how does a Diesel Particle Filter work in a car engine? Isn’t it pointless if it dumps the “particles” anyway?
In: Engineering
They do not just dump the particles. Some filters are single-use and need to be replaced when full. Others are designed to burn off the particle either passively through the use of a catalyst. Some have a cleaning cycle that runs the engine in a way that increases exhaust temperature, sometimes with fuel injected into the exhaust. At a higher temperature, the particle will combust.
What the filter captures is stuff that is not completely combusted, it will be completely combusted when it leaves the filter. That is for non-single-use variants.
It is a bit like asking why a catalytic converter in a car works. It just releases everything out the other end. The key to the function is not in the same form when it enters and exits the catalytic converter. Stuff that is not completely combusted gets completely combusted in the converter.
They’re meant to capture soot from the diesel exhaust, and then when you change the filter you’re meant to dispose of it properly.
Sure, if you just chuck the filter in your from lawn then all the soot is still getting out, but if you take it to an automated store to trash like you do with used oil then it’s better
A DPF captures particulates and soot. When the system determines it’s full, the computer will trigger a regeneration. The regeneration increases the temperatures, and burns the soot and hydrocarbons into ash. Eventually the filter will get too full of ash, and then it will need to be removed and cleaned or replaced.
The filter does not “dump” the particles.
When diesel fuel burns in an engine, it doesn’t burn completely, leaving microscopic particles of soot. These particles are hazardous to health when inhaled and are an important cause of lung health problems like asthma, and can also trigger heart attacks. They are also suspected to be a cause long term lung damage and cardiovascular system damage.
The purpose of the filter is to collect the soot particles, but it can’t just dump them out. Thankfully, soot is carbon, which is flammable. If the exhaust gases get hot enough, and there is enough oxygen in the exhaust, then the soot will actually ignite and burn out of the filter.
Filters are usually made with expensive metals like platinum or palladium. When soot touches these metals it becomes easier to ignite. This means that during hard acceleration or hill climbing, that the exhuast will be hot enough to ignite the soot, and the filter becomes self cleaning.
Sometimes, if you only do town driving, the exhaust never gets hot enough to burn off the soot. In this case, the car’s electronics will detune the engine – this will cause the engine to work very hard but run very inefficiently, and produce extremely hot exhuast gas, which will be hot enough to ignite the soot in the filter. This will happen automatically, and usually the car will tell you that it is happening, and warn you not to switch the car off, because otherwise the filter cleaning won’t finish.
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