The evolution of
hydrogen from methane decomposition in a liquid
metal bubble reactor (LMBR) has become a recent subject of interest;
this study examines a novel approach to hydrogen production from pyrolysis
of complex hydrocarbon fuels. Modeling hydrocarbon fuel decomposition
in an LMBR is executed in two stages of pyrolysis: First, primary
pyrolysis intermediates are simulated using a functional-group-based
kinetic model (FGMech). Then, a detailed high temperature mechanism
(AramcoMech 1.3 + KAUST PAH + 5 solid carbon chemistry) is applied
to simulate secondary pyrolysis of intermediates. The quantities of
major products of the secondary pyrolysis simulation (CH4, H2, Cs, C6H6) are approximated
by simplified regression equations. Further decomposition of smaller
hydrocarbons (until exiting the reactor) is simulated using a coupled
kinetic and hydrodynamics model that has been reported in the literature.
The mixing effects of bubble coalescence and breakup are investigated
in a comparative study on homogeneous and non-homogeneous reactors.
Finally, a qualitative relationship between H2 yield per
mass of fuel, functional group, and other factors such as temperature,
pressure, and residence time is analyzed. In general, the H/C ratio
and cyclic/aromatic content are the main features influencing total
conversion to H2.
Surrogate mixtures are routinely used for understanding gasoline fuel combustion in engine simulations. The general trend in surrogate formulation has been to increase the number of fuel components in a mixture to better emulate real fuel properties. Recently, a new surrogate design strategy based on functional group analysis of real gasolines was proposed using a minimal number of species [minimalist functional group (MFG)approach]. MFG surrogates (having just one or two components) could experimentally capture the ignition delay time (IDT), threshold sooting index, and smoke point of different gasoline fuels with hundreds of components. However, other combustion characteristics were not explored, and kinetic modeling of MFG surrogates was not reported. These aspects are addressed in this paper, where the combustion behavior of MFG surrogates for various gasolines was assessed by simulating IDT, jet-stirred reactor oxidation, and premixed laminar flame speeds using chemical kinetic modeling. MFG simulations were compared with experimental data of the real gasolines as well as with the more complex multicomponent (five to nine species) surrogates. This study reveals that binary MFG surrogate mixtures are capable of accurately simulating the combustion behavior of more complex gasoline fuels with hundreds of components.
The
pyrolysis of undiluted cyclohexane has been studied in a continuous
flow tubular reactor at temperatures from 913 to 1073 K and inlet
feed flow rates in the range 288–304 g·h–1 at 0.17 MPa reactor pressure with average reactor residence time
of 0.5 s calculated based on the pressure in the reactor, the temperature
profile along the reactor, and the molar flow rate along the reactor
estimated by the logarithmic average of the inlet and outlet molar
flows. The reactions lead to conversions between 2% and 95%. Forty-nine
products were identified and quantified using two-dimensional gas
chromatography equipped with thermal conductivity and flame ionization
detectors. The products with molecular weights between those of hydrogen
and naphthalene constitute more than 99 mass % of the total products.
A kinetic mechanism composed exclusively of elementary step reactions
with high pressure limit rate coefficients has been generated with
the automatic network generation tool “Genesys”. The
kinetic parameters for the reactions originate either directly from
high level ab initio calculations or from reported group additive
values which were derived from ab initio calculations. The Genesys
model performs well when compared to five models available in the
literature, and its predictions agree well with the experimental data
for 15 products without any adjustments of the kinetic parameters.
Reaction path analysis shows that cyclohexane consumption is initiated
by the unimolecular isomerization to 1-hexene but is overall dominated
by hydrogen abstraction reactions by hydrogen atoms and methyl radicals.
Dominant pathways to major products predicted with the new model are
discussed and compared to other well performing models in the literature.
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