Experimental study on the effect of impact target distance on coal breaking efficiency of high-pressure gas–liquid two-phase jet

The effective impact target distance is one of the key parameters determining whether high-pressure gas–liquid two-phase jet technology can be applied in underground coal breaking and permeability enhancement projects. To investigate the effect of target distance on the coal breaking efficiency of high-pressure gas–liquid two-phase jets, a high-pressure gas–liquid two-phase jet test system was established. Through a series of experiments, the distribution characteristics of the impact pressure of the high-pressure gas–liquid two-phase jet under different target distances were studied, and the erosion characteristics under various target distances were analyzed. The results show that the high-pressure gas–liquid two-phase jet exhibits a significant pulse effect under different target distances, and the pulse frequency is almost unaffected by the target distance. As the target distance increases, the fluctuation of the water jet impact pressure becomes more pronounced. The impact area of the high-pressure gas–liquid two-phase jet significantly increases with the target distance, and both the amplitude and frequency of the impact area changes increase with the target distance. As the target distance increases, both the depth and volume of the erosion holes created by the high-pressure gas–liquid two-phase jet continuously decrease, while the effective diameter of the erosion holes rapidly increases.