Modeling the Role of Hydrogen Strategies in Mitigating Unburned Ammonia and Carbonyl Pollutants from Ammonia/Methanol Combustion

This study numerically investigated the effectiveness of direct hydrogen addition versus ammonia cracking in reducing unburned ammonia and carbonyl pollutant emissions during ammonia/methanol combustion. Simulation using a modified Chemkin II/Premic code examined equivalence ratios from 0.7 to 1.2 and hydrogen incorporation levels up to 60%. Direct hydrogen addition increased unburned NH3 emissions by 196% under lean conditions (Φ = 0.7) but only 42% under rich conditions (Φ = 1.2), while ammonia cracking reduced NH3 emissions by up to 17 000-fold. Formaldehyde decreased by 45.9% (Φ = 1) with hydrogen addition, outperforming ammonia cracking (28% reduction), due to H-radical-driven consumption. Acetaldehyde emissions follow a U-shaped trend increasing under lean conditions, but decreasing in fuel-rich environments, with direct hydrogen addition achieving a 19% reduction at Φ = 1.2. These findings highlight a trade-off between hydrogen strategies, with ammonia cracking better suited for minimizing unburned ammonia and direct hydrogen addition more effective at reducing carbonyl compounds. Optimizing hydrogen enrichment in ammonia/methanol combustion is crucial for balancing emission control and combustion efficiency in future sustainable fuel applications.