## 3 Results and Discussion
### Analysis of Fuel Ignition and Combustion
2.2 Analysis of the Fuel Droplet Ignition and Combustion Characteristics under a Conductive Heat Supply  
In the conducted experiments on the ignition and combustion of fuel droplets under a conductive heat supply from the heating surface, the nominal operating conditions of boiler units were reproduced. In the combustion chambers of boiler units, fuel droplets collide with internal surfaces heated to high temperatures. Based on the experimental results, we conducted an analysis of the influence of the texture configuration formed on steel surfaces by laser radiation on the ignition (\(\tau_{d}\)) (Figure 9) and combustion (\(N\), \(D_{\text{max}}\), and \(\tau_{\text{burn}}\)) (Figure 10) characteristics of fuel droplets (oil, emulsion, and slurry). Figure 8: 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 mixed heat supply. It can be seen in Figure 9 that in the case of a mixed heat supply, laser processing of steel surfaces helps to reduce the ignition delay time under a conductive heat supply. For example, \(\tau_{d}\) of a suspension droplet on the 2 AB surface is 40% less than that on the polished surface P (Figure 9). It was found that the texture configuration has a significant effect on the ignition and combustion characteristics (Figure 9). Among the texture configurations used in the experiments, the shortest ignition delay times for oil droplets, emulsions, and slurries were recorded on the 2 AB surface, all other conditions being equal. On the 2 AB surface, the area of the regions unprocessed by laser radiation is twice the area of the regions processed by laser radiation. Since the deposition of metal vapors and crystallization of melt material occurs on unprocessed regions (Figure 6d), these regions are characterized by significant roughness and a developed hierarchical multimodal texture. This is the cause of a significant increase in the surface area of regions unprocessed by laser radiation due to roughness (formed texture). Under the conditions of the experiment, a vapor layer (the evaporated products that make up the fuel) was formed between a fuel droplet and the steel surface. Despite the fact that heat from the heating surface to the fuel droplet is transferred through a vapor layer, the intensity of heat transfer from the 2 AB surface to the droplet was higher than on the P, AB, and A2B surfaces. This is due to the fact that the 2 AB surface has the largest surface area among the surfaces used in the experiment. The higher the intensity of heat transfer from the surface to the fuel droplet, the higher the evaporation intensity of the combustible components that make up the fuel. As a result, the necessary concentration of combustible substances is formed near the droplet for a shorter period of time for the implementation of gas-phase ignition. For these reasons, the ignition delay times of fuels on the AB surfaces are smaller. The effect of the increase in surface area on the ignition characteristics is especially noticeable when comparing the results obtained using the AB and A2B surfaces. In contrast to the conditions of a mixed heat supply (Figure 7),  
Figure 9: Ignition delay times of fuel droplets (liquid oil in the usual state, emulsion, and slurry) under a conductive heat supply. fuel droplets on the AB texture configuration under a conductive heat supply ignited faster than on the A2B texture configuration, all other conditions being equal. The reason for this can only be a larger increase in the surface area due to the roughness on the A2B surface (Table 2) since the contact diameter of the droplets in all experiments with a conductive heat supply was constant (limited by the size of a special holder).