This paper presents the simulation of in-cylinder stratified
mixture formation, spray motion, combustion and emissions in a
four-stroke and four valves direct injection spark ignition (DISI)
engine with a pent-roof combustion chamber by the computational
fluid dynamics (CFD) code. The Extended Coherent Flame Combustion
Model (ECFM), implemented in the AVL-Fire codes, was employed. The
key parameters of spray characteristics related to computing
settings, such as skew angle, cone angle and flow per pulse width
with experimental measurements were compared.
The numerical analysis is mainly focused on how the tumble flow
ratio and geometry of piston bowls affect the motion of
charge/spray in-cylinder, the formation of stratified mixture and
the combustion and emissions (NO and CO₂) for the wall-guided
stratified-charge spark-ignition DISI engine. But due to the fuel
injected during compression stroke, the effect of intake ports and
exhaust ports were not taken into consideration in this study. It
is found that the geometry of piston bowls has a major effect on
the mixture stratification in-cylinder, the combustion process and
others. In addition, the characteristics of the charge motion and
combustion, such as mean in-cylinder pressure, heat release rate
and accumulated heat release vary as a function of crank angle at
different injection timings and tumble flow ratios, based on one of
two combustion geometries. The results show that the injection
timing and piston bowl shape play very important roles for the
combustion process and mixture stratification. Furthermore, the
simulation provides an insight into the interaction of charge flow,
fuel spray, piston bowl as well as combustion.