Study on the rock-breaking characteristics of high-energy pulsed plasma jet for granite

Plasma jet rock-breaking technology, characterized by its high rock-breaking efficiency, low specific energy, and absence of mechanical wear, is one of the most promising methods for efficiently fracturing hard rock formations such as hot dry rock (HDR). This study designed a novel high-energy pulsed plasma power supply and pulsed gas supply system to achieve rock fracturing through the instantaneous high-temperature and thermal stress impact of the high-energy pulsed plasma jet on the rock surface. This paper conducted comparative experiments with a traditional constant plasma jet. The impact of crucial electrical parameters (peak current, valley current, frequency, and duty cycle) and rock initial temperature on the damage and fracturing patterns of granite was extensively investigated. Comprehensive evaluation criteria, including removal mass, diameter, depth, rate of penetration, and specific energy, were employed to study the effects meticulously. The results indicate that the pulsed plasma jet significantly enhances energy utilization, effectively reducing the occurrence of thermal melting. The specific energy decreased significantly by 54.74%, while the rate of penetration increased by 17.81%. Additionally, electrode wear was reduced by 50.06%, extending the lifespan of the plasma bit. Parametric analysis revealed that the peak current is the primary factor influencing the rock-breaking performance and efficiency. The valley current has minimal impact on hole morphology but significantly affects specific energy. Frequency and duty cycle can be adjusted to optimize the single-pulse energy, achieving the best specific energy and efficiency. Additionally, the rock temperature has a great influence on the breaking effect. The fracturing characteristics of granite were also analyzed from a microscopic level. Based on the experimental results, recommended parameters of pulsed plasma jet are provided for breaking granite. These findings offer guidance for high-energy pulsed plasma jet drilling of HDR.