Methane deflagration promoted by enhancing ignition efficiency via hydrogen doping, with a view to fracturing shales

Abstract

The enhancement of shale gas explosion pressure is an unresolved issue in the emerging in-situ methane explosive fracturing. An effective approach to further enhance combustion and explosion characteristics is to promote ignition via improver doping. In this work, the enhancement of EIE (excess ignition energy) on the deflagration characteristics of CH4–CO–H2 mixtures was tested using a 20 L spherical setup, whereby the contribution of hydrogen, as an improver with higher thermal conductivity, to the enhanced effects was first explored. It is discovered that hydrogen doping contributes to thermal expansion and combustion, and the explosion pressure, rise rate and laminar burning velocity of methane at 0.6 equivalence ratio have been increased by 1.2%, 19.7% and 3.9% after loading 1 kJ EIE compared to loading minimum ignition energy, and can be further enhanced by 0.2%, 7.2% and 2.8% via hydrogen doping. Moreover, the promotion of hydrogen doping on ignition efficiency was demonstrated by quantitatively analyzing the underlying heat loss of EIE. Results indicate that even at 1.0 equivalence ratio, EIE would experience a significant heat loss of 54% in methane, whereas more energy would be used to promote combustion after hydrogen doping, ultimately achieving an ignition efficiency of up to 87%.