The role of C3 and C4 species in forming naphthalene in counterflow diffusion flames

Allene and 1-buten-3-yne ( ) represent important intermediates in forming polycyclic aromatic hydrocarbons and soot. Hydrogen abstraction from allene provides the resonance-stabilized propargyl radical fueling molecular growth kinetics. However, the kinetics associated with 1-buten-3-yne and its involvement in the formation and growth of aromatics still need to be fully understood. One of the challenges is the complexity of the relevant chemistry in most combustion environments, which includes fuel-specific reactions in addition to reactions of species. This work attempts to simplify the relevant chemistry by using 1-buten-3-yne as fuel for the first time in counterflow diffusion flames. A pure allene and a 75/25 mol % allene/1-buten-3-yne blend flame were examined using gas chromatography-mass spectrometry and time-of-flight mass spectrometry. The boundary and operating conditions feature close equilibrium temperature, stoichiometric mixture fraction, and strain rate, allowing a meaningful kinetic comparison between the flames. Speciation data from both instruments were consistent for the vast majority of the species. The experimental results were compared to simulations performed with an updated, extensively validated, detailed chemical kinetic model. Notably, adding 1-buten-3-yne to the fuel reduced benzene and increased the formation of naphthalene. This showcases that the availability of and species impacts the kinetics of the two species differently. Pathway analyses revealed that benzene formation highly depends on species, while naphthalene relies on and species. Naphthalene formation depends on the abundance of 1,3-butadiyne ( ) and proceeds mainly via the and pathways. Other pathways, such as HACA and phenyl radical-addition to , exhibited a minor impact. The present work highlights that uncertainties in the -related chemistry are highly relevant for the modeling of aromatics and may affect naphthalene predictions. Therefore, the experimental data of this study will provide a unique validation target for future kinetic model development.