A full 3D Large Eddy Simulation (LES) of a four-stroke,
four-cylinder engine, performed with the AVBP-LES code, is
presented in this paper.
The drive for substantial CO₂ reductions in gasoline engines in
the light of the global energy crisis and environmental awareness
has increased research into gasoline engines and increased fuel
efficiencies. Precise prediction of aerodynamics, mixing,
combustion and pollutant formation are required so that CFD may
actively contribute to the improvement/optimization of combustion
chamber, intake/exhaust ducts and manifold shapes and volumes which
all contribute to the global performance and efficiency of an
engine.
One way to improve engine efficiency is to reduce the
cycle-to-cycle variability, through an improved understanding of
their sources and effects. The conventional RANS approach does not
allow addressing non-cyclic phenomena as it aims to compute the
average cycle. LES on the other hand is particularly well suited to
study unsteady flow effects and grants access to the description of
cyclic variations. When considering multi-cylinder engines,
cylinder-to-cylinder interactions are crucial issues. Consequently,
the whole engine has to be represented for a fully realistic
simulation.
The present study aims at illustrating the innovative usage of
LES to reproduce and understand unsteady flow interactions between
the cylinders of a four-cylinder gasoline engine. To achieve this
purpose, more than nine cycles of the full engine were computed.
The computational domain covers the whole geometry, including four
combustion chambers as well as the intake and exhaust ducts and
manifolds. Details on the methodology used - based on the AVBP LES
code - and on the results obtained are given. Cylinder-to-cylinder
and cycle-to-cycle discrepancies are shown and Fourier analysis is
used to understand the cylinder-to-cylinder influence.