## 3 Results and Discussion
### Effect of Hydrate Particle Size
Under the conditions of radiant heating (Figure 3a), a four-fold increase in the hydrate particle radius increased the ignition delay times by 35% on average at a heating source temperature of 973-1273 K. When a gas hydrate was conductively heated (Figure 3b) at relatively low heating source temperatures (973 K), a change in the particle radius from 0.25 mm to 1 mm increased the ignition delay times by 77% (from 0.01145 s to 0.049 s). At high heating source temperatures (over 1173 K), the ignition delay times grew by 20% with an increase in the radius when conductive heating was used (Figure 3b). Thus, during conductive heating under high-temperature conditions, the gas hydrate ignites approximately with the same delay irrespective of its radius. Under the conditions of convective heating, the opposite is the case: at \(T=973\) K, the ignition delay times increase by 68% when the radius \(R_{\text{g}}\) changes in the range of 0.25-1 mm. At a heating source temperature of 1273 K, \(\tau\) decreases by 90% (Figure 3c). Such a difference from the conductive heating scheme has the following explanation. When there is convection, the heating of a particle from the external gas is determined by the Nusselt number (Nu), which is proportional to the square root of the Reynolds number (Re) in the laminar gas flow (i.e., the convective heat transfer coefficient for the gas phase \(\alpha\)\(\sim\)1/(\(R_{0}\))\({}^{0.5}\)), where \(R_{0}\) is the particle radius. With a decrease in the radius, the heat flux from the gas to the particle increases, as does the heating and dissociation rates. Thus, the heat flux for a particle with \(R_{0}=0.25\) mm will be twice as high (\(R_{0}\) decreases four times) when compared to a particle with \(R_{0}=1\) mm. As above-mentioned, the growth of the dissociation rate leads to lower ignition delay times. Thus, when there is convection, two factors contribute to a significantly lower ignition delay time. The heat exchange coefficient is inversely proportional to the radius (1/\(R_{0}\)) and is related to convection in the form (\(\sim\)1/(\(R_{0}\))\({}^{0.5}\)). The total effect gives \(\sim\)1/(\(R_{0}\))\({}^{1.5}\). This is accounted for by the fact that under the conditions of convective heating at high temperatures, the gas hydrate pores open faster for gas release. The larger the gas hydrate particle radius, the more pores are formed on the hydrate surface. In turn, the heat flux supplied from below to the gas hydrate with a larger radius blows off the water layer resulting from the melting of ice to the open pores, thus preventing the gas release, which leads to higher ignition delay times. The growth of the particle diameter increases the thickness of the water film. This decreases the gas flow (growth of the gas resistance through the water film) and increases the water flow to the combustion zone, which reduces the reaction rate in the flame region. The hydrate sample with \(R_{\text{g}}\) = 0.25 mm was characterized by a low content of gas, which led to a low combustion rate and lower heat transfer to the hydrate particle (Figure 4a-c). Figure 4a clearly shows great temperature fluctuations in closer proximity to the hydrate sample than they were in Figure 4b,c, where the gas hydrate particles of larger typical sizes are presented. Figure 3: The gas hydrate ignition delay times when varying the gas hydrate particle radius and heating medium temperature for three heat exchange schemes: (**a**) radiant, (**b**) conductive, (**c**) convective.