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Innovative particle trap system for future diesel engines

Final Report Summary - IPSY (Innovative particle trap system for future diesel engines)

In order to solve today's drawbacks in diesel particulate filter (DPF) application and to meet future boundary conditions the EU funded project IPSY was started. In the focus of this project was the research and development of an alternative DPF approach. Today the DPF has become state-of-the-art in passenger vehicles. This allows undershooting the current EU4 particulate matter (PM) limits by far, typically reaching EU5 level. In order to meet the future regulations (EU5 and EU6) a DPF will remain mandatory.

Main motivation was the reduction of soot combustion temperature by the utilisation of higher soot reactivity with HCCI combustion and also by a new filter design with internal heat recovery capability and an advanced multifunctional catalyst that enhances the catalytic soot conversion. In detail, the project was setup with the following steps:
- feneration of a database for HCCI exhaust emissions and soot morphology (Istituto Motori, Italy; IFP, France);
- development of a new particulate trap system with enhanced catalytic effect (Aerosol and particle technology laboratory, Greece);
- setup of a detailed model for the new particulate trap with focus on the soot-catalyst contact and the influence of the soot morphology (Universidad Politecnica de Valencia, Spain; FEV Motorentechnik GmbH, Germany; Cracow University of Technology, Poland);
- development of an advanced operation and control strategy for the new system (Institute of combustion engines, University of Technology Aachen, Germany Universidad Politecnica de Valencia, Spain; FEV Motorentechnik GmbH, Germany);
- testing and investigation of the potential of the system (Fundaçion Cidaut, Spain; Universidad Politecnica de Valencia, Spain; IFP, France).

Analysis of the exhaust gas and detailed investigation of the soot morphology and reactivity were performed and pointed out the influence of future combustion systems on DPF application, mainly by the following factors:
- same or slightly elevated exhaust temperature profiles;
- significantly lowered NOx emissions and slightly lowered PM emissions, that reduce the NO2-regeneration effect in the filter;
- higher CO and HC raw emissions effecting the thermal management of the filter;
- different soot composition with increased share of volatile and soluble organic fractions is presenting significantly higher soot reactivity.
No specific morphology difference from macroscopic aspect. Mu-Raman spectroscopy analysis is ongoing to further research the correlation of soot structure and reactivity.

The advanced features of the IPSY filter system were based on a higher soot-to-catalyst contact, which required deep-bed filtration in the catalyst layer, an increased soot reactivity resulting from a HCCI combustion system as well as an advanced operation strategy. A 3D-computational fluids dynamics (CFD) model of the IPSY filter has been setup with main focus on the prediction of deep-bed filtration mechanisms and influence of soot morphology on the reactivity. The model displays each filter channel by several computational cells to achieve very high accuracy. It contains a fluid and a solid part, which are connected by enthalpy source terms. Sub-routines for the filtration behaviour are derived from a 1D detailed physical pore model, which is directly parameterised by the physical properties of soot and filter substrate. The CFD model covered all physical effects, which are relevant for soot load and combustion. The calculation of the system performance and the development of a new operation strategy require a model that also covers the interaction between exhaust system and engine. Therefore, a 1D model was setup and extended. A new calculation methodology, which is based on the independent time discretisation of the ducts, has been developed at the beginning of this task. Subsequently, models for both HCCI and conventional diesel engine have been defined, and the optimum configuration of the exhaust line stressing emphasis on the influence of DPF position on engine performance has been determined.

Based on the first year results from the analysis of the internal heat recovery concepts and the developments on the multifunctional catalyst synthesis and application, a full-scale MFR prototype was built. During the first six months of the second year this prototype was evaluated against the project emission targets. The MFR internal heat recovery capability was verified via tests on a flow test bench and on the real engine exhaust under fast regeneration conditions.

During the second semester of the second year two MFR prototypes were manufactured. The prototypes were equipped with pressure and temperatures sensors for monitoring the filter operation during the testing on the real engine exhaust. A dedicated system was built for the data acquisition and storage during the MFR operation. The prototypes have been tested in the conventional diesel exhaust of the APTL and their performance has been evaluated.

In the third period the MFR was tested in both, conventional as well as HCCI operation. The filter was aged at CIDAUT and the performance was measured on a conventional engine prior and after the aging. In parallel the performance in HCCI operation was tested at IFP.

The filtration efficiency of the filter was excellent and was retained after aging. The catalytic activity of the filter was significantly higher than the SA filters and was also retained after aging. The filter backpressure was comparable (or even better) than the SA filters. The effect of aging on the filter backpressure is either insignificant (UPVLC) or it causes a slight increase (APTL) mainly due to the accumulated ash particles originating from the engine oil consumption.

The IPSY MFR showed huge potential to reduce the fuel penalty of today's DPF regeneration operation. Cycle simulations have shown the possibility of fuel penalty reduction by approximately 25 % under real driving conditions. During the NEDC with a standard regeneration strategy over 45 % of the fuel penalty could be saved. The IPSY coated filter is also able to regenerate during low load phases without HC conversion in the DOC. This is a big advantage in terms of avoiding oil dilution, as late post injection is not longer needed in many engine operating points. The new IPSY filter combined with an optimized operation strategy that are realised by adequate ECU functions form a complete and new diesel particulate filter concept. This will contribute to the future compliance with the particulate matter and number emission legislation and at the same time address today's open development challenges.

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