Abstract: Natural gas (methane) hydrates have great potential as fuels. It is necessary to study the flame characteristics to evaluate its energy efficiency when directly burned as a fuel and the risk of storing and transporting natural gas as the form of hydrate. Here, the flame characteristics in the combustion of methane hydrate spheres under natural convective flow conditions were investigated. Physical parameters related to the flame, such as height, brightness, oscillation frequency, and temperature were used to characterize the combustion process. The results showed that the combustion process was divided into four stages according to the changes in flame characteristics. The flame height was mainly affected by the mass change rate and the diameter of methane hydrate sphere. Further, the combustion of methane hydrate spheres was unstable, as reflected in the oscillation of the flame height with a period of ∼0.1 s. A ‘dark region’ was found near the methane hydrate sphere surface, characterized by a dark flame and low temperatures. Increasing the initial center temperature had little effect on the flame characteristics, causing only a slight increase in flame height. The diameter of the hydrate spheres, on the other hand, had a significant effect on the combustion behavior. As the sphere diameter increased, the flame height increased dramatically, the oscillation frequency decreased, and the maximum flame temperature remained unchanged.

中文翻译：

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自然对流条件下甲烷水合物球体燃烧火焰特性的影响分析

摘要：天然气（甲烷）水合物作为燃料具有巨大的潜力。有必要研究火焰特性以评估其作为燃料直接燃烧时的能源效率以及以水合物形式储存和运输天然气的风险。在这里，研究了自然对流条件下甲烷水合物球体燃烧的火焰特性。与火焰相关的物理参数，如高度、亮度、振荡频率和温度，用于表征燃烧过程。结果表明，根据火焰特性的变化，将燃烧过程分为四个阶段。火焰高度主要受质量变化率和甲烷水合物球直径的影响。此外，甲烷水合物球体的燃烧是不稳定的，正如火焰高度的振荡所反映的那样，周期约为 0.1 秒。在甲烷水合物球体表面附近发现了一个“黑暗区域”，其特征是黑暗的火焰和低温。提高初始中心温度对火焰特性几乎没有影响，仅导致火焰高度略有增加。另一方面，水合物球体的直径对燃烧行为有显着影响。随着球体直径的增加，火焰高度急剧增加，振荡频率降低，最高火焰温度保持不变。提高初始中心温度对火焰特性几乎没有影响，仅导致火焰高度略有增加。另一方面，水合物球体的直径对燃烧行为有显着影响。随着球体直径的增加，火焰高度急剧增加，振荡频率降低，最高火焰温度保持不变。提高初始中心温度对火焰特性几乎没有影响，仅导致火焰高度略有增加。另一方面，水合物球体的直径对燃烧行为有显着影响。随着球体直径的增加，火焰高度急剧增加，振荡频率降低，最高火焰温度保持不变。