Supercritical carbon dioxide (SC-CO₂) jet is a promising technology for the extraction of coalbed methane. As a key component in the process of jet formation, the nozzle is an essential factor affecting the efficiency with which an SC-CO₂ jet breaks coal and rock. The nozzle structure directly affects the energy conversion rate and flow field structure of the jet. Thus, the use of a suitable nozzle can maximize SC-CO₂ energy utilization, reducing energy loss and engineering costs while achieving energy conservation and emission reduction. Based on the conical convergent nozzle and the Laval nozzles, this study conducted an SC-CO₂ jet coal breakage experiment and an I-Scan pressure testing experiment using experimental research methods. The influence of nozzle structure on SC-CO₂ jet coal breakage was studied and the results indicate that when the inlet pressure is constant, the Laval nozzle has a higher energy conversion rate and a stronger coal breakage effect than the conical convergent nozzle. Furthermore, considering the combined effects of the energy conversion rates of Laval nozzles and energy dissipation under ambient pressure, a key parameter for assessing Laval nozzles was discovered: the expansion ratio. The results indicate that the impact of jet temperature on the expansion ratio is small and that increasing the erosion effect of an SC-CO₂ jet by increasing the jet temperature is an energy-consuming and inefficient method. Essentially, the optimum coal breakage effect of the SC-CO₂ jet is obtained when the expansion ratio of the Laval nozzle is between 1.07 and 1.29.

超临界二氧化碳（SC-CO ₂）射流是一种提取煤层气的有前途的技术。作为射流形成过程中的关键组件，喷嘴是影响SC-CO ₂射流破碎煤和岩石的效率的重要因素。喷嘴结构直接影响射流的能量转化率和流场结构。因此，使用合适的喷嘴可以最大化SC-CO _2的能量利用率，减少能量损失和工程成本，同时实现节能和减排。基于锥形会聚喷嘴和拉瓦尔喷嘴，本研究进行了SC-CO ₂喷气煤破碎实验和使用实验研究方法的I-Scan压力测试实验。研究了喷嘴结构对SC-CO ₂射流煤破损的影响，结果表明，在入口压力恒定的情况下，拉瓦尔喷嘴的能量转化率更高，破损效果也比锥形会聚喷嘴强。此外，考虑到拉瓦尔喷嘴的能量转换率和环境压力下的能量耗散的综合影响，发现了评估拉瓦尔喷嘴的关键参数：膨胀比。结果表明，射流温度对膨胀比的影响很小，并且增加了SC-CO ₂的腐蚀作用通过增加喷射温度来喷射是一种耗能且低效的方法。本质上，当拉瓦尔喷嘴的膨胀比在1.07至1.29之间时，可获得SC-CO ₂射流的最佳断煤效果。