# Investigation of the Behaviors of Methanol Spray Impingement and Wall Wetting
## 3 Results and Discussion  
### Macroscopic Behaviors of Spray Impingement  
Figure 6 illustrated the impinging spray morphology under different impingement distance \(D_{imp}\) (from 62 to 120 mm). When the spray distance was 62 mm, the overall shape of the imping spray was trapezoidal, and gradually changed to rectangular with the increase of spray distance (120 mm). After the spray was injected, the aerodynamic convergence caused by the relative velocity between it and the surrounding gas led to the secondary fragmentation of the droplets, and also produced aerodynamic resistance to the droplets [14; 29], thereby reducing the kinetic energy of spray. The larger the spray distance was, the longer the flight distance spray was, and the energy loss caused by air resistance increased, which slowed down the axial and radial droplet velocity further, causing the deformation of the far end of the spray. As shown in Figure 7, the change of impinging spray height \(H_{i}\) and width \(W_{i}\) of spray underwent two stages. The first stage began at the beginning of spray impinging on the wall. With the continuous process of spray impinging the wall, droplets splashed continuously, and \(H_{i}\) and \(W_{i}\) increased rapidly. The second stage started at the end of  
Figure 5: Calibration equation of the fuel film thickness and the average change of light intensity. Figure 6: The impinging spray morphology under different \(D_{imp}\). the spray impinging the wall. Due to air resistance, the spray diffusion speed gradually decreased, and the growth rate of \(H_{i}\) and \(W_{i}\) decreased significantly. Figure 8 showed the impinging spray morphology under different wall temperature \(T_{wall}\) (from 293 K to 423 K). The three sprays had a similar macro shape with various wall temperature conditions. Figure 9 showed the changes in \(H_{i}\) and \(W_{i}\) with time. When \(T_{wall}\) was 323 K, 373 K, and 423 K, \(H_{i}\) was significantly higher than that of the usual temperature wall before 5 ms ASOI. However, in the following time, the changes of \(H_{i}\) corresponding to different \(T_{wall}\) were similar. Generally, \(H_{i}\) of methanol spray on the wall was positively correlated with \(T_{wall}\). Similarly, \(W_{i}\) was positively correlated with \(T_{wall}\). However, the relative difference between \(W_{i}\) curves of \(T_{wall}\) 373 K and 423 K in a short time after the spray impacted the  
Figure 8: The spray morphology under different \(T_{wall}\). Figure 7: (**a**) Impinging spray height \(H_{i}\) and (**b**) width \(W_{i}\) of impinging spray under different \(D_{imp}\). wall is small. After about 6.5 ms ASOI, the growth rate of \(W_{i}\) was gradually lower when \(T_{mall}\) was 373 K than when \(T_{mall}\) was 423 K. The reason for the above results was that, on the one hand, the density decreased due to the rise of air temperature near the wall, and the resistance to droplet movement decreased to a certain extent; on the other hand, it was the strengthening of spray secondary atomization caused by the hot wall. This was similar to the previous research results of [PERSON] et al. [14]. Figure 10 showed the impinging spray morphology under different injection pressure \(P_{inj}\) (from 300 kPa to 500 kPa). At the same time, after the start of injection, the speed of methanol spray was positively correlated with \(P_{inj}\). Figure 9: **(a)** Impinging spray height \(H_{i}\) and (b) width \(W_{i}\) of impinging spray under different \(T_{null}\). Figure 11 showed the changes of \(H_{i}\) and \(W_{i}\) with time under different \(P_{inj}\). Under a higher injection spray pressure, the impact energy of the droplet was higher, and the splashing behavior was more likely to occur after the impact of the wall. Therefore, both \(H_{i}\) and \(W_{i}\) were positively correlated with \(P_{inj}\). At 15 ms ASOI, the average \(H_{i}\) with the injection pressure of 300 kPa, 400 kPa, and 500 kPa was about 15.0 mm, 15.7 mm, and 16.0 mm, respectively.