Development of a Phenomenological Soot Model Coupled with a Skeletal PAH Mechanism for Practical Engine Simulation

A new
chemical mechanism with 12 species and 26 reactions for formation
of polycyclic aromatic hydrocarbons (PAHs) was developed and integrated
into a skeletal mechanism for oxidation of primary reference fuel
(PRF). Coupled with the new skeletal PRF-PAH mechanism, an improved
phenomenological soot model was further constructed based on our previous
work. By validating against the experimental data on the related PAHs
in four premixed laminar flames of n-heptane/iso-octane
and three counterflow diffusion flames of n-heptane,
it is indicated that the major species concentrations were well reproduced
by the model. Moreover, validations of the new soot model show that
the soot yield, particle diameter, and number density were predicted
with reasonable agreement with the experimental data in a rich n-heptane shock tube over wide temperature and pressure
ranges. Compared with the soot model with acetylene as precursor species,
the new model agrees better with the measurement, which proves the
necessity of including PAHs chemistry for soot modeling. Finally,
the model was applied to simulate the soot distributions in n-heptane sprays in the Sandia constant-volume combustion
chamber under high EGR conditions, as well as the evolutions of PAH
and soot concentrations in an engine fueled with n-heptane. It is also found that the experimental data was reasonably
well reproduced by the model.