda injector [70] (supply pressure \(p_{air}\) = 1 \(\times\) 10\({}^{5}\) Pa). The difference here is that the injector was continuously open, rather than cycled open at a preset time and frequency as in this study. There are differences in \(Q\) values, but the trend of increments in both cases is preserved. For the other injectors studied, unfortunately, no comparative data was found. In manufacturers' technical materials, information regarding the predicted maximum power \(P_{\max}\) obtainable from one cylinder at different \(d_{on}\) diameters can be found more often than information regarding \(Q\) values. Figure 11b shows the dependence of \(P_{\max}\) on \(d_{on}\) for Barracuda 115 [70] and AC W01-4 [58] injectors (supply pressure \(p_{\mathrm{gss}}\) = 1 \(\times\) 10\({}^{5}\) Pa). Here, too, an upward trend of a comparable nature to the study's results is evident (except for the last point in the case of the AC W01-4 injector). Figure 10: Summary of research results: (**a**) flow characteristic; (**b**) percentage differences to the Matrix HS 211.20 injector. Analyzing the aggregate results shown in Figure 10a, the issue of \(Q\) differences at the same \(d_{on}\) points for different injectors remains to be clarified. Keep in mind that the same supply pressure value (\(p_{air}=1\times 10^{5}\) Pa) and the same \(d_{on}\) hole diameters are the main flow restriction. The highest \(Q\) values were obtained for the Matrix HS 211.20 injector, on average the volumetric flow rate was 17.3% higher than the Barracuda 115 injector and 26.7% higher than the AC-W01-4 injector (Figure 10b). Different injector opening and closing times are seen as a possible reason for the differences in \(Q\) values under the same test conditions for the different injectors. It is uncertain at this point whether the manufacturers (Table 1) meant the same thing by opening and closing times, i.e., whether it includes the response (delay) time or only the opening and closing times. Therefore, it was decided to conduct additional tests to confirm the values of opening and closing times for the tested injectors. The test stand, as mentioned earlier, had the ability to determine these times. The cyclicality of the injector was assumed according to the basic tests, \(t_{imp}=5\) ms,\(f=16.67\) Hz, supply air pressure \(p_{air}=1\times 10^{5}\) Pa, and diameter \(d_{on}=2.9\) mm. Additional equipment included:  
* Oscilloscope RIGOL MSO4014 (bandwidth--100 MHz; real time sample rate--up to 4 GSa/s; vertical resolution--8 bit; frequency--1 kHz);
* Voltage meter RIGOL RP1500A (bandwidth \(\sim\)150 MHz; damping factor--10:1; maximum input voltage--CAT II 300V AC);
* Pressure sensor MPXH6400A (response time \(<1\) ms; range (20... 400) kPa; output signal (0... 5) V; accuracy 0.25%). Measuring the pressure at the outlet of the injector nozzle as an indirect method for evaluating opening and closing times is widely used by manufacturers and, as shown in [49], yields results comparable to direct methods, particularly for opening times. Comparing the results of the additional tests shown in Figure 12 and in Table 6, differences between the injectors are apparent. While the closing times are similar and within (1.64...1.88) ms, the opening times are different. The times quoted by the injector manufacturers (Table 1) also differ from those determined in additional tests (Table 6).