For those that don’t know, a GPF (gasoline particulate filter) is a type of substrate that goes in an exhaust system to filter out soot particles. It does that by forcing the exhaust through the porous wall of a substrate. By forcing the exhaust through the wall of the substrate, it filters out most of the soot the engine creates during combustion. Substrate manufactures can play around with the porosity of the particulate filters to optimize filtering ability and back pressure. These substrates are also typically coated with a washcoat similar to or the same as a TWC (Three-way catalyst) found on every gasoline vehicle now.
Since a GPF is a filter, it does need to be periodically cleaned through a process known as regeneration. The regeneration process works by oxidizing the soot particles that the GPF captures into CO2. The regeneration process will be slightly different on a gasoline engine compared to a diesel engine with a DPF. Gasoline engines produce significantly less soot than a diesel, so the soot loading will be significantly less and need to regenerate and clean out the particulates will also be reduced or depending on driving habits could be completely unnecessary. The soot oxidation process occurs at exhaust temperatures above 600C, which is very common on gasoline engines depending on placement of the catalysts and driving conditions. Since gasoline engines have higher exhaust temperatures but little to no available oxygen in the exhaust stream, most of the soot oxidation will occur passively during fuel cutoff deceleration. Since no combustion will be occurring, oxygen becomes available in the exhaust stream and when the temperature is above 600C, oxidation of the soot occurs. Although I’m sure the engine calibrations will have a defined active GPF regeneration strategy like on diesel engines, I imagine it only being used if someone granny cycles the car in extremely cold weather. The OEMs will also need to limit the use of active regeneration on gasoline engines because, in theory, that would increase the amount of NOx emissions. The reduction of NOx emissions by a TWC requires a rich A/F ratio so when the engine is running lean to oxidize the soot in the GPF, there will be an increase in NOx emissions.
On a diesel, they have to manually raise the exhaust temperature to the 600C target by injecting extra fuel into the exhaust so it is available to be oxidized, i.e. create heat, by the diesel oxidation catalyst that is placed in front of the DPF. Then since diesel’s run lean, the increased heat will burn the soot out over the course of the regeneration.
The addition of GPF will also have an impact on motor oils. Manufactures will start to require low-SAPs oil to protect the GPF from getting clogged early. The reason for that is, sulfated ash, phosphorus, and sulfur get captured by the filter and are unable to be burned out. Unlike soot which can be burned out, SAPS just get stuck in the particulate filter. Although, as long as the OEMs control oil consumption and size the GPF appropriately, a clogged GPF from low-SAPS oils shouldn’t be a problem.
Pros and Cons of particulate filters.
The major pro of them are less ultra fine (PM2.5) will be getting released into the air. PM2.5 is able to penetrate deep in lungs and cause damage to lung and cardiovascular system. PM2.5 is also known to increase the number of people with asthma and asthma attacks. It is also known to be a contributing factor in lung cancer too. So overall, a reduction in PM2.5 emissions is a good thing for overall health. Some testing the NIH (National Institutes of Health) did on a 2011 Ford F-150 with the 3.5 ecoboost showed between 85%-99% reduction in particulate matter emissions depending on the certification drive cycle. (FTP75, HWFET, US06)
The major con of having a GPF is the increased complexity, so there is a possible reduction in reliability.
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