Sectional soot model coupled to tabulated chemistry for Diesel RANS simulations
Résumé
In future Euro norms, the soot volume fraction and the soot number density will be regulated. Car manufacturers
need therefore accurate soot models for piston engine emissions prediction in order to develop
future engine concepts. This paper addresses this question by coupling a sectional soot model with a tabulated
combustion model for RANS simulations of Diesel engines. The sectional soot model, based on the
work of Netzell et al. (2007), is implemented in the IFP-C3D RANS CFD code. At each time and location,
transport equations are solved for several soot sections, including source terms for collisional and chemical
processes. The soot model is coupled to a tabulated combustion model derived from the Engine
Approximated Diffusion Flame one (EADF) (Michel and Colin, 2013). It allows to represent the minor species
required by the soot model with a much lower computational cost than a kinetic solver. In order to
evaluate the soot model coupled to the resulting combustion model called Variable Pressure
Homogeneous Tabulated Chemistry (VPTHC), it is compared to the same soot model directly coupled
to a complex chemistry solver. As this comparison can hardly be performed on a real Diesel engine case
due to the very high CPU time involved by the chemical solver, it is performed on a variable volume and
fuel/air ratio case which retains the essential features of a Diesel engine. Results show that the proposed
coupling recovers with reasonable accuracy the evolution of the soot volume fraction and distribution.
Finally, an experimental database of Diesel operating points is simulated. The database includes points
with a commercial Diesel fuel and the computed surrogate (30% 1-Methylnaphthalene and 70% Decane
in liquid volume) to validate the models against the experiments. Soot yields predictions from the model
show an improvement against the current standards and reach industrial target of accuracy for most of
the database while the model also provides a good estimation of the soot particles distributions in size.