Ammonia usage instead of hydrogen in Methane-Hydrogen Blended fuel mixture under highly preheated and dilution Condition: Chemical Perspective

Abstract

This study investigates the replacement of hydrogen with ammonia in a burner simulating the Moderate or Intense Low-Oxygen Dilution (MILD) combustion regime for methane/hydrogen. Ammonia is a hydrogen carrier with fewer concerns regarding safety, cost, and transportation than hydrogen; however, it has some other drawbacks regarding reactivity and pollutant formation. The effects on flame structure and NOx formation are examined using three detailed chemical mechanisms: GRI, Okafor, and Sandiego, to isolate the influence of chemical mechanisms in the analysis. A RANS approach with the Eddy Dissipation Combustion (EDC) model, along with zero-dimensional well-stirred reactor models, focuses specifically on the MILD region. Ammonia replaces hydrogen in a methane/hydrogen mixture, with a maximum substitution of 50%. The results indicate that ammonia enhances methane ignition routes and its conversion to CO compared to hydrogen within the studied range. Additionally, contradictory combustion efficiency behaviors related to ammonia slip and NOx formation can be mitigated through high dilution for NOx control and high preheating for ammonia control. The addition of ammonia leads to an expansion of the heat release area while simultaneously boosting both NOx and DeNOx chemical pathway.