## 3 Results and Discussion
### Effect of Dissociation and Evaporation Rates  
Gas hydrate combustion includes a variety of interrelated processes: dissociation, ice melting, water evaporation, gas release, and oxidation reactions. Hydrate dissociation [45; 46; 47] and water evaporation from the particle surface [1; 48] are contributing factors to the  
Figure 4: The temperature fields of the gas hydrate ignition area under the conditions of conductive heating when varying the typical size of a gas hydrate particle at a substrate temperature of 973 K: (a) \(R_{\rm g}=0.25\) mm, (b) \(R_{\rm g}=0.5\) mm, (c) \(R_{\rm g}=1\) mm. ignition delay. Gas hydrate dissociation is a complicated process. The main characteristic of dissociation is its rate, which depends on numerous factors:  
\[W_{\rm d}=c_{\rm g}\rho_{\rm g}\cdot 2\cdot\pi\cdot R_{\rm d}, \tag{22}\]  
\[c_{\rm g}=\frac{2K_{\rm g}}{B_{\rm g}},\ K_{\rm g}=\frac{3k_{\rm R}(P_{\rm eq}-P _{\rm gas})}{b\cdot\rho_{\rm g}\cdot 2\cdot R_{\rm d}},\ k_{\rm R}=K_{\rm 0d}\cdot \exp\biggl{(}-\frac{E_{\rm a}}{RT_{\rm g}}\biggr{)},\ P_{\rm eq}=\exp\bigl{(}1 5.517-2105.16/T_{\rm g}\bigr{)}\cdot 1000,\]  
\[b=0.12\text{--methane concentration},\ B_{\rm g}=\frac{R_{\rm d}k_{\rm R}\mu_{ \rm g}}{k_{\rm F}\cdot\rho_{\rm g}},\ k_{\rm F}=\frac{P^{3}S_{\rm P}^{3}}{F \cdot(1-P)^{2}},\ S_{\rm p}=\pi R_{\rm P}^{2},\]  
where \(P\) is the porosity; \(F\) is the shape coefficient for sphere (150); \(R_{\rm P}\) is the pore radius (0.5 \(\mu\)m). The dissociation rate is affected by the pore density, the size of the gas hydrate particles, ambient temperature and pressure, the density of the heat flux supplied, and the type of the gas hydrate unit cell. The dissociation rate changes depending on the type of heat flux supplied to the gas hydrate particle, the heating source temperature, and heating conditions [48]. An increase in the heat flux density increases the dissociation rate of methane hydrate by almost one order of magnitude. At low heating temperatures, the density of the pore distribution in the gas hydrate decreases, which significantly changes the breakup rate during dissociation [49; 50]. A continuous increase in the heating source temperature leads to a steadily increasing dissociation rate of the hydrate inside the spherical particle, which enhances the combustion intensity of the flame [1]. Depending on the heating conditions and the type of gas hydrate, the dissociation rate changes in a wide range. In this research, the known mass dissociation rate \(w_{\rm d}\) was chosen in the range of 0.005-0.1 kg/m\({}^{2}\cdot\)s, which corresponded most closely to gas hydrate combustion. Figure 5a-c presents the ignition delay times determined for the gas hydrate when varying the mass dissociation rate and heating source temperature using radiant, convective, and conductive schemes. In every heating scheme, there was a decrease in the ignition delay times with the growth in the mass dissociation rate. Under the conditions of radiant heating, the gas hydrate ignition delay times decreased by 22-53% when the mass dissociation rate changed in the range of 0.005-0.1 kg/m\({}^{2}\cdot\)s and the heating source temperature increased from 973 K to 1273 K, respectively (Figure 5a). When supplying convective heat to the gas hydrate particle and varying the mass dissociation rate and temperature in the same way, the ignition delay times decreased by 11-89%, respectively (Figure 5b). During conductive heating, the ignition delay times decreased most dramatically by 79% to 89% when the mass dissociation rate increased from 0.005 kg/m\({}^{2}\cdot\)s to 0.1 kg/m\({}^{2}\cdot\)s (Figure 5c). It is clear in Figure 5a-c that at higher heating source temperatures, the mass dissociation rate changed the ignition delay times more significantly. The probability of autoignition of the gas hydrate increased with a rise in the dissociation rate and gas temperature. At 973 K, the ignition delay times changed little (by up to 20% during radiant and convective heating) (Figure 5a,b).