What is a petrol particulate filter and how does it work?
Diesel cars have been fitted with particulate filters for years, and now petrol cars are getting them as well in order to reduce pollution...
A growing number of petrol cars are being fitted with petrol particulate filters – also called gasoline particulate filters – in order to meet the latest stringent emissions limits. According to Volkswagen, the particulate emissions of some of its petrol models can be reduced by up to 95% by fitting a filter to the exhaust system.
Why are petrol particulate filters being introduced?
Petrol-engined cars have been subject to particulate emissions limits since the EU5 standard was introduced in 2009. The permissible limits were reduced ten-fold in September 2018 when EU6c legislation came into force. This brought the NOx limit down to 60mg/km for new petrol cars, below the 80mg/km limit for diesels. This means particulates are virtually eliminated from exhaust emissions, including nanoparticles, which are considered to be more harmful than larger particulates.
How does a petrol particulate filter work?
There is a range of different systems, but those on petrol-engined Volkswagen Group cars work like a three-way catalytic converter, through which exhaust gases flow after exiting the engine and going towards the exhaust pipe. The unit is situated just behind the engine, close to the turbocharger. This helps it warm up quickly – useful because it needs to be hot to work effectively.
Exhaust gases are forced through the filter, wherein the trapped unwanted hydrocarbons (HC), nitrous oxides (NOx) and carbon monoxide (CO) particulates are heated up and reduced to small amounts of carbon dioxide (CO2), nitrogen and water.
After leaving the filter, the gases pass through a second, conventional three-way catalytic converter mounted beneath the floor. This ensures the tailpipe exhaust complies with the latest level of EU6c emissions standards even when the engine is working flat out.
Which cars are fitted with petrol particulate filters?
Early adopters of petrol particulate filters include Ford, Mercedes, Porsche and the Volkswagen Group. However, the technology has been introduced to most new petrol models introduced since September 2018 in order to meet the EU6c requirements.
Do petrol particulate filters need maintenance?
According to manufacturers, cars with petrol particulate filters shouldn’t need to regularly be driven at higher speeds for short periods like diesels to stop them from getting clogged up with soot.
This is because petrol particulate filters aren’t prone to getting blocked up like diesel particulate filters because petrol engines heat up quicker and run hotter than diesel engines, so more of the soot that’s collected in the filter is burnt off. Additionally, Porsche says that the electronic control units in its cars will detect when soot particles occasionally need to be burned off and automatically increase the exhaust gas temperature to do this.
Should I buy a car with a petrol particulate filter?
Petrol cars fitted with particulate filters are among the cleanest cars on sale, and there's no evidence so far that the filters will suffer the problems that have proved costly for some diesel car owners.
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