# Experimental Investigation on a Throttleable Pintle-Centrifugal Injector
## 3 Experimental Investigation on the Pintle-Centrifugal Injector
### Results and Discussion  
#### 3.3.1 Analysis of Injection Pressure Drop  
Flow tests were carried out for the throttleable pintle-centrifugal Injector 1 in the deionized water mass flow range 57.3-392.7 g/s. The pressure drop was measured using a piezoresistive pressure sensor (\(\pm\)0.25% FS) at pressure taps located in the fluid collecting cavity, as shown in Figure 1. This pressure governs the propellant's exit velocity, a key metric for injector evaluation, ensuring stable injection and enhanced atomization. The injection pressure drop of the injector was adjusted by varying the pintle stroke at different mass flow rates. The relationship between the injection pressure drop and the pintle stroke at different mass flow rates is shown in Figure 6. The pressure drop measurements were recorded with a pressure sensor accurate to \(\pm\)0.25% of full scale. Given the high precision of the sensor, the uncertainty in the measurements has a minimal impact on the experimental  
Figure 5: Propellant delivery system. data. The accuracy of the sensor ensures that the recorded pressure drops are reliable, and the effect of measurement uncertainty on the overall results is negligible. As can be seen from the figure, as the pintle stroke increases, the injection pressure drop of the adjustable centrifugal injector decreases. When the pintle stroke gradually increases from 0, the injection pressure drop decreases at a faster rate. As the pintle stroke gradually increases, the rate of reduction in the injection pressure drop slows down. When the pintle stroke increases to a certain value, the injection pressure drop tends to stabilize. The pressure drop, measured in the fluid collecting cavity upstream of the tangential holes (\(D_{t}\)) via a piezoresistive sensor (\(\pm\)0.25% FS, Figure 1), is defined as the difference between cavity pressure and ambient pressure at the injector outlet, where the medium is discharged. This drop reflects the cumulative throttling effects of the tangential holes and the annular slit (formed by \(D_{a}\) and \(D_{inj}\)), which sequentially serve as the minimum cross-sectional area. When the slit area (adjusted by pintle stroke, \(s\)) is less than the total area of the tangential holes, the slit dominates the drop; when it exceeds this, the holes become the primary restriction, as evidenced by the stabilizing pressure drop at higher s values (Figure 6). In addition, as the mass flow rate of deionized water increases, the effective range of pintle stroke control gradually increases. At a deionized water mass flow rate of 57.4 g/s, the pintle stroke is no longer able to regulate the injection pressure drop of the adjustable centrifugal injector after 0.4 mm. At a deionized water flow rate of 392.7 g/s, the pintle stroke of 1.0 mm still regulates the injection pressure drop of the adjustable centrifugal injector. At a deionized water mass flow rate of 57.4 g/s and a pintle opening of 0.072 mm, the throttleable pintle-centrifugal injector achieved an injection pressure drop of 0.0697 MPa. At a deionized water mass flow rate of 392.7 g/s and a pintle opening of 0.953 mm, the throttleable pintle-centrifugal injector achieved an injection pressure drop of 0.2901 MPa. For comparison, with a deionized water mass flow rate adjustment ratio of 6.841, the throttleable pintle-centrifugal injector achieves an injection pressure drop variation ratio of 4.162 through the adjustment of the pintle stroke. Although the 4.162 pressure drop ratio achieved at this flow rate variation does not necessarily guarantee effective atomization of the throttleable pintle-centrifugal injector. However, it is possible to achieve effective atomization of the throttleable pintle-centrifugal injector with less variation in injection pressure drop by means of a reasonable adjustment of the pintle stroke. Figure 6: Relationship between injection pressure drop and pintle stroke (Injector 1).