STYFF-DEXA - Simulation tool for dynamic flow analysis in foam filters
Overview
Background & policy context:
Market strategy of European cars manufacturers has led to a high-speed direct injection Diesel engines market share of around 40%, provided that the barrier of contemporary reductions of NOx and particulates follow Euro IV and beyond emissions legislation.
The STYFF project was the last on-going activity within the DEXA-cluster. The focus on the cluster has been to follow a systematic, concurrent and simultaneous engineering approach focusing on:
- The component technology integration aspect within ART-DEXA – Advanced Regeneration Technologies for Diesel exhaust after-treatment.
- The system design aspect within SYLOC-DEXA - System Level Optimisation and Control Tools for Diesel Exhaust After-treatment
- The quality assessment and particulate measurement aspect within PSICO-DEXA – Particulate Size and Composition measurements for Diesel exhaust after-treatment.
- The systematic specification of foam filter material and analysis of filter efficiency on a microscopic level within STYFF-DEXA – Simulation Tool for Dynamic Flow in Foam Filters.
Objectives:
The past projects ART-DEXA, PSICO-DEXA and SYLOC-DEXA have been focusing on so called “cake filtration” (wall-flow monoliths) technology for Diesel particulate removal.
The objective of STYFF-DEXA was to develop a simulation tool to study “deep-bed filtration” (cellular structures such as fibres or foams) materials.
Foams material can exhibit significant structural and functional advantages. Particulates in the exhaust are collected essentially on the struts surface along the whole thickness of the device, according to the "deep-filtration mechanism" whereas the gaseous fraction can flow through the open pores.
Methodology:
The project was carried out through the following steps:
- Development of a systematic specification and reconstruction method for foam materials. The foam structure can be specified/generated given some of its low-order statistical properties such as porosity and two-point pore-pore correlation functions.
- Validation of the generation/reconstruction method by comparing and analysing microscopic images of real foam structures and artificially generated foam patterns.
- Extension of an existing single-phase fluid mechanics solver which is based on the Lattice-Boltzmann (LB) method to enable the simulation of particle laden flows inside porous structures on single and multiple processor computer systems.
- Development and integration of sub-models concerning particulate deposition, soot burn-off (thermal, catalytic or NO2-assisted) and ash accumulation into the LB solver.
- Comparison and analysis of predicted permeabilities with measured ones available from the SYLOC-DEXA database and assessment of the regeneration efficiency of filter material by correlating predicted soot conversion rates (based on the true surface area) with experimental data available from the SYLOC-DEXA project.
- Analysis of pressure wave attenuation behaviour and its effect on noise reduction inside foam filters of different porosities using the parallelised version of the LB solver (to overcome single processor performance constraints).
- Development of an efficient and user-friendly simulation package consisting of an artificial foam generator, LB flow solver and results analyser which can be used as part of the SYLOC-DEXA toolkit or stand alone and which enables the investigation of innovative foam filter concepts such as for example the combination of filter materials of different porosity and surface coating or "synthetic foams" based on prescribed regular pore structures and pore size distributions.
- Generation of a results database containing all relevant geometric information, fluid flow and chemical kinetics parameters for foam filter materials to enable the extraction of integral (macroscopic) properties (such as porosity and permeability) which can be used by conventional Computational Fluid Dynamics (CFD) codes.
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