Introduction

Development and implementation of an advanced combustion model for Diesel combustion for PSA Peugeot Citroën.

Objectives

The main objectives of this project were:

• Implementation of an advanced combustion model into a commercial CFD code
• Validation of the model against experimental data

Modeling approach

The basis of the combustion modeling approach is the GFSD (Generalized Flame Surface Density) model [1]. This modeling approach proved to be able to yield correct results for the prediction of the ignition delay and location, the transient flame development phase (the so-called premixed peak) and the quasi-stable flame structure.

Implementation of the model into a commercial CFD code

This work involved two phases:

• Calculation and coupling of laminar flame data to a commercial CFD code, in order to account for the transient ignition process
• Implementation of the turbulent combustion model into the CFD code via User Defined Functions

DI Diesel engine test case

The engine considered is a passenger car Diesel engine, using Direct Injection, Common Rail technology for the fuel injection.

Methodology of the 3D engine simulations

The in-cylinder domain considered was reduced using symmetry conditions, meaning that only a sector of the cylinder was meshed. The start of simulation is just after closure of the intake valve and the end of the simulation is close to the end of the expansion stroke. The boundary conditions were taken from experimental data.

Standard models were used for turbulence and spray physics. A custom model was used for the description of the fuel/air mixing process. The GFSD model accounted for species rate-of-change and heat release rate, using complex chemistry data from one-dimensional laminar diffusion flames.

Operating Conditions

The operating points considered have the following characteristics:

• 1640 rpm (part load case)
• Single injection
• 0 or 30% EGR (Exhaust Gas Recirculation)

Results

The results of the simulations were compared to experimental data for:

• Mean pressure curve
• Burnt fuel mass fraction

Also, detailed analysis was performed of ignition timing and location, as well as flame propagation and stabilisation. The image illustrates the quasi-steady, lifted Diesel spray flame.

References

1. F.A. Tap and D. Veynante, Proc. Combust. Inst. 30:919-926 (2005).