Comprehensive kinetic study on ammonia/ethylene counter-flow diffusion flames: influences of diluents

This study aimed to investigate the effects of ammonia addition on ethylene counter-flow diffusion flames with different diluents on the fuel or oxidizer side, using kinetic analyses. A special emphasis was put on assessing the coupled chemical effects of NH₃ and CO₂ on C₂H₄ combustion chemistry. The chemical effects could be evaluated by comparing fictitious inert NH₃ or CO₂ with normal active NH₃ or CO₂. The results revealed that the addition of NH₃ decreased the mole fractions and production rates of key soot precursors, such as acetylene, propynyl, and benzene. When CO₂ was used as the dilution gas, the coupled chemical effects of NH₃ and CO₂ were affected by the chemical effects of CO₂ to varying degrees. With the oxidizer-side CO₂ addition, the coupled chemical effects of NH₃ and CO₂ reduced the mole fractions of H, O, OH radicals, acetylene, propynyl, and benzene, while the effects differed from the fuel-side CO₂ addition. The coupled chemical effects of NH₃ and CO₂ also promoted the formation of aldehyde contaminants, such as acetaldehyde, to some extent, particularly with CO₂ addition on the oxidizer side.