Optimizing operating conditions of swirl-assisted colorless distributed combustion of ammonia/hydrogen mixtures for enhanced thermal and emission performance

The effects of hydrogen enrichment and varying equivalence ratio on ammonia fuel were investigated under Colorless Distributed Combustion (CDC) conditions, aiming to optimize the operating parameters for the lowest NO x and unburned NH 3 emissions. In this context, changes in flame structures and temperature distributions, along with NO x and predicted unburned NH 3 emissions, were examined both experimentally and numerically under the CDC regime. In particular, the reduction in the equivalence ratio in fuel mixtures with low H 2 fractions prevented the achievement of lower O 2 concentrations for CDC conditions and narrowed the operational stability range. The CDC regime resulted in more uniform thermal fields under all conditions. Furthermore, lower H 2 fractions and leaner mixtures contributed to the homogenization of the thermal fields. Compared to conventional combustion conditions, NO x emissions for the 50 % NH 3 /50 % H 2 fuel mixture at a 17 % O 2 concentration were reduced by 82.2 %, 89.1 %, and 90.7 % at equivalence ratios of 0.9, 0.8, and 0.7, respectively. Under these conditions, predicted unburned NH 3 emissions were minimal at an equivalence ratio of 0.9, while they were observed to be 600 ± 95 ppm and 700 ± 110 ppm at 0.8 and 0.7, respectively. Reducing the H 2 fraction decreased NO x emissions while increasing NH 3 slip. This paper demonstrates the CDC regime as an effective strategy for mitigating NO x and NH 3 slip in the 50 % NH 3 /50 % H 2 mixture. Implementing these strategies will enable the optimized combustion of NH 3 , thus expanding its use as a zero-carbon fuel.