## 3 Results
### Liquid Hydrocarbons
#### 3.3.2 Spray  
Changes in the droplet velocity values were recorded along the flow. The droplet velocity decreases in four cross-sections of the jet at distances of 25 mm, 50 mm, 75 mm,  
Figure 9: TG and DTG curves for evaporation and thermal decomposition of liquid hydrocarbon samples. Medium—argon 150 ml/min, heating rate—10 \({}^{\circ}\)C/min, sample weight \(\approx\) 15 mg.  
and 100 mm from the nozzle. In this case, the highest droplet velocity values are found directly in the center of the jet (along the axial coordinate). Jet expansion and aerodynamic resistance [49], coagulation of droplets [50], and their rotation and destruction [28] cause changes, such as decreased velocities of liquid droplets along the axial coordinate during spraying. In this case, the trajectory of motion of the liquid hydrocarbon droplets in the jet changes, thus increasing the diameter of the sprayed fuel jet.  
Figure 10 shows an approximation curve of the change in the fuel droplet velocity along the longitudinal axis.  
The experimental results (Figure 10) showed a decrease by no more than 10% in the velocity of liquid hydrocarbon droplets at \(\mathrm{P_{f}/P_{a}}=0.30/0.28\) MPa after spraying. The obtained approximation equation estimates the change in the velocities of fuel droplets as they move away from the sprayer. In addition, Figure 10 shows the droplet sizes and their number in the characteristic sections of the jet. The experimental results showed that 200-400 \(\upmu\)m fuel droplets predominate in the immediate vicinity of the nozzle (at a distance of 25 mm). Their number attains 35% of the total. In this case, the jet contains rather large droplets (more than 600 \(\upmu\)m). The droplet velocity decreases as the distance from the nozzle increases. The sizes of fuel droplets also change due to the aerodynamic resistance of the environment (air). Thus, at a distance of 50 mm from the nozzle, the number of droplets up to 200 \(\upmu\)m and 200-400 \(\upmu\)m in size increases by 3 and 6%, respectively. At the boundary of the study area (100 mm from the nozzle), the number of small droplets (no more than 400 \(\upmu\)m) increases by 16% compared to that in the 25 mm section.  
The droplets of liquid hydrocarbons collide with each other after spraying and form new fragments or retain their integrity. The destruction of rather large droplets depends on the density ratio of air-to-liquid hydrocarbon [51]. High values of the ratio facilitate the droplet deformation and its subsequent destruction. It is known [50] that the smaller changes in droplets dimensions occur for a more viscous liquid. These droplets swirl and transform due to stretching and compression. Therefore, no further destruction occurs since the droplets are spherical and cannot be separated into smaller parts. Thus, the number of large droplets is likely to increase.  
Figure 11 shows a micrograph illustrating the results of the high-speed recording of changes in the jet spraying angle of liquid hydrocarbons. In the image, the jet spraying angle is represented by red lines that indicate the jet boundaries. It is known [52] that spatial distribution of droplets and their size depend on geometric characteristics of the jet, including the spraying angle, which affects the conditions of ignition and combustion of sprayed fuels in the boiler furnaces.  
Figure 10: Change in the velocity of liquid hydrocarbon droplets along the longitudinal axis.  
The experimental value of the jet spraying angle in the study area did not exceed 25\({}^{\circ}\). It should be noted that this value is significantly affected by the liquid parameters (viscosity, density, range). For instance, the jet range grows as the sprayed liquid density increases [53], whereas the stability of fuel droplets deteriorates and they become more susceptible to destruction as dynamic viscosity decreases [54]. As a result, the number of small droplets increases, which greatly simplifies their further ignition.