Hydrogen effect on flame extinction of hydrogen-enriched methane/air premixed flames: An assessment from the combustion safety point of view

Abstract

Hydrogen-enriched natural gas is a promising low-carbon fuel in combustion devices. To better assess its feasibility from the extinction prevention point of view, the extinction of near-limit premixed hydrogen-methane/air flames over a wide range of equivalence ratios was measured using the single-flame counterflow configuration. Results showed that the hydrogen addition resulted in a greater extinction stretch rate. Further analysis demonstrated that the extinction stretch rate of premixed hydrogen-methane/air flames linearly correlated with the corresponding reference flame speed. Thereby a combustion regime map diagram, separating the burning and extinction, was sketched. In addition, critical extinction Damkӧhlor number of premixed hydrogen-methane/air flames was investigated and it was found to be insensitive to the hydrogen addition and equivalence ratio. Finally, the hydrogen addition effect and the corresponding extinction response were assessed for two scenarios, 1) constant thermal load (gas turbine, gas-fired boilers, etc.), and 2) constant fuel injection pressure (gas stove, oven, etc.). The results indicated that H2 addition promoted the combustion safety by increasing the extinction stretch rates, but an allowable H2 variation window existed when considering the unexpected high-temperature damage of the burners. The allowable H2 variation window of Scenario 1 was found much broader than that of Scenario 2.