Effects of ammonia addition on soot formation in hydrocarbon fuels combustion: Challenges and prospects

Ammonia has received great attention of researchers as a hydrogen-rich carbon-free fuel under the background of “carbon peak” and “carbon neutrality”. By discussing the surface growth and oxidation process of soot, this review deepens the understanding of the mechanism of the influence of ammonia addition on the surface growth and oxidation of soot in combustion reaction. The latest research results of soot formation in the combustion of ammonia/hydrocarbon mixtures are presented in this work, which analyzed the influence mechanism of ammonia on the formation of soot of hydrocarbon fuel, and reviewed the research status and development trend of ammonia mixed hydrocarbon fuel. The results showed that the decrease of soot volume fraction (SVF) and polycyclic aromatic hydrocarbons (PAHs) content can be measured with the increase of ammonia ratio in the blended fuel whether in laminar or turbulent flame, the inhibition effect of ammonia is due to the preemptive reaction between amino molecules and carbon-containing molecules in the combustion reaction tank, which generates carbon and nitrogen compounds, reducing the Hydrogen-Abstraction-C₂H₂(acetylene)-Addition (HACA) mechanism, thus gradually inhibiting the formation of large-size polycyclic aromatic hydrocarbons. In addition, the mixed combustion of ammonia and hydrocarbon fuel can also effectively reduce particulate emissions. Future researches will focus on exploring the interaction mechanism between nitrogen-containing compounds and high-carbon compounds in the flame. The reaction mechanism of ammonia on soot formation and complex ions in the flame under complex working conditions will be more accurately analyzed by advanced characterization methods.