Modeling of EGR Mixing in an Engine Intake Manifold Using LES

A Sakowitz,S Reifarth,L Fuchs,M Mihaescu

doi:10.2516/ogst/2013118

Abstract

We investigate the mixing process of exhaust gases with fresh air in Internal Combustion Engines (ICE). For this purpose, the flow in an inlet manifold of a six-cylinder heavy-duty Diesel engine is computed using compressible Large Eddy Simulations (LES). The Exhaust Gas Recirculation (EGR) concentration is modeled as a passive scalar. The results are validated by on-engine measurements of the EGR concentration using COZ probes. The boundary conditions for the highly pulsating flow are taken partly from one-dimensional simulations, partly from pressure measurements on the engine. In order to assess the sensitivity to the boundary conditions, changes are applied to the base-line case. The mixing quality is evaluated in terms of cylinder-to-cylinder distribution and the spatial RMS over the outlet cross- sections. Different averaging techniques are applied. It was found that the temporal and spatial EGR distribution is different among the cylinders. The EGR distribution within the cylinder inlet is non-uniform. These factors imply that one should not use a time-averaged EGR value as indicator for the EGR content. Furthermore, it was found that the flow pulsations at the EGR inlet have a large influence on the EGR distribution. By comparing the LES results with measurements, it was shown that LES gives a better and deeper insight into the mixing in such turbulent, pulsating flow situations.

Highlights

Exhaust Gas Recirculation (EGR) is a technique commonly used in modern Internal Combustion Engines (ICE), in Diesel engines
The piping upstream of the plenum consists of two 90-degree bends and one 45-degree bend
Mass flow to that the flow is strongly pulsating, past the EGR inlet, which is situated at the second bend

Summary

Introduction

Exhaust Gas Recirculation (EGR) is a technique commonly used in modern Internal Combustion Engines (ICE), in Diesel engines. EGR reduces nitrogen oxide (NOx) emissions by lowering the oxygen concentration of the combustion gases and thereby the peak combustion temperature. This is possible because oxidation of nitrogen occurs only at high temperatures [1]. A non-uniform mixture (both among and inside the cylinders) can result in an increase of NOx and particulate emission as compared to a fully homogenous mixture. This has been shown by on-engine measurements performed for example by Maiboom et al [3] and Payri et al [2]

Methods

Results

Conclusion