Experimental and theoretical study of PAH and soot formation in laminar flames
Date: Wednesday, April 07, 2021, 04:00 PM - 05:00 PM
The emissions of soot and polycyclic aromatic hydrocarbons (PAHs) from the incomplete burning of hydrocarbon fuels pose great threats to the environment and human health. To reduce PAH and soot emissions, comprehensive understanding of their evolution process is essential. In this study, a series of researches is conducted to evaluate sooting tendency and to develop PAH mechanism experimentally and theoretically.
Sooting tendencies of oxygenated fuels are quantitively investigated in counterflow diffusion flames. Sooting limits are described by critical fuel and oxygen mole fractions measured with a laser scattering technique. The addition of dimethyl ether shows non-monotonic behavior on sooting tendency at elevated pressures, which is attributed to chemical effect based on kinetic simulations. Furthermore, the tendency of incipient soot formation of other oxygenated fuels (e.g., alcohol, acid, ether, ketone, and carbonate ester) is assessed using a similar approach. As the precursor of soot, PAH measurement using laser induced fluoresecnce is implemented to track the overall evolution processes from PAHs to incipient soot.
Developing PAH mechanism is essential in understanding foot formation. However, PAH formation and growth processes are not well understood. Based on previous researches, PAHs with 5-membered rings are abundant in flames. Therefore, the growth of PAHs with 5-membered ring is investigated concerning acenaphthylene (A2R5). The density functional theory (DFT) and transition state theory (TST) are adopted to calculate potential energy surfaces and reaction rate coefficients. The existence of 5-membered ring has appreciable impacts on PAH production, which facilitates the formation of planar PAHs with C2H substitution, thereby improving the existing PAH mechanism.
In PAH mechanisms, the thermochemistry properties are not all calculated but hypothesized to be equal to those of a similar structure. The simulation accuracy of the hypothesis is explored by discussing the sensitivity of the thermochemistry parameters in flame simulations. The group additivity method via THERM code is used to calculate the thermochemistry properties. PAH loading affects the sensitivity of thermochemistry properties to both flame temperature and product yields. The result shows that either accurate thermochemistry properties or reverse reaction rates should be provided in the mechanism to improve simulation accuracy.
Zepeng Li is a Ph.D. candidate supervised by Prof. William Roberts and Prof. Sukho Chung in Clean Combustion Research Center (CCRC). She joined ME program, PSE division as a Master student in August 2014, then started her Ph.D. study in 2016. Her research has been focusing on the PAH and soot formation in laminar flames using laser diagnostics and quantum chemistry methods.