Current and Future Trends of Gasoline Particulate Filter Technologies, Calibration Strategies and Aging Methods

Authors

Dipl.-Ing. Michael Görgen, Dr.-Ing. Martin Nijs, Dipl.-Ing. Helmut Lehn,
Dr.-Ing. Johannes Scharf, Dr.-Ing. Matthias Thewes, Dipl.-Ing. Mark Hendrikx,
FEV Europe GmbH, Aachen;
Johannes Claßen, MSc., Stefan Sterlepper, MSc.,
Institute for Combustion Engines, RWTH Aachen University, Aachen;
Dr.-Ing. Henning Baumgarten,
FEV Group GmbH, Aachen

Summary

To lower particulate matter (PM) and particulate number (PN) tailpipe emissions and to comply with European and Chinese Real Driving Emissions (RDE) legislation, application of particulate filters is the appropriate means for gasoline engine powered vehicles. This paper presents current and future trends of gasoline particulate filter (GPF) technologies, calibration strategies and ash loading determination methods.

There are four major determining factors that influence the particulate raw emission:

• Ethanol concentration and aromatic content in the fuel are of major impact, such as a 10 % ethanol concentration decreases and a 10 % of aromatic content increases the particle emission by up to 50 % for both MPI and DI engines.
• At cold start conditions, European and Chinese worst-case fuels can easily cause a GPF loading increase by 50% compared to certification fuel.
• PN numbers can easily increase by 20 %, when counting ultra-small particulates < 23 nm, which are difficult to measure with today’s standard particulate counters.
• In worst case RDE cycles with high engine loads, fast accelerations and unfortunate boundaries like high altitude or steep road gradients, PN raw emission can increase by factors.

These factors imply that a reliable adherence of the PM and PN emission standards almost invariably requires the application of a particulate filter.

The results of a representative study of the GPF-technology currently in introduction (> 25 GPF projects at FEV with > 15 OEMs) can be summarized as follows:

• The prime decision in regard to GPF hardware is currently determined by vehicle boundaries (main challenge for a first GPF installation in an existing vehicle is finding package volume for an adequate filter).
• Timely consideration of GPF application in a vehicle development program (hence, later SOP dates) lead to optimized GPF hardware.
• A trend towards a bigger share of uncoated GPFs is expected with increasing catalyst volumes (also driven by RDE).
• At catalyst to GPF volume ratios below 0.6, coated GPFs will stay the preferred choice to enhance the catalyst surface of the exhaust system to comply with RDE regulations.
• Often, more than one sensor for GPF control and monitoring is implemented, an evidence of the complexity of GPF calibration requirements (standard are a delta-pressure sensor plus one extra sensor e. g. a temperature sensor).

With the rising GPF share in gasoline powered vehicles, GPF aging for full-useful-life applications becomes more important. Aging of the catalytic layer of a coated GPF (or four-way-catalyst FWC) is state-of-the-art and is performed as with three-waycatalysts (TWC). However, “aging” in regard to ash loading is a GPF specific phenomenon. Ash originating from lubrication oil combustion accumulates in the GPF and increases the exhaust system´s back pressure over the life time of the vehicle.
Extensive long running vehicle tests > 100,000 km with run times of several thousand hours are required to investigate this subject. In parallel a quick ash loading procedure has been developed to accelerate GPF ash loading and aging significantly (up to 23 g of ash in 120 h have been realized).

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