Flame dynamics and emissions in stratified ammonia/hydrogen/nitrogen-air flames

Ammonia is a promising hydrogen carrying fuel that, when partially cracked into mixtures of ammonia/hydrogen/nitrogen, can have similar combustion properties as methane. However, emissions of nitrogen oxides and nitrous oxide remain a significant challenge, and reduction of these emissions is paramount for partially cracked ammonia to be feasible zero-carbon fuel. A rich-quench-lean staged combustion approach is a promising strategy for achieving this but it comes with practical challenges such as ammonia slip and the need for new stationary gas turbine infrastructure. While single-stage lean concepts have been inhibited by high levels of emissions, new strategies that reduce emissions would be critical. This work explores stratification as a mechanism to reduce NOx emissions by conducting detailed 2D simulations of stratified partially cracked ammonia-air flames. For a fixed overall equivalence ratio and cracking percentage, the relative ammonia to hydrogen content is varied locally in space. The magnitude and length scale of the stratification are varied to understand their independent impacts. By comparing the results against a dataset for an identical simulation setup with homogenous reactants, the effect of fuel mixture stratification on emissions formation is assessed.