Reduced Chemistry for a Gasoline Surrogate Valid at Engine-Relevant Conditions

A detailed mechanism for the four-component
RD387 gasoline surrogate developed by Lawrence Livermore National
Laboratory has shown good agreement with experiments in engine-relevant
conditions. However, with 1388 species and 5933 reversible reactions,
this detailed mechanism is far too large to use in practical engine
simulations. Therefore, reduction of the detailed mechanism was performed
using a multi-stage approach consisting of the directed relation graph
with error propagation and sensitivity analysis (DRGEPSA) method,
unimportant reaction elimination, isomer lumping, and analytical quasi-steady-state
(QSS) reduction based on computational singular perturbation (CSP)
analysis. A new greedy sensitivity analysis algorithm was developed
and demonstrated to be capable of removing more species for the same
error limit compared to the conventional sensitivity analysis used
in directed relation graph (DRG)-based skeletal reduction methods.
Using this new greedy algorithm, several skeletal and reduced mechanisms
were developed at varying levels of complexity and for different target
condition ranges. The final skeletal and reduced mechanisms consisted
of 213 and 148 species, respectively, for a lean-to-stoichiometric,
low-temperature homogeneous charge compression ignition (HCCI)-like
range of conditions. For a lean-to-rich, high-temperature, spark ignition/compression
ignition (SI/CI)-like range of conditions, skeletal and reduced mechanisms
were developed with 97 and 79 species, respectively. The skeletal
and reduced mechanisms in this study were produced using an error
limit of 10% and validated using homogeneous autoignition simulations
over engine-relevant conditions; all showed good agreement in predicting
ignition delay. Furthermore, extended validation was performed, including
comparison of autoignition temperature profiles, perfectly stirred
reactor (PSR) temperature response curves and extinction turning points,
and laminar flame speed calculations. All of the extended validations
showed results within/near the 10% error limit, demonstrating the
adequacy of the resulting reduced chemistry.