Numerical Study on Multiple Injection Strategies in DISI Engines for Particulate Emission Control 2012-01-0400

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.