In this work a numerical analysis of multiple-injection strategy
in homogeneous operation in DISI engines is presented.
Moving toward Euro 6 emission standards, one of the main
challenges for GDI engines is the reduction of particulate emission
in terms of mass and particle number. In fact, in stratified
operation, the droplets injected during compression stroke may
cause a significant amount of soot production, due to locally
non-premixed combustion. Besides, in medium and high load, the
liner and piston spray impingement is another possible reason of
production of soot emission. In order to meet the required
performance and emission targets, focusing on the reduction of
particulate emission, a multiple injection strategy can be
considered as an option to control both the mixture stratification
and the wall impingement.
In particular, in this work a multiple injection strategy during
intake stroke in homogeneous condition is analyzed. The analysis
makes use of advanced simulation tools, which allows to select
particular strategies to be validated on engine bench. First of
all, starting from a given injection strategy for a DISI engine,
some possible methods for splitting injection are considered and
their feasibility with a particular type of injector is validated
by means of a 1D model of the hydraulic and the complete engine
systems. Then the 1D models are integrated with 3D models of the
spray and the engine implemented into the Lib-ICE code, a set of
library and applications developed to simulate IC engines using the
OpenFOAM® technology. The engine cycle simulation is performed with
the new injection strategies. The advanced CFD computational tool
used for the investigation can manage piston and valve motion, fuel
injection, air/fuel mixing and wall film formation so that the
mixture formation process is effectively evaluated by means of the
simulation. The investigation performed allows to assess the basic
advantages of a multiple injection strategy: the reduction of the
wall film impingement and the better air/fuel ratio distribution at
the end of compression, which lead to lower soot formation.