Multi-dimensional models represent today consolidated tools to
simulate the combustion process in HCCI and diesel engines. Various
approaches are available for this purpose, it is however widely
accepted that detailed chemistry represents a fundamental
prerequisite to obtain satisfactory results when the engine runs
with complex injection strategies or advanced combustion modes.
Yet, integrating such mechanisms generally results in prohibitive
computational cost.
This paper presents a comprehensive methodology for fast and
efficient simulations of combustion in internal combustion engines
using detailed chemistry. For this purpose, techniques to tabulate
the species reaction rates and to reduce the chemical mechanisms on
the fly have been coupled. In this way, the computational overheads
related to the use of these mechanisms are significantly reduced
since tabulated reaction rates are re-used for cells with similar
compositions and, when it becomes necessary to perform direct
integration, only the relevant set of species and reactions is
taken into account.
The proposed approach named tabulation of dynamic adaptive
chemistry (TDAC) has been implemented in the Lib-ICE code, which is
a set of libraries and applications for IC engine modeling
developed using the OpenFOAM® technology. In particular, a modified
version of the in-situ adaptive tabulation (ISAT) algorithm has
been developed for systems with variable temperature and pressure,
and the directed relation graph (DRG) method has been used to
reduce the mechanism at run-time. The validation has been carried
out with HCCI and diesel cases both using a simplified case to
compare the results obtained with and without TDAC, and a detailed
case that is validated with experimental data. For each tested
condition, a detailed comparison between computed and experimental
data is provided along with the achieved speed-up factors compared
to the use of direct integration.