Haralampous O. and Koltsakis G., “3D Simulation Models for After-Treatment Systems” in Onorati A. and Montenegro G. (ed) “1D and MultiD Modeling Techniques for IC Engine Simulation”, 2nd edition, SAE International, ISBN 978-1-4686-0993-6, 2026

Haralampous O. and Koltsakis G., “3D Simulation Models for After-Treatment Systems” in Onorati A. and Montenegro G. (ed) “1D and Multi-D Modeling Techniques for IC Engine Simulation”, SAE International, ISBN 9780768093520, 2020

The inlet geometry of an exhaust system is of critical importance for its performance during cold start . Asymmetrical inlet pipes and cones are often used upstream of close-coupled catalytic converters. As a result, flow and temperature non-uniformities arise during transient conditions, such as the cold start of the engine. A fast and and complete heat-up of the catalytic converter is critical during this period to facilitate activation of chemical reactions and emission control. Within this project a series of inlet geometries where simulated under transient conditions to assess the effects of asymmetric features. The simulations were performed with exothermia suite, which integrates Crossfire, a library for 3d mesh generation and OpenFOAM interface developed by the University of Thessaly.

This project followed the earlier development of crossfire, a library that couples the commercial software exothermia suite and OpenFOAM for the simulation of exhaust systems with components of standard geometry. Real-life diffusers and inlet manifold deviate substantially from standard 3d geometries due to the restrictions in the engine bay and underneath the vehicle, as shown in the pictures. The 3d geometry introduces non-uniformities that need to be accurately modeled in order to predict the performance of the complete exhaust system. With the updated library all free-form components can be imported and simulated in exothermia suite, covering fully the needs of R&D for exhaust systems. All major 3d mesh file formats are supported, hence the use of third party CFD tools is unnecessary.

• Assoc. Prof. Onoufrios Haralampous – Principal investigator
• Dr Chris Dritselis – Senior researcher
• Dr Marios Mastrokalos – New researcher
• Dr Fotini Tzorbatzoglou – New researcher

The project dealt with with the performance of partially Failed Particulate Filters, often found in older vehicles due to inadequate maintenance or tampering of the exhaust system. Experimental and computational methods were applied at the smallest relevant scale to clarify the necessary flow and filtration phenomena and furthermore to quantify the effects in terms of diminished filtration efficiency. Interestingly additional filtration phenomena were identified in the intact and damaged DPFs, besides the prevailing deep-bed and surface filtration mechanism due to wall flow, while it was shown that prediction of pressure drop and filtration efficiency in an intact/damaged DPF under real-driving conditions is possible despite the difficulties.

The project involved the development of crossfire, a software library, which facilitates the coupling of OpenFOAM with other CAE tools. In this case OpenFOAM was coupled with exothermia suite (formerly axisuite) in order to model for exhaust aftertreatment systems. Specifically the following functionalities were implemented:

• Preprocessing
  • 3d mesh generation of exhaust system using simple geometrical parameters for standard components (cylindrical substrates, axisymmetric cones, curved or straight cylindrical pipes)
  • Definition of physicochemical model and numerical method parameters in OpenFOAM files
• Transient simulation with a customized OpenFOAM solver taking into account
  • momentum balance using an equivalent porous medium for the substrates (flow-through or wall-flow)
  • energy balance with pipe heat losses and source terms for the convection and chemical reactions in the substrates
  • mass balances of gaseous and solid species (soot and ash) with source terms for chemical reactions, absorption and filtration in the monoliths
• Post-processing
  • Reading and analysis of OpenFOAM results

The project was funded by Exothermia SA. The development of the library and the management of the project was undertaken by Onoufrios Haralampous with the assistance of Dimitrios Mastellos. On behalf of Exothermia SA, Dr Theodoros Atmakidis was responsible for the collaboration and integration in exothermia suite.