Multi-energy well kinetic modeling of novel PAH formation pathways in flames
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Polycyclic Aromatic Hydrocarbons (PAHs) are harmful by-products formed during combustion of hydrocarbons under locally fuel-rich conditions followed by incomplete combustion. PAHs act as precursors during the formation of soot. PAHs and soot are harmful for human health and legislation limits the emission of unburned hydrocarbons and soot. Consequently, other measures are necessary in order to limit the production of PAHs and soot in internal combustion engines applications, entailing a possible decrease of fuel eﬃciency and higher technical requirements for automotive manufactures. The combustion chemistry of PAHs is not fully understood, which prompts the need of further investigations. The chemical dynamics shown by novel pathways of PAH formation involving vinylacetylene addition to the phenyl radical opens up new horizons for the potential contribution to PAH formation through this class of reactions. In the present work novel pathways of the formation of naphthalene and phenanthrene are investigated for a laminar premixed benzene ﬂame and a laminar ethylene diﬀusion ﬂame. The purpose is to improve the prediction of the aromatic species concentration in the ﬂames. A pathway chosen due the high potential aromatic yield is assessed through preliminary ﬂame calculations relying on simplifying assumptions concerning reaction rates. Certain isomerisation steps of the pathway occur within a time-scale characteristic of thermal relaxation processes. Therefore, the solution of the energy grained master equation is necessary in order to calculate the phenomenological reaction rates resulting from a non-equilibrium kinetic modeling. Quantum chemical calculations are performed in order to calculate molecular properties of the species involved. These properties are subsequently processed to determine the rate constants of the sequence of multi-energy well reactions. Moreover, the chemical dynamics of the pathway is analyzed and the eﬀect of temperature and pressure on the kinetic parameters is investigated. Despite of the potential yield demonstrated through the preliminary ﬂame calculations, the computed rate constants show that the studied reactions are insigniﬁcant for the formation of naphthalene and phenanthrene in the studied ﬂames. An eﬀort is put on evaluating if the non-equilibrium kinetic modeling adopted for the calculation of the kinetic parameters is consistent with the kinetic modeling used in the ﬂame calculations. The current work provides an eﬃcient method to compute rate constants of multi-energy well reactions at diﬀerent thermodynamic conditions, characteristic of ﬂames and of combustion in commercial devices or in internal combustion engines. Pathways with a slightly different chemical dynamics should be tested applying the current methodology. Moreover, further studies should be aimed at overcoming possible limits of the kinetic modeling of multi-energy well reactions occurring in combustion environments.
Place, publisher, year, edition, pages
2016. , 174 p.
Polycyclic Aromatic Hydrocarbons, soot, laminar ﬂame, ﬂame calculation, quantum chemical calculation, non-equilibrium kinetic modeling.
IdentifiersURN: urn:nbn:se:kth:diva-183558OAI: oai:DiVA.org:kth-183558DiVA: diva2:912559
Subject / course
Master of Science in Engineering - Industrial Engineering and Management
2016-02-09, HPT Library, Brinellvägen 68, Stockholm, 09:15 (English)
Jayasuriya, Jeevan, DoctorWaldheim, Björn, Doctor
Fransson, Torsten, Professor