Research Topic

Simulation of Turbulent Combustion Processes in GDI-engines using LES

Research topic

The call for environmental compatible and economical vehicles, still satisfaying demands for high performance, necessitates immense efforts to develop innovative engine concepts. Whereas direct injection gasoline(GDI) engines promise considerable fuel savings, they are prone to large variations in the flow and mixing field resulting from unsteady engine operations, like those due to cycle-to-cycle variations. These fluctuations may result in combustion failures leading to a total loss of the energy stored in a full cylinder load and to the ejection of unburnt hydrocarbons into environment. As Large Eddy Simulation (LES) technique allows to directly take into account flow unsteady effects it is well suited for this purpose. The objective is therefore to develop a 3D CFD LES engine simulation tool for the computation of In-cylinder combustion processes in realistic GDIengine configurations.

Recent work

First year research was based on the understanding of the code (kiva-3v), and implementation of a new LES model on it. After implementation and validation of the model, a simple engine was simulated in various cycle to compare old and new model. Fig.1 show one slide of engine cycle simulated to compare models.

After that the work proceed in combustion simulation direction. It was studied the original model in kiva and adapted on LES simulation with a new model implementation. This new model, called artificially thickened flame (ATF) is very simple but useful for LES simulation on IC engines, because it allow to use less cells in the grid than normal. In standard simulation the flame front could be 0.1-0.5 mm thick and to simulate properly it need minimum 3-5 cell on this area, this means 0.02-0.1mm of cell size, and bring to more millions cells for every simulation. Simulation with ATF model have flame thick 5-10 times (depends on the choose factor) bigger than before, this allow bigger cell and few computational time. Fig.2 show a simple combustion simulation in a isolated domain with moving piston on the bottom side of the cylinder.Turquoise surface represent the flame surface, contours of the slice are colored with mass fuel quantity.

Fig.1
Fig.2

Key research area

Multi-Physics; Combustion modeling and simulation

The engine group of energy and power plant department focused on LES simulation of a complete engine cycle for internal combustion engines (ICE).
Principal issues of this research area are:

  1. Study LES modeling to study cycle-to-cycle variation inside ICE to predict some particular phenomena like misfiring and pollutants formation;
  2. Bring LES as simple as possible to demonstrate that will be used in industry environment

Contact

Matteo Ghelfi
Dipl.-Ing.

Address:

Dolivostraße 15

D-64293 Darmstadt

Germany

Phone:

+49 6151 16 - 24401 or 24402

Fax:

+49 6151 16 - 24404

Office:

S4|10-308

Email:

ghelfi (at) gsc.tu...

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