Effects of the diameter and the initial center temperature on the combustion characteristics of methane hydrate spheres

The safe storage and transportation of methane hydrate, the in situ combustion of hydrates for deep mining, and the design of high-efficiency burners that directly use methane hydrate as fuel all require research on methane hydrate combustion characteristics. In this paper, the combustion characteristics of methane hydrate spheres in a natural convective flow were investigated, and the effects of the hydrate sphere diameter and the initial center temperature on their combustion characteristics were analyzed. The results demonstrated that the sphere diameter substantially affected the combustion process. At a lower initial center temperature (<−80 °C), methane hydrate spheres with diameters of 2 cm and 2.7 cm completely burned. In contrast, due to self-preservation in the 1.2-cm diameter methane hydrate sphere, the continuous water film on the surface was cooled by the inner low-temperature hydrate. This resulted in the formation of a continuous ice layer, which inhibited further dissociation of the internal hydrate, and the flame was rapidly extinguished. As the initial center temperature increased, the combustion time gradually decreased, and complete combustion of the 1.2-cm methane hydrate sphere was realized. During the combustion of the hydrate spheres, the variation in the diameter obeyed the D2 law, and the combustion rate decreased when the diameter increased or when the initial center temperature decreased.