# Experimental Investigation on a Throttleable Pintle-Centrifugal Injector
## 3 Experimental Investigation on the Pintle-Centrifugal Injector
### Results and Discussion
#### 3.3.2 Analysis of Flow Field States  
Figure 8 shows the injection flow field at different strokes for the same flow rate of 181.6 g/s in the test of Injector 1. Due to mechanical problems with the throttleable pintle-centrifugal, the eccentricity of the jet field appears after assembly. However, this eccentricity allows the centrifugal phenomenon to be better observed. Even in the case of the pintle bolt stroke \(s=0.078\) mm, the throttleable pintle-centrifugal injector jet flow field still has a clear rotational motion.  
As can be seen from the figure, when the pintle cone stroke \(s=0.89\)mm, along the injector axially from top to bottom, deionized water in the injection annulus exit formed a clear liquid film, the liquid film in the action of aerodynamic forces appear folded phenomenon and rupture the formation of liquid filaments, and then the liquid filaments continue to form droplets under the action of aerodynamic forces, droplets gradually become smaller droplets. The droplet size varies significantly in the radial direction. This phenomenon is partly due to the uneven flow distribution caused by the eccentricity phenomenon and partly due to the radial distribution of the droplet diameter caused by  
Figure 7: Relationship between injection pressure drop and pintle stroke (Injector 2).  
the aerodynamic force. With the increase in pintle stroke, the axial jet velocity of deionized water gradually decreases, and the deionized water momentum becomes smaller making the obvious effect of aerodynamic force gradually in advance. The occurrence of liquid film folds gradually progresses upwards in the direction of the injector axis, with the droplets becoming progressively smaller and the atomization cone angle gradually increasing at the same axial position. For hybrid rocket motors, the progressive increase in propellant injection atomization cone angle represents the distribution of liquid oxidizer closer to the inner surface of the solid fuel column. During the operation of a hybrid rocket motor, the pintle stroke of the throttleable pintle-centrifugal injector needs to be adjusted appropriately. This aims to improve the ignition speed and combustion performance of the hybrid rocket motor under different oxidant mass flow rates and different cyclonic flow rates.  
A comparable phenomenon is observed in the tests conducted with Injector 2, wherein the liquid film formed by Injector 2 is of shorter duration at the corresponding needle bolus stroke, and the media atomization occurs at an earlier stage, as illustrated in Figure 9. This is attributable to the reduction in the diameter of the tangential holes, which permits the water to swirl at a greater rate subsequent to passing through the tangential holes. In different application scenarios, the use of varying tangential hole sizes can facilitate the regulation of the core area of atomization.  
Figure 8: Flow field at different pintle strokes (Injector 1, \(t=1.00\) s).  
Figure 9: Flow field at different pintle strokes (Injector 2, \(t=1.00\) s).