## 3 Results and Discussion
### Analysis of Fuel Ignition and Combustion
Based on the results obtained, it can be concluded that when power-generating equipment operates in the nominal mode, in order to reduce the ignition time of oil droplets in a liquid state, emulsion, and slurry, it is necessary to create a developed multimodal roughness on the heating surfaces characterized by the largest growth of the surface area. The laser technology for processing heating surfaces made of X16 CrNi25-20 steel makes it possible to create a texture in the form of microchannels with specified geometric dimensions and to control the roughness over a fairly wide range of 3D parameters. In this case, it is possible to increase the area of heating surfaces by more than two times due to the creation of microchannels and the developed multimodal roughness consisting of elements of crystallized melt. An increase in the surface area due to roughness makes it possible to  
Figure 10: The number of puffing initiations (**a**), the maximum size of the burnout region (**b**), and the time of complete burnout (**c**) of liquid fuels under a conductive heat supply to the P, AB, A2B, and 2 AB heating surfaces. reduce the ignition delay time of droplets of composite fuels (slurries and emulsions), as well as liquid fuels by up to 40% under the conditions of operation of power-generating equipment in the nominal mode. Figure 10 shows the combustion characteristics of liquid fuels on steel surfaces, including the number of puffing initiations (Figure 10a), the maximum size of the burnout region (Figure 10b), and the burnout time of fuel droplets (Figure 10c). It can be seen in Figure 10c that among the texture configurations used in the experiments, the shortest burnout time for droplets of oil, emulsion, and slurry fuels was recorded on the 2 AB surfaces, all other conditions being equal. The result obtained, as well as the above-established conclusions, is explained by a more developed surface due to the selected texture configuration. Thus, the decrease in burnout times on the 2 AB surface compared to the polished surface, in the case of combustion of oil droplets, is more than 40%, in the case of emulsion it is 40%, and in the case of slurry it is 34%. In addition, the texture configuration also affects other basic combustion characteristics, such as the maximum size of the burnout region (Figure 10a). In the case of burning emulsion and slurry droplets, which include water in addition to combustible components, the texture also affects the number of puffing initiations (Figure 10b). It is fairly well known [37; 38; 39] that puffing is caused by the multicomponent fuel composition, which necessarily includes two mutually insoluble liquid components. Among the considered texture configurations, the 2 AB surface is characterized by the most developed roughness (Table 2). The higher the surface roughness, the more stable nucleation centers on it. For this reason, the number of puffing initiations during the combustion of emulsion and slurry droplets on the 2 AB surface is greater than on the AB and A2B surfaces. For oil droplets in the usual state, there is no secondary atomization during combustion; for this reason, it is not presented in Figure 10a. An increase in the number of puffing initiations intensifies the combustion process by increasing the burnout region. This is illustrated by the established dependencies in Figure 10b. In addition, the dependencies in Figure 10b demonstrate the effect of the developed texture on the increase in the maximum size of the burnout region of fuel droplets (oil in the usual liquid state) burning without secondary atomization. It was found that it is possible to increase the size of the fuel droplet burnout region by 65% (the largest increase in \(D_{\text{max}}\) was recorded in the case of oil droplet combustion on the 2 AB surface compared to combustion on the P surface) due to the developed texture.