Semi truck mechanic here
A DPF is a Diesel Particulate Filter. It’s sole job is to catch the soot/carbon suspended in the exhaust fumes as it’s flowing through your exhaust. Basically, a DPF is a soot filter
Like all filters, they get blocked up/full up after a while, and it can no longer filter properly. So when a DPF is full, it’s basically sooted up/clogged up with loads of carbon.
A DPF Regeneration is the process a vehicle does to clean out the filter. Basically, the soot clogging up the DPF can be burnt out. That’s why it increased your revs, because it’s trying to get the exhaust temperature inside the DPF as hot as safely possible to burn out all the soot, which empties the DPF out.
In Semi trucks, I can’t speak for all of them because I only know Volvos, but they actually have a diesel injector inside the exhaust pipe just after the turbo, and just before the DPF. It’s sole purpose is to spray fuel into the exhaust during a DPF regeneration which then ignites and gets the exhaust VERY hot.
When I get a truck on a regen, the exhaust temperature is around 600°C (1,110° F). So yeah, basically, a DPF regeneration is the vehicle getting the DPF hot and burning out all the soot that’s blocking it up.
To my knowledge I don’t think any cars have a fuel injector in the exhaust for DPF regens though, A) because the DPF on a car is much smaller so it wouldn’t need a heat so extreme, but also cars are much more compact and if the exhaust was at 600°C in a car it would probably melt or set fire to everything surrounding it lol.
Also, to anyone wondering why I said semi truck, and then used Celsius instead of farenheit, I’m actually from the U.K. . We call them lorries or trucks here, but people who aren’t from the U.K. don’t seem to understand what I mean when I say lorry, and if I say truck then it’s vague as to whether I mean a heavy goods vehicle, or a pickup truck, especially since truck in america could mean pickup truck or semi truck lol.
The note changes because it is delaying the burn of the diesel, so it leaves the cylinder head still burning.
Normally it would be injecting earlier, so it can do as much burning and expansion in the cylinder, but the regens will delay that or add a little diesel after the main squirt.
The diesel burning through the exhaust increases the exhaust gas temperatures, and will get the DPF to 800degC / 1500F which should be hot enough to burn the soot.
That’s also why the sound of the exhaust changes too.
When it does happen, carry on driving as normal, or if you get the chance, cruise at a steady speed and it’ll stop after maybe 5-10 mins and the DPF soot filter in the exhaust should be cleaner.
There’s a thing in a diesel exhaust system called a Diesel Particulate Filter (DPF). When the truck is working at low RPM a lot (like when you’re stuck in traffic), the filter accumulates some soot from the burning fuel. If you drive at high RPM, the soot will burn off and you don’t have to worry about it. But if you’re stuck in traffic or something, the engine needs to take measures to burn that soot off by running at higher RPMs for a while.
Some trucks will have a way for the driver to start it manually, but it will usually happen automatically. Letting that filter breathe freely keeps the engine running smoothly and efficiently.
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