Investigation of ammonia cracking combined with lean-burn operation for zero-carbon combustion and NO/N2O/NO2 improvements

Abstract

Ammonia has received significant attention as a carbon-free fuel and a promising carrier of hydrogen. Ammonia cracking presents an effective method for on-line hydrogen production , eliminating the need for hydrogen transportation and storage. This paper aims to study the comprehensive impacts of ammonia cracking ratio (CR) and equivalence ratio (ER) on combustion performance and NO/N 2 O/NO 2 behaviors under lean-burn operation mode. The ammonia/hydrogen mechanism was updated and simplified to enhance the calculation efficiency in 3D simulation . Visualization measurements for flame propagation and NO and 3D simulations were simultaneously performed in a constant volume combustion chamber (CVCC). The results showed that ammonia blending with the cracked gas of H 2 /N 2 for CR can significantly enhance the combustion rate under lean-burn operation at an ER of 0.5. Nevertheless, this enhancement leads to an increase in NO x due to elevated OH and HNO formation, regardless of N 2 separation. In the context of varying ER, ranging from 0.5 to 0.3, the study revealed that increasing CR combined by decreasing ER at a certain point can sustain a higher combustion rate while reducing NO x emissions. For instance, CR45ER0.4 yields a much shorter combustion duration and lower NO x compared to pure ammonia at an ER of 1.0. However, a further increase in CR, such as CR80ER0.3, results in higher NO x emissions again. Moreover, complete cracking or separation from the non-cracked ammonia proves favorable for NO x elimination due to the absence of fuel-NO. The current study provides insights on high-efficiency and clean zero-carbon combustion technology.