In 2013, the European Federation for Transport and the Environment (T&E), a non-governmental organization whose objective is to raise awareness of Europe on environmental protection issues, commissioned a study to TUV Nord on the emissions of particulate matter produced from direct injection petrol engines.
In 3 years the Euro 6c regulation would come into force, which would have introduced a new limit on PM emissions of petrol engines based on the number of particles emitted: 600 billion particles per km. A big change considering that the Euro 5 limit value for diesel engines was 6,000 billion per km.
Given this, the Tuv Nord report, published on November 28, 2013 on the T&E website, brought to light data of fundamental importance:
- direct injection petrol engines emit particulate particles 10 times more than diesel engines equipped with DPF
- produce 1000 particles of particulate matter more than indirect injection petrol
The test, carried out on 3 direct injection petrol all compliant with the Euro 5 standard, showed that all cars also fell within the Euro 6b standard, but none in the Euro 6c standard, while the diesels were all already compliant.
The conclusion of Tuv Nord was clear: the use of the particulate filter solves the problem of high emissions from direct injection petrol engines and makes it possible to meet the requirements of the Euro 6 regulation.
Here GPF entered the scense.
(You can find TUV Nord report here: https://www.transportenvironment.org/sites/te/files/publications/TUV-Technical_report.pdf)
The GPF is the exhaust after-treatment device for direct injection petrol engines.
It consists of a monolith (filtering element) with a honeycomb structure, that is, formed by open and closed ducts alternately. This structure means that the gases must pass through certain porous channels, inside which the particulate matter is “captured”.
Upon reaching a certain temperature (about 600 °), the particulate thus accumulated is automatically eliminated through combustion (self-regeneration of the particulate filter).
The difference between GFP and DPF lies in the material with which the monolith is made and in the times of self-regeneration.
In the GPF the material used for the filtering system is cordierite (AIMg), while the DPF is made of silicon carbide (Sic).
This difference is due to the fact that cordierite better resists to high temperatures, which direct injection petrols reach much faster than diesels (this is also the reason why they pollute more, as also highlighted in the Transport & Environment study).
Furthermore, precisely because the direct injection petrol engines quickly reach the temperature necessary for self-regeneration to take place, the GPF lends itself well to driving in urban stretches, unlike the DPF which in these circumstances clogs up faster.
Attention to maintenance!
It has been said that for all these intrinsic characteristics, GFP, in theory, presents fewer problems from the point of view of maintenance.