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Development of a Reduced Mechanism for <i>n</i>-Heptane Fuel in HCCI Combustion Engines by Applying Combined Reduction Methods
Employing comprehensive chemical kinetics mechanisms
in predictive
models results in the high demand for simulation time, which makes
the use of these mechanisms questionable. Consequently, reduced mechanisms
of smaller sizes are needed. The objective of this study is to produce
reduced mechanisms of <i>n</i>-heptane fuel, by utilizing
a three-stage reduction process. This work is performed using a validated
single-zone homogeneous charge compression ignition (HCCI) combustion
model. To remove unimportant species at the first stage, the directed
relation graph with error propagation (DRGEP) is applied. In the second
stage, the computational singular perturbation (CSP) method is used
to eliminate insignificant reactions. In the third stage, because
of the change in the net production and consumption rate of species
as a result of utilizing the second stage and its effect on direct
interaction coefficients calculated with DRGEP method, once again
DRGEP is applied to the mechanism for further reduction. Peak pressure,
maximum heat release, and CA50 have been selected as representative
parameters for evaluating the performance of the reduced mechanism.
For the generated reduced mechanism at each reduction step, these
parameters are calculated and the deviations from the corresponding
value obtained by applying detailed mechanism to the model are evaluated
until user-specified error tolerances are exceeded. This combination
of methods successfully reduced the comprehensive Curran’s <i>n</i>-heptane mechanism (561 species and 2539 reactions) to
a reduced mechanism with only 118 species and 330 reactions, while
maintaining small errors (<2%), compared to the detailed mechanism.
The simulation time required for calculation by applying reduced mechanisms
is decreased from ∼601 min to 8 min, in comparison to the detailed
mechanism. In addition to matching pressure, temperature, and heat-release-rate
traces, the mass fraction of some important species calculated from
the reduced mechanism closely agree with the results obtained from
the detailed mechanism. The reduced mechanism is included as Supporting
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