Effects of gas content and ambient temperature on combustion characteristics of methane hydrate spheres

Abstract

Methane hydrate has the potential to become a high quality medium for gas storage and a special fuel because of its high efficiency for gas storage and its combustibility. It is important to study the factors that affect the combustion characteristics of methane hydrate. In this paper, the effects of gas content and ambient temperature on the combustion of methane hydrate spheres are investigated experimentally. The combustion flame of methane hydrate spheres with high gas content is bright yellow, whereas the combustion flame of methane hydrate spheres with low gas content is dim blue. With an increase in gas content, the methane hydrate sphere is easier to ignite and the combustion rate, residual gas content, flame height, flame oscillation frequency, and flame brightness all increase. However, the flame temperature at a height of 3 cm from the center of the sphere decreases. This is mainly because of the combustion of hydrate spheres with high gas content in a severe fuel excess state. The combustion characteristics of methane hydrate spheres in the ambient temperature range of 293 K–303 K are very similar. Also, the flame is bright yellow with insufficient combustion. With an increase in the ambient temperature, there are no differences in the residual gas content of methane hydrate spheres; the combustion rate, flame height, flame oscillation frequency, and flame brightness decrease slightly, and this is related to the self-preservation process. However, the flame temperature at a height of 6 cm from the center of the sphere increases. The increase in ambient temperature may have a similar effect with a decrease in gas content, and the root cause of this is that the slower release of methane is beneficial for mixing with the air in a better proportion. In addition, the combustion is more sufficient. The slower emission of combustion products also reduces the flow velocity, weakens the oscillation of the flame, and improves the stability of the flame.