Diesels have long used pollution-negating filters, but now petrols are getting them too
7 May 2018

Volkswagen is introducing gasoline particulate filters (GPFs) to its petrol cars as part of wider plans to improve emissions across its whole range - and it predicts reductions of particulate emissions in some models by up to 95%.

The Up GTI gained GPF technology earlier this year, but the device was already used on the manual-transmission variant of the Tiguan 1.4 TSI in Germany and is being rolled out across the brand's other cars.

The measures follow a commitment made by VW in 2016 to fit particulate filters to petrol engines, as the company sought to bounce back from 2015’s Dieselgate scandal.

Other manufacturers are equipping their own petrol cars with GPF systems. Mercedes-Benz, for example, fits it to some S-Class derivatives and, like VW, plans to roll it out more widely across its fleet. Ford has the system on its new Mustang, among other models.

Petrol cars have been subject to particulate emissions legislation since the introduction of the EU5 standard in 2009. The latest stage, EU6c, was introduced in September 2017, forcing petrol engine particulate emissions to be reduced by 10 times the previous level.

The VW particulate filter doubles as a three-way catalytic converter, the device normally fitted to petrol car exhausts to reduce emissions of toxic gases. Conventional three-way catalytic converters contain a ceramic honeycomb called a substrate, through which the exhaust gases flow on their way to the tailpipe. The substrate has a catalyst coating that greatly cuts levels of the three main toxic gases in exhaust: unburned hydrocarbons (HC), oxides of nitrogen (NOx) and carbon monoxide (CO).

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Traditionally, the focus has been on larger diesel particulate matter up to 10 microns in diameter (PM10), or smaller PM2.5. By comparison, a human hair is around 70 microns in diameter. But as far back as 2001, a new threat came to light in the form of nanoparticles, which are more than 100 times smaller than a PM10.

A report commissioned by the Swedish National Road Administration revealed that under certain conditions, some petrol vehicles were emitting the same number of nanoparticles as diesels.

The quantity of particulates in exhaust had previously been measured by weight, but awareness of nanoparticles grew after the use of alternative measurement techniques. Although nanoparticles weighed very little, they were present in large numbers and capable of covering a large surface area. The concern was that nanoparticles could penetrate deeper into the lungs than larger particles. Like diesel particulate filters, the GPF is designed to capture all sizes of particles, including nanoparticles.

However, different types of particulate matter are produced by a variety of sources, including brakes, tyres and road dust. According to a study by DEFRA, such sources can produce equal amounts of particulates to that of road vehicle exhaust gas.

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How the petrol particulate filter works: 

The new filter is tucked in behind the engine a few centimetres from the turbo, heats up very quickly and becomes effective seconds after starting from cold. At its core, exhaust is forced through the walls of channels blocked off at alternate ends. The trapped particulates are superheated, reduced to CO2 and, at the same time, the unwanted HC, NOx and CO are converted to small amounts of CO2, nitrogen and water.

After leaving the filter, exhaust 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. The Up GTI is subject to the new WLTP (World Harmonised Test Procedure) and RDE (Real Driving Emissions) testing standards. Like EU6c, WLTP applies to all new types of car introduced after September 2017. WLTP should ensure the quoted emissions are much closer to real world outputs.

Read more 

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Comments
8

7 May 2018

Port injected gasoline cars don't have this problem to anything like the same extent...

7 May 2018

When DPFs first came out manufacturers were advertising that their cars had them fitted, even in the model names. The GPF roll out seems altogether quieter and perhaps that's not surprising given the problems that DPFs can cause. So this begs the question what are the long term maintenance requirements of a GPF? Petrol doesn't produce as much particulate matter as diesel so does that mean it's not something to worry about, much like a catalytic converter or is this just another expensive component to go wrong or at the very least requires a change in driving style or additional maintenance?

7 May 2018
Does this mean we can expect petrol engined cars to suffer from the same issues as diesels for low mileage drivers? Blocked particulate filters etc?

7 May 2018

 No, not really it may do what it says on the Tin but it’s just another cost to th e motorists, something else to go wrong more weight and so on.....

Peter Cavellini.

7 May 2018
The problem with emission reducing devices (CAT, DPF, SCR) is that when they are introduced, they are initially fitted to cars that were designed without considerayion for such devices and therefore without the space to fit them in the most efficient way. For instance, CATs were initially fitted under the car. This caused them to reach working temperature more slowly, and when they did, they were at risk of igniting dry leaves. DPFs were initially too far from the exhaust manifold, which prevented proper regenrration.

7 May 2018

Please use correct language - i assume they are reducing particulates to a tenth of the previous level, you cannot reduce by ten times!

7 May 2018

Another VW sponsored puff piece - you cannot polish a turd.

8 May 2018

That's good news. Volkswagon always make an edge over the automobile industry.

by..........interior designer in Ernkulam

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