# Investigation of the Behaviors of Methanol Spray Impingement and Wall Wetting
## 3 Results and Discussion
### Fuel Adhesion Formation
The fuel film area \(A_{f}\) basically showed a negative correlation with the wall temperature (Figure 16a), but the trend of \(A_{f}\) corresponding to 373 K and 423 K \(T_{wall}\) was almost the same, which was caused by that part of the adhesive fuel extending outward at the edge and droplets settling at the periphery of the liquid film area where it evaporated quickly with higher \(T_{wall}\). As shown in Figure 16b, film thickness \(T_{f}\) showed the non-monotonical behaviors versus wall temperature \(T_{wall}\) say between 293 K-373 K, \(T_{f}\) had a negative correlation with \(T_{wall}\), but for \(T_{wall}\) of 423 K, \(T_{f}\) was the largest of the four temperature conditions. Combined with the boiling phenomenon mentioned above at 423 K, it indicated that the non-monotonical trend was a result of the competition between a higher plate droplet temperature difference and a lower heat convection coefficient caused by partial film boiling. When the wall temperature rose above the critical value (here, the critical value was between 373 K and 423 K), although the increase of wall temperature and droplet temperature difference increased the evaporation rate, the effect of the decrease of heat transfer coefficient caused by partial film boiling at this time was more significant, which reduced the actual evaporation rate. Figure 14: (**a**) Fuel film area \(A_{f}\), (**b**) Fuel film thickness \(T_{f}\) and (**c**) Fuel film mass \(M_{f}\) on the wall with temperature 293 K under different \(D_{imp}\). The adhesive fuel mass \(M_{f}\) was mainly affected by the evaporation rate of methanol and the settling rate of atomized droplets in the air. As shown in Figure 16c, for the case of 293 K \(T_{wall}\), the evaporation rate of droplets was lower than the sedimentation rate of atomized droplets in the air, so the quality of the liquid film was constantly rising. \(M_{f}\) at \(T_{wall}\) of 323 K and 373 K did not change significantly with time, indicating that the evaporation rate of methanol was the same as the sedimentation rate of droplets. These two factors offset each other to a certain extent. After \(T_{wall}\) further increased to 423 K, \(M_{f}\) began to rise slowly with time, indicating that under this working condition, the promotion effect of wall temperature on secondary crushing was slightly greater than that on methanol evaporation. In addition, \(M_{f}\) was negatively correlated with the wall temperature from 293-373 K. However, when \(T_{wall}\) further rose to 423 K, the corresponding \(M_{f}\) was greater than that under 373 K \(T_{wall}\) at the same ASOI time. The main reason for this phenomenon was that adhesive fuel after the methanol spray impacted the wall temporarily underwent partial film boiling. Compared with the nuclear boiling under \(T_{wall}\) of 373 K, the droplets  
Figure 16: (a) Fuel film area \(A_{f}\), (b) Fuel film thickness \(T_{f}\) and (c) Fuel film mass \(M_{f}\) on the wall under different \(T_{wall}\). Figure 15: Pseudo color images of fuel film on the wall under different \(T_{wall}\). were separated from the wall by a vapor layer (the 'Leidenfrost' effect), resulting in the reduction of methanol vaporization efficiency during this time. Figure 17 showed the pseudo color images of fuel adhesion formation under different injection pressure \(P_{inj}\). Figure 18 gave the time-dependent curves of \(A_{f}\), \(T_{f}\) and \(M_{f}\) obtained from image analysis. Similar to results of pseudo color images, the two working conditions of 400 kPa \(P_{inj}\) and 500 kPa \(P_{inj}\) showed similar change of \(A_{f}\) within the studied time range (Figure 18a), however, when \(P_{inj}\) was 300 kPa, \(A_{f}\) was significantly lower than that of the other conditions. Compared with \(P_{inj}\) of 300 kPa, \(T_{f}\) (Figure 18b) and \(M_{f}\) (Figure 18c) at \(P_{inj}\) of 400 kPa increased.