In the near future, particulate number (PN) regulations, including the Euro 6 regulations, will be going into effective and becoming more stringent around the world targeted at gasoline engine vehicles.
There is a type of particulate filter that has used for diesel engine vehicles, as a means to satisfy PN regulations. There are two types of particulate filters. One is a “bare” or “adding-type” GPF that is uncoated with catalyst, and the other is a replaceable-type GPF that is coated with catalyst. The replaceable-type GPF (coated GPF) has advantages in terms of cost-performance, installation space, and lower level of pressure drop, compared to the uncoated GPF.
The three main functions required for a coated GPF are, an improvement of three-way catalytic performance, lowering of pressure drop, and PN filtration efficiency improvement. It means that they need such as the higher efficiency than a conventional three-way catalyst (TWC), lower level of pressure drop that won’t affect engine power output / fuel efficiency, and PN filtration efficiency enough to meet PN regulation. A high-level PN filtration efficiency is required to meet PN regulations.
The Zone-coating technology, which is utilized for TWCs, is also an effective means of improving the three-way catalytic performance of a coated GPF. The three-way catalytic performance of a coated GPF can be optimized by precious metal arrangement aiming at early warming up of the catalyst.
The GPF is used under higher temperatures than diesel engine and the amount of particulate matter (PM) is also less than in a diesel engine, so GPF coating in-the-wall is an effective way to reduce the pressure drop. Also, it was found that a deep coating into the wall helps maintain larger pore diameters and enlarges the flow route of the gas.
At the same time, coating on-the-wall also improved the PM filtration efficiency. This technology is utilized for diesel engine particulate filters (DPF) as well.
The combination of the above “Zone” / “in-the-wall” / “on-the-wall” coating, optimal design of GPF catalyst according to the OEM requirements (the three-way performance, the pressure drop, and the PN filtration) and the usage environment of each catalyst has become possible.