Particulate filter for gasoline engines

Particulate filter for gasoline engines
Particulate filter for gasoline engines

Due to the higher exhaust temperature and different combustion principle, the soot particle filter in gasoline engines is continuously cleaned under normal conditions. Unlike diesel, regeneration does not require an increase in the fuel dose, so there is no danger of diluting the oil with gasoline.

Euro 6c and 6d exhaust emission standards, which include a new validation of measured values ​​in actual operation. Necessary technical changes, imposed by stricter rules, include the use of particulate filters for gasoline direct injection engines. In practice, this means for almost all petrol units, except for the simplest engines in small cars and atmospheric engines in hybrid plants.

While this seems to be related to the new measurement methodology, it is not. Her arrival has been known for quite some time in advance and is tied to the alignment of conditions for diesel and gasoline engines.

2.0 TFSI with particulate soot trap

Same principle, different practice - Particulate filter for petrol engines

Because particulate filters have the same purpose for gasoline and diesel engines, their basic principle of operation is the same. It consists of placing a ceramic liner in the exhaust pipe, which, in a very fine structure, collecting fine, individually invisible particulates from the exhaust gases by combining through the blind and passageways.

The so-called differential pressure sensor compares the exhaust flow upstream and downstream of the filter to determine the level of charge of the filter. When the filter is charged above normal operating level, the engine control electronics must initiate a forced ignition or regeneration of the filter to ensure the functionality of the car.

A simple soot particle filter has several different abbreviations in the world of gasoline cars, but they all mean the same thing. GPF, which in English means "Gasoline Particulate Filter". Unlike diesel engines, the German abbreviation is different, namely OPF ("Ottopartikelfilter"). This, for example, appears in the texts of Škoda, which, given the sharing of technology with the German Vw, cannot surprise. French terminology, on the other hand, makes no distinction between petrol and diesel filters; An alternative designation for the combination of filter and catalyst in one body (cGPF) is a four-way catalyst, which underscores the fact that a new function has been added to the existing three-way catalyst.

Filter regeneration scares modern diesel cars. To burn DPF (Diesel Soot Filter), it is necessary to increase the exhaust gas temperature by increasing the amount of fuel injection - whether it is injected directly into the cylinders or through a special injector into the exhaust gas. The car is therefore harder to drive and spend more. In addition, the eventual interruption of regeneration leads to further filling of the filter.

Particulate filter for gasoline engines
Particulate filter for gasoline engines

This is not the case with a gasoline filter called GPF. Engineers from car manufacturers swear that with normal use of gasoline cars with GPF, there will be no forced regeneration at all. This statement is supported by two physical arguments. On the one hand, petrol engines have a higher exhaust temperature, so the GPF will also heat up to a higher temperature during operation and have a better chance of burning continuously while driving. On the other hand, starting the filter will help the engine braking mode - that is, driving without throttle with the gear engaged. In this situation, the engine only pumps the intake air without injecting fuel. The natural concentration of oxygen is sufficient for the heated particles to burn in the heated filter.

However, forced GPF regeneration can still be applied - usually on short cold motor trips. For many other reasons, a gasoline engine with direct injection is not an ideal solution for such applications, but the situation on the market today is that most new cars have a more suitable drive, ie. Without a direct injection engine or in a hybrid or pure electric version, they simply do not buy.

Regeneration is the exact opposite of DPF

As with turbodiesel, the clogged filter should be combusted by artificially raising the exhaust temperature and igniting the particulates. The gasoline engine does not need to increase the fuel dose which can then be diluted with oil or if the regeneration fails further clog the filter.

The solution is just the opposite: poor mix. Gasoline in a gasoline engine is not only used for combustion, but also for cooling the combustion chamber or exhaust pipes. For example, owners of older Fabia with 1.2 HTP engines and eight-valve 1.2 TSI know about it in practice. The control units of these engines cool their relatively small catalytic converters under load by increasing their fuel fill, and therefore these engines have incredibly high fuel consumption when driving very fast. GPF regeneration results in the opposite application of the same principle in which the filter intentionally allows the filter to be heated to a higher temperature by reducing the fuel dose.

You don't know you have it in your car

There are two GPF setup sites. Generally less suitable, but sometimes more structurally desirable is its installation at the beginning of the horizontal section of the exhaust pipe under the car. For example, they have new generations Ford Focus and Kia Ceed. This layout can only be recognized by a thorough inspection of the underside of the car or from a parts catalog.

However, it is more widespread and practical to place the filter as close as possible to the engine, ie. vertically behind the exhaust manifold and turbocharger (if the car has one, which is in most cases). In this case, the filter is placed in a joint package with the catalyst and replaces the existing oxidation catalyst. Such an arrangement is sometimes called cGPF (closed soot filter) and provides quick and easy heating of the filter to operating temperature. A layman has no chance of recognizing it - unless he examines the sensor wiring in detail or notices the pipes leading to the differential pressure sensor.

Designers used cGPF designers for example upgraded the Skoda Fabia with a 1.0 TSI engine, the same way it switched to Fiat to the new 1,0- and 1,3-liter turbocharged engines from the Firefly or Renault series to the new generation of their petrol engines. The small advantage is that this architecture forces engineers to deal effectively with other parts - using compact water-cooled exhaust manifolds and placing the turbocharger as close to the engine as possible. This brings additional advantages in practical work.

The compact design is also typical of cGPF, which is also the answer to the question that many people who are interested in a new gasoline car worry about. The diesel particulate filter will almost always burn naturally near the engine, its lifetime should be equal to the usual three-way catalytic converter, and if a cGPF replacement occurs, the cost and effort of replacement will be comparable to existing catalysts. To date, cGPF can only be destroyed if the driver ignores excessive oil consumption.

We can't do without him

In fact, the presence of a soot filter in a car with gasoline is the only practical drawback. According to the first experience, cars equipped with GPF do not "drive" as we are used to - especially transient modes, when the driver needs a sharp acceleration after a smooth ride.

Since GPF reduces exhaust pipes, part of the blame is undoubtedly on it. However, it should be borne in mind that the Euro 6c and 6d standards now require that the actual car (RDE test) not exceed the measured emissions of nitrogen oxides and particulates more than 2,1 times. Under these conditions, it is not possible to inject as much fuel as it can burn into the engine to achieve the required power, but everything must be carefully monitored and dosed.

Leave a reply