Electric ignition of sandstone fracturing in methane/air premixed gas in coal mines: Novel insights from ignition sources in a goaf

Abstract

Gas explosions in coal mine goafs are associated with the roof rock fracturing. An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing. The electrical responses, luminescent emissions, and ignition characteristics during tensile and compressive failure of sandstones were analyzed in methane/air premixed gas environments. Results indicate that the application of mechanical loading induces the emergence of electrical signals on rock surfaces and in the surrounding atmosphere. This phenomenon is attributed to the generation, accumulation, and subsequent release of free charges during the deformation and fracture within the sandstone. Compressive failure proved to be more conducive to free charge generation than tensile failure, owing to more crack connections. Furthermore, a precipitous increase in surface and external voltages was observed during complete fracturing, a consequence of electron emission from crack tips within the rock structure. Moreover, the ionization induces luminous emissions owing to the collision of energetic electrons released from gas molecules in methane/air mixtures. A strong positive correlation (R²=0.9429) was identified between luminescence intensity and the magnitude of electrical discharge resulting from rock fracture. Notably, such discharge by rock fracturing can be capable of igniting the premixed gas, particularly when the quartz content exceeds 61%. Piezoelectric effects and crack propagation are crucial mechanisms in the causal chain of the charge generation, discharge, and ionization triggered by rock fractures. Based on the above laboratory results, electric ignition of the transient roof fracturing caused by stress mutations can serve as a new potential ignition source for gas explosions in the goaf. These results offer new insights into the prevention and control of gas explosions.

Keywords

Gas explosions / Roof sandstone / Electric ignition / Luminous emission / Piezoelectric effect / Crack propagation

Acknowledgements

This work was supported by the National Natural Science Foun-dation of China (Nos. 52130411, 52174219 and 52174220), the Natural Science Foundation of Jiangsu Province (No. BK20240104), and the Fundamental Research Funds for the Central Universities (No. 2024-11044).

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