# Impacts of Micro-Deviations of Aperture on the Characteristics of Collision Atomization Field
## 5 Results and Discussion
### Influence of Colliding Aperture Deviation on Atomization Effect
In the 4% deviation orifice with a diameter of 1 mm as the standard, from the initial pressure of 0.2 MPa to the hydraulic turnover, the volume flow rate increases by nearly 30 L/h at most and 21.7 L/h at least. When the injection pressure increases to 0.8 MPa after hydraulic turnover, the volume flow rate generally increases by only approximately 20 L/h. Figure 11 also shows that for the orifice with diameter deviation, the larger the aperture is, the greater the flow of the nozzle is. The nozzle with negative deviation (0.95-1.00 mm) is easier to reach the state of hydraulic turnover than the nozzle with positive deviation, which also illustrates that the smaller aperture nozzles can bear less pressure. The relationship between the discharge coefficient \(C_{d}\) and cavitation number \(K\) of single side small deviation cylindrical nozzles is depicted in Figure 12. The variation characteristics of \(C_{d}\) show a great difference with the increase in \(K\) before and after hydraulic turnover. Before the hydraulic turnover, for a specific orifice, when the injection pressure gradually increases, the influence of the viscous resistance on the liquid movement in the orifice inner wall will decrease, which leads to the monotonic increase in \(C_{d}\) with the decrease in \(K\). When hydraulic overturning occurs, due to the generation and development of cavitation, the flow in the orifice decreases rapidly, resulting in a significant reduction in the discharge coefficient. After hydraulic turnover, because a layer of gas membrane is attached to the inner wall of the nozzle, the viscous resistance is greatly reduced and the flow coefficient increases again. For the nozzle with diameter deviation, the larger the forward deviation, the lower the \(C_{d}\) corresponding to the nozzle, which is directly related to the outlet area of the nozzle, and the larger the area, the lower the flow rate. It can also be seen from the curves of multiple orifices that the inflection point of each curve changes regularly. The smaller the nozzle, the larger the corresponding inflection point. The inflection point of each curve is the critical point for the emergence and end of hydraulic pressure. This also implies that a small orifice requires less injection pressure, and vice versa. It can be concluded from Figure 12 that the increase in the orifice diameter (positive deviation) reduces the flow coefficient and the curve inflection point gradually moves to the left and down, making cavitation and hydraulic overturning more difficult to occur. On the contrary, the decrease in the orifice diameter (negative deviation) increases the flow coefficient, and cavitation and hydraulic turnover will occur earlier with the increase in injection pressure. Figure 12: Relationship between the discharge coefficient and cavitation number of single small deviation cylindrical nozzles. Figure 13 is the SMD curve of different injection pressures and small range of impact nozzle diameter change. Among them, Figure 13a shows the relationship between SMD and collision aperture under different injection pressures. Figure 13b is the curve of SMD with injection pressure for collision aperture with 5% deviation based on 1.00 mm. It is obvious from Figure 13a that SMD increases with the increase in the diameter of the impinging nozzle. Under the same injection pressure, the increase in the nozzle diameter leads to the weakening of the cavitation in the internal flow field, the softer collision between the two jets, the insufficient atomization in the atomization field and the larger SMD. When the diameter of impinging nozzle varies in the range of 0.95-1.05 mm, the variation range of SMD becomes smaller and smaller with the increase in injection pressure. In addition, for a fixed orifice diameter, SMD tends to decrease with the increase in injection pressure, and the decreasing range gradually becomes smaller, and finally tends to a stable SMD value.