Objective The mixed combustion of hydrogen and natural gas offers a viable approach to facilitating the energy transition. When a substantial amount of fuel is injected into a confined space approaching the blowout limit, the accumulated mixture of fuel and air can easily reach the explosion limit, leading to an explosion in the event of a blowout. From this perspective, it is of great significance to accurately predict the blowout limit of hydrogen-doped natural gas for the safe application of hydrogen energy.
Methods This study aimed to investigate the blowout characteristics of hydrogen-doped natural gas using a specially designed experimental setup. The blowout limit of jet diffusion flames fueled by hydrogen-doped natural gas was explored, and the effects of hydrogen blending ratios and nozzle diameters on the blowout pressure and velocity were analyzed.
Results Compared with pure natural gas, hydrogen-doped natural gas demonstrated enhanced stability in jet diffusion flames, with flame turbulence occurring only at higher pressures within the pipeline. Moreover, larger nozzle diameters resulted in higher blowout velocities when the same fuel was burned, due to the increase in the Reynolds number and flame propagation velocity in the jet flow. This necessitated higher jet velocities to blow out the flame. Increasing hydrogen blending ratios had a more pronounced effect on raising the blowout velocity when larger nozzles were used. Specifically, the blowout velocity increased from 1.88 times to 2.81 times, as the hydrogen blending ratio increased from 10％ to 50％ and the nozzle diameter changed from 2 mm to 10 mm. Further exploration examined the applicability of extending the empirical correlation based on blowout velocities for hydrocarbon fuels to hydrogen-doped flames. Additionally, a predictive model for blowout velocity based on Damköhler numbers (Da) was proposed for hydrogen-doped natural gas.
Conclusion For the design of hydrogen-doped burners aimed at achieving higher blowout velocities, it is recommended to appropriately increase the nozzle diameters, which correspond to expanded safe combustion ranges. The research findings provide valuable insights into understanding the flame stability mechanisms of hydrogen-doped natural gas, which are significant for applications in the design of industrial burners.
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