## 3 Results
### Liquid Hydrocarbons
#### 3.3.3 Ignition and Combustion  
Figure 12 presents the dependences of the change in the ignition delay time and the flame combustion process of single droplets of the liquid hydrocarbon sample on the air temperature (T\({}_{\rm g}\) = 450-700 \({}^{\circ}\)C). The maximum value of the ignition delay time for the liquid hydrocarbon sample was recorded at T\({}_{\rm g}\) = 450 \({}^{\circ}\)C. At increased air temperature (from 450 \({}^{\circ}\)C to 700 \({}^{\circ}\)C), the  
Figure 11: The jet spraying angle of liquid hydrocarbons. Figure 12: Dependences of the ignition delay and flame combustion time of single droplets of the liquid hydrocarbon sample on the air temperature of 450–700 \({}^{\circ}\)C.  
ignition delay time decreased from 19.2 to 1.1 s and exhibited an exponential dependence, which agrees with the results obtained by other authors [55]. It should be noted that at the air temperature ranging from 450 to 550 \({}^{\circ}\)C, the t\({}_{\text{i}}\) parameter was observed to decrease more intensively. This may be due to the intensification of vaporization and release of combustible products that induce the gas-phase ignition of the droplet. Starting from T\({}_{\text{g}}\) = 600 \({}^{\circ}\)C, the dynamics of the relative change in the ignition delay time was observed to decrease. At increased T\({}_{\text{g}}\), the combustion time of a single liquid hydrocarbon droplet in the flaming mode, the formation of which was recorded at T\({}_{\text{g}}\) = 500-700 \({}^{\circ}\)C, tends to increase. A sharp increase in the air temperature leads to this effect, which can be explained by the coking of the droplet surface. It hinders the diffusion interaction between the air and the combustible components of liquid hydrocarbons. The obtained dependence of the flame combustion time of liquid hydrocarbons on the increased air temperature agrees with the data reported by other research [19]. Figure 13 presents the results of high-speed video recording (video frames) illustrating ignition and combustion of single hydrocarbon droplets at T\({}_{\text{g}}\) = 700 \({}^{\circ}\)C (Video S1). The process of droplet ignition and the combustion of liquid hydrocarbons yielded by steam pyrolysis of OS can be divided into several stages. Stage I involved the inert heating of a single droplet. Stage II showed the processes of intense evaporation, formation of volatiles, and the creation of a mixture of combustible gases. Stage III included an intense chemical interaction between combustible components and an oxidizer in a high-temperature gaseous medium. Stage IV involved the heterogeneous combustion of the carbon residue. During the inert heating (Stage I), the droplet changes in appearance (transition to a matte color) and size along its longitudinal and cross sections, which is due to evaporation of light components of hydrocarbons from the near-surface layers. After inert heating, a vapor cloud with a combustible mixture is formed around the droplet surface (Stage II). The gas-phase ignition of the mixture (Stage III) occurs when the minimum required concentration of hydrocarbon vapors is attained at the appropriate temperature. After the gas-phase ignition, a flame was observed to gradually develop around the drop, the surface of which changed significantly (Figure 13). This may indicate the primary evaporation of the fuel (light hydrocarbons) from the droplet surface and the subsequent concentration of heavier fuel components, which makes the droplet shell more viscous [56]. An exception was the droplet combustion at the air temperature of 450 \({}^{\circ}\)C, which proceeded without the formation of a visible flame in the oxidation (smoldering) mode. The flame formation was recorded at T\({}_{\text{g}}\) = 500 \({}^{\circ}\)C.  
The droplet combustion is accompanied by periodic microexplosions and, as a consequence, the deformation of its surface with the separation of smaller fragments (combanions) with a size not exceeding 0.2 mm.