# Investigation of the Behaviors of Methanol Spray Impingement and Wall Wetting
## 1 Introduction  
There are many physical behaviors involved in the process of spray impingement, and its complexity brings great challenges to experimental measurement and numerical simulation. Relevant research started in the 1980s. Due to the limitations of experimental methods and measuring equipment, early tests were inadequate to accurately study high transient processes. Recently, the improvement of optical measurement technology has played a major role in the study of the coupling between spray and wall. At present, the research on spray wall coupling mainly focuses on the following two aspects. First, the research on the dynamic behavior of spray after hitting the wall is constantly being improved [1]. [PERSON] et al. [2] obtained the mathematical relationship between the height and width of the diesel impinging spray and time, environmental density, and the injection pressure. [PERSON] et al. [3] studied the detailed structure of diesel spray when it impacts the normal temperature wall (20 \({}^{\circ}\)C) and heated wall (150 \({}^{\circ}\)C), and they found that higher wall temperature reduced the accumulation of droplets in front of the wall jet, and enhanced the vortex in front of the wall jet. In addition, [PERSON] et al. [4] found that the increase of environmental density will also enhance the vortex in the front of the spray. [PERSON] et al. [5] used isooctane instead of gasoline to study the spray wall impact characteristics of a single-hole low-pressure injector. The results showed that the impact height of spray decreased with the increase of the normal angle between the injector and the wall. [PERSON] et al. [6] used the Mie scattering method and shadow method to study the wall impact characteristics of spray from an in-cylinder direct injection nozzle under different injection angles; they found that reducing the angle with the wall can promote the movement of liquid mist along the wall. [PERSON] et al. [7, 8] studied the wall impactcharacteristics of isooctane spray, and the results showed that the impact height of the gas phase and liquid phase did not increase linearly with the rise of wall temperature, but decreased after exceeding 473 K; they believe that this situation may be related to the \"Leidenfrost\" effect. [PERSON] et al. [9] used a GDI nozzle to inject gasoline onto pistons with different temperatures and found that the increase of piston temperature led to the reduction of the liquid phase, and higher injection pressure improved fuel evaporation. [PERSON] et al. also carried out a spray wall impact experiment using a GDI nozzle [10, 11, 12]. In their experiment, toluene was used as the spray liquid, and the effects of spray pressure, ambient temperature, and density were studied. [PERSON] et al. [13] studied the spray wall impact process of n-butanol/diesel blended fuel. The results showed that the impact height and impact width of spray will decrease with the increase of ambient temperature, ambient pressure, and injection distance, but will increase with the increase of fuel temperature. [PERSON] et al. [14] studied the influence of cross-flow velocity on the wall impact characteristics of the spray, and the results showed that the increase of cross-flow velocity would strengthen the dispersion of spray along the flow direction. Second, the research on the influence of various boundary conditions on fuel wall attachment is being continuously developed. At present, the common measurement methods of the adhered fuel include the weighing method and optical method. [PERSON] et al. [15, 16, 17, 18] carried out a series of studies on the adhered fuel by using the weighing method. The results showed that larger spray distance, higher spray pressure, or higher ambient pressure will lead to the reduction of the adhesive fuel film mass. [PERSON] et al. [19] also used the weighing method to study the fuel adhesion formation of a variety of diesel blended fuels after impinging the wall.